Shorter Contributions 

to General Geology 

1958

GEOLOGICAL SURVEY PROFESSIONAL PAPER 334

This Professional Paper was published 

as separate chapters A H

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington 25, D.C.
CONTENTS

[The letters in parentheses are those used to designate the separate chapters]

Page

(A) Tables for the calculation of lead isotope ages, by L. R. Stieff, T. W. Stern, Seiki Oshiro, and F. E. Senftle_________ 1

(B) Fossils of the Littleton formation (Lower Devonian) of New Hampshire, by A. J. Boucot and Robert Arndt_________. 41

(C) Trilobites of the Upper Cambrian Dunderberg shale, Eureka district, Nevada, by Allison R. Palmer_ _-____-___-__-__ 53

(D) Late Paleozoic Gastropoda from northern Alaska, by Ellis Y. Yochelson and J. Thomas Dutro, Jr___________________ 111

(E) Upper Cretaceous Pelecypods of the genus Inoceramus from northern Alaska, by David L. Jones and George Gryc_____ 149

(F) Ammonites of Early Cretaceous age (Valanginian and Hauterivian) from the Pacific Coast States, by Ralph W. Imlay_ 167 

(G) Dispersion characteristics of montmorillonite,kaolinite, and illite clays in waters of varying quality, and their control

with phosphate dispersants, by B. N. Rolfe, R. F. Miller, and I. S. McQueen___________________________________ 229

(H) Geology of southeastern Ventura basin, Los Angeles County, California, by E. L. Winterer and D. L. Durham________ 275

ni

U.S. GOVERNMENT PRINTING OFFICE : 1962 O -581734
Tables for the Calculation 

of Lead Isotope Ages

By L. R. STIEFF, T. W. STERN, SEIKI OSHIRO, and F. E. SENFTLE 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOG

GEOLOGICAL SURVEY PROFESSIONAL PAPER 334-A 

Tables for the calculation of geologic age using the

. .' r r>l206/TT238 DU207/TT23S D U 207 I r> U 206 atomic ratios oj rb /U , rb /U , rb /rb , 

and Pb208 /Th 32. This report concerns work done on 

behalf of the U. S. Atomic Energy Commission and 

is published with the permission of the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

The U. S. Geological Survey Library has cataloged this publication as follows:

Stieff, Lorin Roll ins, 1920-

Tables for the calculation of lead isotope ages, by L. K. 

Stieff f and others] Washington, U. S. Govt. Print. Off., 

1959.

iv, 40 p. diagrs., tables. 30 cm. (U. S. Geological Survey. Professional paper 334-A. Shorter contributions to general geology)

"Tables for the calculation of geologic age using the atomic ratios 

of Pb206/U238, Pb207/U235, Pb207/Pb206, and Pb208/Th232." 

Bibliography: p. 7.

1. Lead Isotopes. 2. Isotopes Tables, etc. 3. Geological time 

i. Title. (Series: U. S. Geological Survey. Professional paper 

334-A. Series: U. S. Geological Survey. Shorter contributions to 

general geology)

550.1

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 35 cents (paper copy)
CONTENTS

Abstract-- _ __________________________

Introduction ___________-_-_---_____-_

Methods of computation--_____-_______

The Nd/Np relation.______________

The Nw/Nm relation___.,._____.__

Sample age calculation________________

Correction for original common lead.

Page 

1 

1 

3

3

4

5

6

Sample age calculation Continued

Pb2oe/U2»8 age method___.__________._.

Pb207/U23B age method__________.__.__.

Pb207/Pb206 age method..._______________

Pbzos/Th232 age method_______-_____._.

Literature cited.________..-______--__-__-_

Tables for the calculation of lead isotope ages.

ILLUSTRATIONS

Page

6

7

7

7

7

9

FIGURE 1. Atomic ratio Nd/Np plotted against the age, t, showing the plus and minus tolerance curves.-. 

2. Atomic ratio Nw,/Nm plotted against the age, t, showing the plus and minus tolerance curves.

TABLES

TABLE 1. Physical constants used in calculation of tables-__.______-_-___---__-_---__-__-

2. Errors in t produced by uncertainties in the physical constants used in calculation.

3. Range and interval of <_________.__.________-_______..______________________.

4. Decay constants X,- (y-1 ).-_-_____._.___-_____-_-______-__-________-_-______-

m
	LETTER SYMBOLS

X decay constant

t age, in millions of years

T half life

N number of atoms

Nd number of atoms of daughter products

Np number of atoms of parent

k present-day atomic ratio of U238 to U235

V year

R atomic ratio
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

By L. R. STIEFF, T. W. STERN, SEIKI OSHIRO, and F. E. SENFTLE

ABSTRACT

Tables are presented for calculating geologic age by using the

atomic ratios of Pb2°«/U238 , Pb2°YU235, Pb207/Pb206, and Pb2"8/Th232 .

Tables of values of Nd/Np and t are given for the age equation

where A is the decay constant,

t is age, in millions of years,

Nd is the number of atoms of daughter products, 

and Np is the number of atoms of parent.

Values for Ntm/Nm and t are also given in tabular form for 

the age equation

A/2 1)

where N^m and A/2oe are the number of atoms of radiogenic Pb207 

and Pb206, respectively, and where k, the present-day atomic 

ratio of U238 to U235, is taken as 137.7. The half lives (T) of 

U238, U235, and Th232 used in the calculations are: r238 =4.51X 109 

years, 71235=7.13X108 years, Tm=lA2X 1010 years.

The tables cover selected values of t from 1 to 6,000 million 

years (6X 109 years) at intervals of t ranging from 1 to 15 million 

years. Only the calculated errors in t resulting from experimental uncertainties in the determinations of the decay constants and relative abundance of U238 and U235 have been included. An example is given for a hypothetical geologic age 

calculation by use of these tables.

INTRODUCTION

Although lead isotope age calculations are in general 

not difficult to make, both graphs and nomographs are 

available in the literature to simplify these computations. Holmes (1931, p. 208) published in "The Age of 

the Earth" a graphical solution of the age equation 

involving total lead, uranium, and thorium. Eight 

years later Wickman (1939, p. 6) published several 

nomographs that gave ages in millions of years equivalent to the weight ratios of Pb206/U238, Pb^/Pb206, and 

Pb208/Th232. More recently, Kulp and others (1954, p. 

345) have prepared nomographs of the three age ratios 

mentioned above as well as the ratios of Pb207/U235 in 

terms of numbers of atoms rather than in weight 

percent.

During the course of geochronological studies mr-de 

by the U. S. Geological Survey it was found desirable 

to have age equivalents for the various lead isotope 

ratios at smaller intervals and over a greater range of 

time than could be obtained from the references mentioned above. Initially, these tables were calculated 

for the atomic ratios of Pb206/U238, Pb207/U235, Pb^/Pb206 , 

and Pb208/Th232 at intervals of t of 1 million years from 

1 million years to 6,000 million years. The tables in 

this paper are an abridgment of the original tables. 

The calculations were carried to 6,000 million years, an 

age greater than the probable age of the earth, so tH.t 

speculative calculations could be made. They are 

being published because it has been found that for 

certain types of analysis of isotopic age data these 

tables are more satisfactory than the published nomographs. For example, the tables offer greater accuracy 

and ease of manipulation than the nomographs in 

making repeated solutions of the age equations. Siich 

repeated calculations are particularly useful in evaluating different geologic processes which have produced 

discordant ages.

The general form of the age equations used to compute the tables was developed by Kovarik (1931, p. 73), 

Keevil (1939, p. 195), and others. Solutions were 

obtained for equations of the form

The equation

N_d 

N,

'207

=expX£ 

& (expX238< 

was solved by iteration. It is important to note that 

the ratios otNJN, and Nm/Nm in the present tables 

are given as ratios of number of atoms of daughter 

(Nd) to number of atoms of parent (Nf), and number 

of atoms of Pb207 (Nwi) to Pb206 (Moe) and not in terms 

of weight percent.

The authors wish to express their appreciation to 

F. W. Reilly and D. B. Rock of the Computer Branch 

for their aid in the operation of the computer, and also

1
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

to Raynor L. Duncomb, Julena S. Duncomb and 

G. M. Clemence, of the U. S. Naval Observatory, for 

their cooperation and help in preparing the tables for 

printing. This work is part of a program being conducted by the U. S. Geological Survey on behalf of the 

Division of Research of the U. S. Atomic Energy 

Commission.

The half lives, decay constants, and ratio of U238/U235 

used in the calculations are shown in table 1, along with 

those used by Wickman and by-Kulp and others. The 

values used in this paper were chosen for the following 

reasons. Fleming and others (1952, p. 642) discuss in 

some detail the earlier work on the determination of 

the half life of U235 . The weighted average of all

previous measurements is numerically tl ?- same as their 

value with a slightly larger probable error. The halflife data of Fleming and others was therefore chosen 

for these calculations. These authors have also discussed the past determinations of the I alf life of U238. 

From their "best values" a half life of (4.51 ± 0.007) X 

109 years has been calculated. More recently Kovarik 

and Adams (1955, p. 46) have redetermined three of 

their original specimens. Their newest value, (4.507± 

0.009) X109 years, lies within the limits of error of the 

"best value" calculation of Fleming and others. In 

view of the small differences in half lives, as well as the 

differences in probable error, a value of (4.51 ± 0.01) X 

109 years was therefore chosen.

TABLE 1. Physical constants used in calculation of tables

Nuclide

U238 .

U235 _ __ _ - .

Xh232

Atomic ratio IT238/!!235 _____________ _

This paper

i T= (4.51 ± 0.01) X109 y

X=1.5369 X10-1°y-1 

i T=(7.13±0.16)X108 y

X = 9.72|,X10-1V1 

2 T=(1.42±0.07)Xl010y

X=4.88, 3 X10-»y-1 

3 137.7±0.32

Kulp and others, 1954

T= (4.49 ± 0.0 l)X109y

X=1.541X10-10y-1 

T=(7.13±0.16)X108y

X = 9.722XlO-10y- 1 

T=(1.39±0.02)X1010y

X= 4.987 XW-ny~l 

137.7 ±0.5

Vickman, 1939

!T=4.56X109y

X=1.52X10-i°y-1 

T=7.14X108y

X=9.72X10-10zr1 

T=1.39X10«>y

X=4.99X10-"y-1 

139.0±1.0

1 Fleming and others, 1952, p. 642.

2 Senftle, Parley, and Lazar, 1956, p. 1629.

3 Senftle, Stleff, Cuttitta, and Kuroda, 1957, p. 189.

Kovarik and Adams (1938, p. 413) have also determined the half life of Th232 as (1.39±.03)X1010 years. 

In their very thorough and excellent paper they determined in addition the branching ratio of Bi212 . Recently 

this branching ratio and the half life of thorium have 

been redetermined by Senftle, Farley, and Lazar (1956). 

Using a pulse-counting technique they obtained a 

branching ratio 7.4 percent higher than that obtained 

by Kovarik and Adams. Although the half life as 

determined by Kovarik and Adams does not directly 

depend on the branching ratio of Bi212 , the half life 

was determined from the basic alpha-count data. In 

spite of the careful alpha-counting techniques used by 

Kovarik and Adams, the differences in the branching 

ratio of Bi212 raise some questions on the earlier Th232 

half-life determinations. Also, their calculations depended on the existence of radioactive equilibrium 

between Th232 and Th228 based on the age of the thorite 

and the assumption that the daughter products were 

undisturbed by processes of alteration and weathering. 

Senftle, Farley, and Lazar, however, have shown that 

even for a specimen of fresh thorite chosen because it 

showed no signs of alteration, the Ra224 was 9.5 percent 

less than the equilibrium amounts; this implies a loss 

of its parents Th228 and Ra228 . The tendency of radiogenic daughter products to migrate has been pointed

out in detail by Rosholt (1958). Hence, the value of 

the half life (1.42±0.07)X1010 years as determined by 

Senftle and others was used, even though the quoted 

percent of error is somewhat larger than that of Kovarik 

and Adams.

The determination of the atomic ratio N238/N235 has 

been discussed by Fleming and others (1952, p. 642). 

They observe that a mean value of 137.7 "falls within 

the limits of error of all values reported." Kulp and 

others (1954, p. 345) used a value of 137.7±0.5. 

More recently Senftle, Stieff, Cuttitta, and Kuroda 

(1957, p. 190) have shown an average value of 137.7 ± 

0.32 for 13 uranium specimens. Thi? value with its 

somewhat smaller probable error has been used for 

these calculations.

In general, the ratios in the tables r,re given to four 

significant places, a value somewhat better than can 

be justified by present physical measurements and 

analytical methods. The remaining two numbers in 

smaller type have been included because of their 

usefulness in certain theoretical calculations. Corresponding to each ratio a value of t plus or minus the 

error may be read from the tables or may be directly 

interpolated as a first approximation if the exact value 

of the ratio desired is not found. Tl e limits of error 

for t shown in the tables have been calculated by 

using only the limits of experimental error reported for
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

the determinations of the decay constants and the are treated more fully in the section "Methods of 

abundance ratios, and the error term has been rounded computation." 

to the nearest 0.1 million years. The error calculations

TABLE 2. Errors in t produced by uncertainties in the physical constants used in calculation

Age method

pb206/U238

pb207/U235 ____________________________________

Pb207/Pb206 ___ ___-_-_-_--____-_-_. _ _ _

Pb208/Th232__ ____________________________________

Errors In calculation of various ages, both in millions of years

100

±0. 22

±2. 24 

±57. 18 

±4. 93

500

±1. 11

±11. 22 

±63.95 

±24. 65

1,600

±3. 33 

±33. 66 

± 82. 21 

±73. 94

2,500

±5.54 

±56. 10 

± 102. 38 

± 123. 24

4,500

±9. 98 

± 100. 98 

± 146. 50 

± 221. 83

6,000

± 13. 30 

± 134. 69 

± 181. 65 

± 295. 77

Table 2 lists for several different t's the limits of error 

in the age calculations resulting from the uncertainties 

in the physical constants used. This table shows that 

the limits of error in calculated age for the Pb206/!!238 

method are less than the limits of error for the other 

three methods. The selection of intervals of t (table 

3) was determined in part by the limits of error for the

TABLE 3. Range and interval of t

Range (years)

!X10«to 500 X106 

500X106 to 1,500X10* 

1,500X10* to 2,500X10* 

2,500X10* to 4,500X10* 

4,509X10* to 6,000X10*

Interval (years)

1X10* 

2X10« 

5X10* 

10X10* 

15X10*

might be obtained for the same value of t. Admittedly, 

the intervals chosen for the abridged tables are smaller 

that the uncertainties in the calculated ages introduced 

by the most precise analytical techniques currently 

available. However, improvements in the quantitative 

determination of lead, uranium, thorium, and hotopic 

abundance may ultimately permit the measurersent of 

small differences in age (1 to 2 million years) of radioactive minerals from rocks of Cambrian age or younger.

METHODS OF COMPUTATION 

THE Nd/Np RELATION

For the purpose of programing this work for the 

digital computer, the general form of the age ec uation 

was used,

"Tr" ** & _ T> ___\ j 1

J.\1i

(1)

method. In spite of the larger errors inherent 

in the other methods, the same interval of t has been 

used for all four tables in order that equivalent ratios

where i=l, 2, 3 

and .7=1, 2, 3.

The values of the decay constants with their limits, 

X, , used for these calculations are shown in tab11 ^ 4.

TABLE 4. Decay constants \i.(y~')

X

U238Ai 1 = i.5369 xiO-10 

U28«X2 , = 9.7216 X10-10 

Th232X3. = 4.8813X10-"

X plus error

Xi2 =1.5335 X10-10 

H = 9.5082 X10-10 

*32= 4.6520 X 10-"

X minus error

*i3 =1.54o3 X10-»° 

X23 = 9.9447X10-'°

*33 =5. 1344X10-" ^

In computing expX^f 1 the exponential series was 

expanded

to the uncertainties in the decay constants was simplified in the following graphical treatment shown in 

figure 1. By virtue of the geometry in figure 1,

and the recursion -. --. -= . was used to evaluate (n l)\n n\

the series. No round off was used in the evaluation 

and the maximum error in expX^Z can be shown to 

be less than 5X10"5 .

The problem of calculating the errors in the ages due

where t2 is the age for a plus error in X 

and £3 is the age for a minus error in X. 

Therefore,

and

(3b)
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

t

FIOTJRE 1. Atomic ratio Nd/Np plotted against the age, t, showing the plus and minus tolerance curves.

Simplifying and taking logarithms,

and

(4a)

(4b)

Also it is evident from figure 1 that MN=ti t3 and 

NO=t2 ti. Thus, by the substitution the error in the 

age, MN and NO, can be simply evaluated in a convenient form,

and

N0=tl l?-

(5a)

(5b)

If new, more nearly accurate, values of the decay 

constants become available, it is a simple matter to 

obtain the corrected age from the tables. For example, 

suppose the half life of the Th232 is changed from 1.42± 

0.07X1010 years to 1.45±0.02X1010 years. Calculated in this way using T instead of X, the new value 

of the age, </ say, will be

. , 1.45 t.

1.42

Similarly, t2 ' and t3 ' will be

1.47

and

1.42

1.43 t '' 1.42

Then, if one assumes an experimental ratio of A^os/A^a 

of (O.OSOOaa), the corresponding value of ti (A^os/A^ 

table) is 1,OOOX106 years. The new half-life 

value would yield </, tj', and t$ ages of 1,021 X106 

years, 1,035X106 years, and 1,007X106 years, respectively. Thus, the tables can still be used even if new 

values of the half lives are redetermined at a later date.

RELATION

(6)

THE

The general equation,

Nm_v_ expV- 1

'206 *l( ji 1)

was used for computing the Pb207 /Pb206 table. The 

value, ki, used for the U238/!!238 atomic ratio was 137.7 

±0.32 where fc2 and fe3 designate the aburdance ratios 

with the plus and minus tolerances, respectively.
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

As in the Nd/Np relation previously described, the 

calculation of limits of error in the age due to uncertainties in the decay constants has been simplified for 

programing on the digital computer. By use of a 

similar graphical argument as shown in figure 2, it 

can be seen that

i 1 _ expX22 £2

and

R=

 1) k2 (expXl2 «2 1) 

 1 _ expX23 £ 3 1

:-!) k3 (expXl3 * 3 -l)

(7a)

(7b)

However, unlike the previous solution, the equations 

(7a, b) have no direct solution for t2 and t3 and an 

iterative-approximation method had to be used. The 

left-hand sides of the equations can be evaluated. 

The right-hand sides are quotients of infinite series in 

t2 and t3 . An initial guess was made for t2 or £3, as the 

case may be, and a test for equality was made. Successive approximations were made to the t values until 

equality was obtained.

For the particular case where tl = t2=t3 Q, the ratio 

R is indeterminate. However, by using L'Hospital's 

ule an approximate but quite accurate value of R can

be obtained. Hence, the limits of the ratios as- t\, t2) 

and <3 ->0, are #:=0.045936 , #2 =0.0449, ard R3 

=0.0470. Thus, radiogenic lead being formed at the 

present time should and does have a NWI/NSM ratio 

between 0.045 and 0.047, a value very close to the 

experimentally observed value.

From the age tables it can be seen that below an age 

of 56X106 years, the Pb^/Pb206 method has errors 

that are larger than the calculated value of t. As has 

been mentioned, this error is due only to the uncertainties in the physical constants used in the calculations. 

It is shown in figure 2 for an age t, (which is lesn than 

56X106 years) that the horizontal line (a-6) between 

the ages representing the plus and minus tolerances does 

not intersect the upper curve on the positive side of 

the coordinates because of the flatness of the curves 

in this region. Also, this "flatness" and the round-off 

error cause oscillation of approximately 0.1 to 1.0 

million years in the quoted error in t for ages lesr? than 

400 million years, and small irregularities in tl ^ 5th 

and 6th places of the A^/A^oe ratio for the range from 

0 to 50 million years.

SAMPLE AGE CALCULATION

A hypothetical uraninite gave the following chemical 

data: U=43.646 percent, Pb=7.532 percent, Th=5.20!

N207

N,206

/?, = 0.0470

/?, = 0.0459 

/?2 = 0.0449

485342 O 5£

FIGURE 2. Atomic ratio Nsm/Nim plotted against the age, t, showing the plus and minus tolerance curves.
6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

percent. For an exact age solution in terms of numbers 

of atoms it is not necessary to convert these data from 

the chemical to physical scale of atomic weights by 

multiplying these values by the conversion factor 

1.0002783 given by Nier (1950). This conversion factor 

cancels out in the lead-uranium ratio age calculations. 

However, for an exact age solution, it is necessary to 

use the calculated physical atomic weight of the lead 

based on the isotopic composition of the sample being 

dated rather than the physical atomic weight of average 

common lead, 207.282. The physical atomic weight of 

this hypothetical radiogenic lead is obtained by multiplying the four lead atom percent abundances by the 

respective physical atomic weights for the individual 

lead isotopes. Using the isotopic atomic masses given 

by Sullivan (1957), 204.0368, 206.039, 207.041, and 

208.041, the calculated atomic weight of the radiogenic 

lead in the uraninite is 206.32. The weight percent 

of lead corrected for this small factor is :

Failure to correct for differences in atomic weight will 

result in errors of approximately 0.2 to 0.5 percent in 

the calculated lead-uranium and lead-thorium ages 

depending on the atomic weight of the lead in the 

radioactive mineral and the physical constants used in 

the calculation.

Isotopic analyses, in atom percent, of lead in uraninite and associated hypothetical galena

Pb204

Pb208

pK207

pVj208

Lead In 

Uranlnlte

0. 1957 

81. 178 

8. 642 

9.984

Associated 

hypothetical 

galena

1.43, 

23. 30, 

23. 277 

51. 98!

The presence of lead originally deposited (common 

lead) with the uraninite and not produced by the radioactive decay of the uranium or thorium in the mineral 

is indicated by 0.1957 percent Pb204 in the isotopic 

analysis of the lead extracted from the uraninite. 

Pb204 is the only isotope of lead not known to be produced by radioactive decay. The isotopic analysis of 

the hypothetical galena associated with the uraninite 

is assumed to approximate closely the isotopic composition of the nonradiogenic lead originally deposited 

with the uraninite. As this galena also contains Pb206 ,

Pb207, and Pb208 , it is necessary to correct the uraninite 

lead before the age calculations can be made.

CORRECTION FOB ORIGINAL COMMON LEAD

The correction for the original common lead may be 

made in the following way:

1. Using Pb204 as the "index" of the amount of 

original lead present, a factor proportional to the 

amount of Pb204 present in the uraninite (0.1957) compared to the Pb204 in the galena (1.438 ) is obtained.

0.1957 

1.43B

=0.13628

2. This factor, when multiplied by the percent 

abundances of the lead isotopes in the associated 

galena, will give the proportional amounts of Pb204 , 

Pb206 , Pb207 , and Pb208 originally present in the uraninite.

Pb204 =1.436 X0.13628 =0.1957 

Pb206 =23.306 X0.13628 =3.176 

Pb207=23.277 X0.13628=3.172 

Pb208 =51.981 X0.13628=7.084

3. The isotopic analysis of the lead, in atom percent, 

from the uraninite is then corrected for the original lead 

present.

Isotopic analysis of uranIsotopic analysis of original lead present __ ___

Radiogenic lead produced by U+Th _ ...

Pbiw

0. 1957

-. 1957

0.000

Pb«»

81. 178

-3. 17,

7&002

Fb«"

F. 642

-?. 172

f . 470

Pb*»

9. 984

-7.084

2. 90o

AQB METHOD

The Pb206/U238 age is obtained by first multiplying 

the weight percent (chemical scale) of totrl lead by the 

corrected percent of radiogenic Pb206 produced by the 

uranium and dividing by the weight perc3nt (chemical 

scale) of total uranium multiplied by the atom percent 

abundance of U238, that is 7.567 X78.00; divided by 

43.646 X99.27s. It is then necessary to convert this 

weight ratio into an atomic ratio by dividing the 

physical atomic weight of the uranium, 2?8.103, by the 

physical atomic weight of the lead, 206.32; that is,

238.103

206.32 = 1.154oAs Avagadro's number would appear in both the 

denominator and numerator, it can be canceled out
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

without altering the numerical value of the ratio 

Nd/Np . The age calculation thus becomes

7.567X78.002 \,-i -leA _ rk I K7Q

=43646><99>273 X1.154o-0.15720.

From the tables read 950 ±2.1 million years. 

Pb2o7/xj2sj AGE METHOD

Similarly, the Pb207/!!236 age is obtained by multiplying the chemical weight percent of total lead by the 

corrected atom percent abundance of radiogenic Pb207 

and dividing by the chemical weight percent of total 

uranium multiplied by the atom percent abundance of 

U235 . The conversion factor of weight to atom percent, 

1.1 540, is used to change the lead-uranium ratio to an 

atomic ratio. The Pb207/!!235 age thus becomes

The Pb^/Th232 age thus becomes

From the tables read 950 ±2 1. 3 million years.

Pb2°VPb2M AGE METHOD

The age calculated from the Pb^/Pb206 ratio may be 

obtained directly from the isotopic composition of the 

remaining radiogenic Pb206 and Pb207 . The Pb207/Pb206 

age thus becomes

NmlNtot -,

From the tables read 950 ±71.9 million years.

Pb«»/Th232 AGE METHOD

The Pb208/Th232 age is obtained by multiplying the 

total chemical weight percent of lead by the atom percent abundance of remaining radiogenic Pb208 and dividing by the total chemical weight percent of thorium 

times 100. This ratio is converted to an atomic 

ratio by using the following factor: 

232.111 206.32 ~ L1250°'

From the tables read 950 ±46. 8 million years.

Physical isotopic masses were calculated from data 

given by Huizenga (1955) and by Sullivan (1957).

LITERATURE CITED

Fleming, E. H., Jr., Ghiorso, A., and Cunningham, B. B., 1952,

The specific alpha-activities and half -lives of U284 , U23 ", and

U236 : Phys. Rev., v. 88, p. 642-652. 

Holmes, Arthur, 1931, Radioactivity and geological time, pt. 4

of The age of the earth: Natl. Research Council Bull. 80,

p. 124-459. 

Huizenga, J. R., 1955, Isotopic masses A>201: Physica, v. 21,

p. 410-424. 

Keevil, N. B., 1939, The calculation of geological age: Am. Jour.

Sci., v. 237, p. 195-214. 

Kovarik, A. F., 1931, Calculating the age of minerals from radioactivity data and principles, pt. 3 of The age of the earth:

Natl. Research Council Bull. 80, p. 73-123. 

Kovarik, A. F. and Adams, N. I., Jr., 1938, The disintegration

constant of thorium and the branching ratio of thorium C:

Phys. Rev., v. 54, p. 413-421. 

 1955, Redetermination of the disintegration constant of

U238 : Phys. Rev., v. 98, p. 46. 

Kulp, J. L., Bate, G. L., and Broecker, W. S., 1954, Present

status of the lead method of age determination: Am. Jour.

Sci., v. 252, p. 345 365. 

Nier, A. O., 1950, A redetermination of the relative abundances

of the isotopes of carbon, nitrogen, oxygen, argon, and

potassium: Phys. Rev., v. 77, p. 789. 

Rosholt, J. N., 1958, Radioactive disequilibrium studies as an

aid in understanding the natural migration of uranium and

its decay products: United Nations Internat. Conf. Peaceful Uses of Atomic Energy, 2d, Geneva, 1958, Proc. v. 2,

Survey of raw material resources, p. 230-236. 

Senftle, F. E., Farley, T. A., and Lazar, N., 1956, Half-life of

Th282 and the branching ratio of Bi2U : Phys. Rev., v. 104,

p. 1629.

Senftle, F. E., Stieff, L. R., Cuttitta, Frank, and Kuroda, P. K., 

1957, Comparison of the isotopic abundance of U236 and U238

and the radium activity ratios in Colorado Plateau uranium

ores: Geochim. et Cosmochim. Acta, v. 11, p. 189-193. 

Sullivan, W. H., 1957, Trilinear chart of nuclides: U. S. Government Printing Office, Washington 25, D. C. 

Wickman, F. E., 1939, Some graphs on the calculation o* geological age: Sveriges Geol. Undersokning Arsbok, v. 33,

no. 7, p. 1-8.

TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

[Numbers above tables are the ages, in millions of years, that are given on each page]

TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

1-50

11

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.000153

0.000307

0.000461

0.0006i4

0.000768

0.000922

0,001075

0.001229

0.001383

0.001537

0.001691

0.001845

0.001998

0.002153

0% 0023o7

0.002462

0.002615

0.002769

0.002924

0.003077

0.003232

0.003386

0.003540

0.003694

0.003849

0.00400 2

0.004157

0.004312

0.004466

0,004620

0.004775

0.004930

0.005083

0,005238

0.005393

0.005547

0.005702

0.005857

0.0060io

0.006165

0.006320

0.006475

0.006629

0.006784

0.006939

0.007093

0.007249

0.0074o4

0.007558

0.007713

Age

Number 

of 

years

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

Error

+

0.0

0,0

0,0

0.0

0.0

0,0

0.0

0,0

0.0

0.0

0,0

0.0

0,0

0,0

0,0

0.0

0.0

0.0

0,0

0.0

0,0

o.o

0.1

0.1

0.1

0,1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0,1

0.1

N 207/N235

Ratio

0.000972

0.001945

0.002920

0.003895

0.004871

0.005849

0.006828

0.007807

0.008787

0.009768

0.010750

0.011733

0.012717

0.013702

0.014688

0.015674

0.0166&2

0.017651

0.018642

0.019633

0.020624

0.021616

0.022609

0.023605

0.0246oo

0.025597

0.026595

0.027593

0.028592

0.029593

0.030594

0.031597

0.0326oo

0.033605

0.0346o9

0.0356i6

0.036622

0.037632

0.038641

0.039651

0.040662

0.041674

0.042687

0.043702

0.044716

0.045732

0.046749

0.047767

0.048787

0.0498o7

Age

Number 

of 

years

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

Error 

±

0.0

0.0

0.1

0.1

0.1

0.1

0.2

0.2

0.2

0.2

0.2

0.3

0.3

0.3

0.3

0.4

0.4

0.4

0.4

0,4

0.5

0.5

0.5

0,5

0.6

0.6

0.6

0.6

0.7

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0,8

0.9

0.9

0.9

0.9

0.9

1.0

1.0

1,0

1,0

1.1

1.1

XI

XI

"2077*206

Ratio

0.045955

0.045974

0.045993

0.0460i2

0,046030

0.046049

0.046068

0.046087

0.046106

0.046124

0.046143

0.046162

0.046181

0.0462oo

0.0462i9

0.046237

0.046256

0.046275

0.046294

0.046313

0.046337

0.046361

0.046380

0.046399

0.0464i7

0.046436

0.046455

0.046474

0.046493

0.0465i3

0.046532

0.046551

0.046570

0.046589

0.046607

0.046626

0.046645

0.046664

0.046682

0.0467oi

0.046720

0.046739

0.046758

0.046777

0.046796

0.0468i5

0.046834

0.046853

0.046872

0.046891

Age

Number 

of 

years

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

Error 

+

558

55.2

55.2

55.2

55.1

55.1

55.1

55.1

55.1

55.1

56.6

56,7

57,7

56.7

56.6

55.6

56.5

56.6

55.8

56.9

56.3

56.3

56.4

56.6

56,1

56.9

56.4

56.0

56.3

56.5

56.2

56.0

56.6

56.4

56.1

56.4

56,2

56.1

56.8

56.5

56.4

56.3

56,6

56.5

56.3

56.6

56.2

56,1

56,5

56.5

N2 08/^2 3 2

Ratio

0.000048

0.000097

0.000146

0.000195

0.000244

0.000292

0.000341

0.000390

01000439

0.000488

0,000536

0,000585

0.000634

0.000683

0.000732

0.000781

0.000829

0,000878

0.000927

0.000976

0.001025

0.001073

0.001122

0.001171

0,001220

0.001269

0.001317

0.001366

0.001416

0.001465

0.001514

0.001563

0.00l6ii

0.001660

0.001709

0.001758

0.001807

O.OOlSss

0.001904

0.001953

0.0020o3

0.00205 2

0.0021oo

0.002149

0.002198

0.002247

0.002296

0.002345

0.002393

0.002442

Age

Number 

of 

years

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

Error 

+

o.o

0,1

0.1

0.2

0,2

0.3

0.3

0.4

0.4

0.5

0.5

0.6

0.6

0.7

0.7

0.8

0.8

0.9

0.9

xo

xo

XI

XI

X2

X2

X3

1,3

X4

X4

X5

X5

X6

X6

X7

X7

X8

X8

X9

X9

2.0

2.0

2.1

2,1

2.2

2.2

2.3

2,3

2.4

2,4

2.5
12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

51-100

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.007868

0.008022

0.008178

0.008333

0.008488

0.008643

0.008798

0.008953

0.0091o8

0.009263

0.009418

0.009573

0,009728

0.009884

0,010038

0.010194

0.010350

0.010505

0.010660

0.010815

0.010971

0.011126

0.011281

0.011437

0.011592

0.011748

0.011904

0.012058

0.0l22i4

0.012370

0.012526

0.012681

0.012837

0.012993

0.013148

0.013304

0.013460

0.013615

0.013771

0.013927

0.014082

0.014238

0.014395

0.014551

0.014706

0.014862

0,0l50i9

0.015174

0.015330

0.015487

Age

Number 

of 

years

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

Error 

±

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.2

0,2

0,2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0,2

0.2

0.2

0,2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

^207/^235

Ratio

0.050829

0,051850

0.052873

0.053897

0.054922

0.055947

0.056976

0.0580o3

0.059032

0.060063

0.061093

0.062125

0.063159

0.064193

0.065228

0.066264

0.0673oi

0.068339

0.069378

0.070418

0.071459

0.0725oi

0.073545

0.074589

0.075634

0.076681

0.077727

0.078775

0.079825

0.080875

0.081926

0.082979

0.084032

0.085086

0.086142

0.087198

0.088255

0.0893i5

0.090374

0.091434

0.092496

0.093558

0.094621

0.095687

0.096753

0.097819

0.098887

0.099956

0.101025

0,102096

Age

Number 

of 

years

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

Error

+

11

12

12

12

12

13

13

13

13

13

1.4

14

14

14

15

15

15

15

15

16

16

16

16

17

17

17

1.7

18

18

18

18

18

19

19

19

19

2,0

2.0

2.0

2.0

2.0

2.1

2.1

2.1

2.1

2.2

2.2

2.2

2.2

2.2

N 207/N206

Ratio

0.0469io

0,046929

0,046948

0.046967

0,046986

0.047005

0.047024

0.047043

0.047062

0.047081

0.0471oo

0,0471i9

0,047138

0.047157

0.047176

0,047196

0.047216

0.047243

0.047264

0,047284

0.0473oi

0.047322

0.047344

0.047361

0.047383

0.0474oi

0.047418

0.047443

0,047462

0,047479

0.047498

0.047520

0.047538

0.047557

0.047579

0.047598

0.047616

0.047640

0,047658

0,047677

0.0477oo

0.047719

0.047735

0,047755

0.047778

0.047798

0.047815

0.047838

0.047857

0,047874

Age

Number 

of 

years

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

Error 

±

56.6

56,7

56.4

56.4

56.5

56.4

56.5

56.5

56.5

56.6

56.6

56,7

56,8

56.7

56,9

56.8

56.6

56.7

56.8

56.9

56.7

56.8

56.9

56.9

56.9

56.9

56.8

57.0

57.0

56.9

56.9

57.0

57.0

56.9

57.1

57.0

56.9

57,1

57.0

57,1

57.2

57.2

57.1

57.1

57.3

57.3

57.2

57.3

57.3

57.2

^208/^232

Ratio

0.002492

0.002541

0.002590

0.002638

0.002687

0.002736

0.002785

0.002835

0.002883

0,002932

0,0029ai

0.003030

0.003079

0.003128

0.003177

0.003226

0.003275

0,003324

0.003373

0.003421

0.003471

0.003520

0.003569

0.003618

0.003667

0.003715

0.003765

0.0038i4

0.003863

0.0039i2

0.003960

0.0040io

0.004059

0.0041oa

0.004157

0.004205

0.004255

0.0043o4

0.004353

0.0044o2

0.004451

0, 0045oo

0,004549

0.004598

0.004647

0.004696

0.004745

0.004794

0.004843

0.004892

Age

Nurrber 

of 

years

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

Error 

+

2.5

2.6

2.6

2.7

2.7

2,8

2.8

2.9

2.9

3.0

3.0

3.1

3.1

3.2

3,2

3.3

3,3

3,4

3.4

3.5

3.5

3,5

3.6

3.6

3,7

3.7

3.8

3.8

3.9

3.9

4.0

4.0

4.1

4,1

4.2

4.2

4,3

4,3

4.4

4,4

4.5

4.5

4,6

4.6

4.7

4.7

4.8

4.8

4.9

4,9
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

101-150

13

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0,015642

0,015798

0,015955

0.0161io

0.016267

0.016423

0,016580

0.016735

0,016892

0.017048

0.0172o4

0.017361

0.0175i7

0.017673

0.017830

0.017986

0.018142

0.018299

0.018457

0.0186i4

0.0187&9

0.018926

0.019083

0.019239

0.019396

0.019553

0.019709

0.0198&6

0.020023

0.020179

0.020336

0.020493

0.020650

0.0208o7

0.020964

0.021121

0.021277

0.021434

0,021592

0.021748

0.0219o5

0.022063

0.0222i9

0.022376

0.022534

0.022691

0.022848

0.0230ns

0.023163

0.023320

Age

Number 

of 

years

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

Error 

+

0.2

0.2

0.2

0,2

0.2

0,2

0.2

0.2

0,2

0.2

0.2

0,2

0.3

0.3

0.3

0,3

0.3

0.3

0,3

0.3

0.3

0,3

0,3

0.3

0.3

0.3

0.3

0,3

0.3

0.3

0,3

0,3

0,3

0.3

0.3

0.3

0.3

0,3

0,3

0.3

0,3

0.3

0.3

0.3

0,3

0,3

0.3

0.3

0.3

0.3

"207/^235

Ratio

0.103168

0.104242

0.105316

0.106391

0.1074&6

0.108543

0,109622

0.110701

0,111782

0.112862

0.113945

0.115028

0.1161i3

0.117199

0.118285

0.119372

0.1204&1

0.121551

0.122643

0.123734

0.124827

0.125922

0.1270i6

01281ii

0.1292io

0.130309

0.131407

0.132508

0.133609

0.1347ii

0.135815

0.136921

0.138026

0.139133

0,140241

0.1413sn

0.1424&0

0.143572

0.144684

0,145797

0.1469ii

0.148027

0.149143

0.1502&1

0.151380

0.152499

0.153621

0.154742

0.1558&5

0.156989

Age

Number 

of 

years

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

Error 

+

2.3

2,3

2,3

2.3

2.4

2.4

2.4

2.4

2.4

2.5

2.5

2.5

2.5

2.6

2.6

2,6

2.6

2.6

2.7

2,7

2.7

2.7

2.8

2.8

2.8

2.8

2.8

2.9

2.9

2.9

2.9

3.0

3.0

3.0

3.0

3.1

3.1

3.1

3.1

3.1

3.2

3.2

3.2

3.2

3.3

3.3

3,3

3.3

3.3

3.4

^207/^206

Ratio

0.047898

0.0479i8

0.047936

0.047959

0.047976

0.047997

0, 0480is

0.048038

0.048057

0,048077

0.048098

0.048116

0.048137

0.048159

0.048177

0.048198

0,048220

0.048238

0.048255

0.048274

0.048298

0.048317

0,048336

0.048358

0.048378

0.048397

0.0484i9

0.048439

0.048458

0.048480

0.0485oo

0,048521

0.048540

0.0485&0

0.048581

0.0486oi

0,048623

0.048644

0.0486&2

0.048685

0.048705

0,048723

0.048746

0.0487&7

0.048786

0.048806

0.048827

0.048848

0.0488&7

0.048888

Age

Number 

of 

years

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

Error 

+

57.4

57.5

57.3

57.5

57.3

57.4

57.3

57.5

57.4

57,4

57.5

57.4

57.5

57.7

57.6

57.6

57.7

57.6

57.4

57.4

57.6

57.5

57.5

57.6

57.6

57.6

57.7

57.7

57.6

57.7

57.8

57.8

57.7

57.8

57.8

57.8

57.9

57,9

57.8

58.0

57,9

57.8

58.0

58,1

58.0

58.0

58.0

58.1

58.1

58.0

N208/

Ratio

0,004942

0,004990

0.0050,39

0,005088

0.005138

0.005187

0.005236

0.005284

0,005334

0,005383

0,005432

0,005481

0.005530

0.005579

0.005628

0.005678

0.005727

0.005775

0,005824

0.005874

0.005923

0.005972

0.006022

0006070

0.0061i9

0,006168

0.0062i8

0.0062&7

0,0063i5

0.006365

0.0064i4

0.0064&3

0.0065i3

0.006561

0.0066io

0.0066&0

0.006709

0.006758

0.006808

0.006856

0,0069o5

0.006955

0.007004

0.007053

0.007102

0.007151

0.0072oo

0.007250

0.007299

0.007348

//V 232

Age

Number 

of 

years

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

Error 

+

5.0

5,0

5.1

5,1

5,2

5.2

5.3

5,3

5.4

5,4

5.5

$5

5,6

5.6

5.7

5.7

5.8

5.8

5.9

5,9

6,0

6.0

6.1

6,1

6.2

6.2

6.3

6,3

6.4

6.4

6.5

6.5

6.6

6.6

6,7

6.7

6.8

6.Q

6,9

6.9

7.0

7.0

7.0

7.1

7.1

7,2

7.2

7.3

7.3

7,4

485342 O 59-
14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

151-200

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.023478

0.023635

0,023792

0.023950

0, 024107

0,024264

0.024422

0.024579

0.024736

0.024894

0.025052

0.025209

0.025366

0,025524

0.025682

0.025839

0.025997

0.026155

0.0263i2

0.026470

0.026629

0.026786

0.026944

0.027102

0.027260

0.0274i7

0.027576

0.027734

0.027891

0.028049

0.028207

0.028365

0.028523

0.028681

0.028839

0.028997

0.029155

0.029315

0.029472

0.029631

0.029789

0.029947

0.0301Q5

0.030264

0.030422

0.030580

0.030739

0.030896

0.031055

0.0312i4

Age

Number 

of 

years

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

Error 

±

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.4

0.4

0.4

0,4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0,4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

*207/"235

Ratio

0,158116

0.159241

0.160369

0,161497

0162627

0.163758

0.164890

0.166023

0.1671,57

0.168293

0.169429

0.170566

0.171706

0.172844

0.173985

0.175127

0.1762&9

0.1774i4

0.178560

0.179707

0.180853

0.1820o2

0.183151

0.184302

0.185453

0.186607

0.187762

0.1889i7

0.190073

0.191231

0.192387

0.193549

0.1947io

0.195871

0.197034

0.198199

0.199364

0.200531

0.201698

0.202867

0.204036

0.205207

0.206379

0.207554

0.208729

0.209904

0.211081

0.212259

0.213438

0.2146i7

Aee

Number 

of 

years

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

Error 

±

3.4

3.4

3.4

3.5

3.5

3.5

3.5

3.5

3.6

3.6

3.6

3.6

3.7

3.7

3.7

3.7

3.7

3.8

3.8

3.8

3.8

3.9

3.9

3.9

3.9

3.9

4.0

4.0

4.0

4.0

4.1

4.1

4.1

4.1

4.2

4.2

4.2

4.2

4.2

4.3

4.3

4,3

4.3

4.4

4.4

4.4

4.4

4.4

4.5

4.5

N 207/

Ratio

0.048908

0.048928

0.048950

0.048969

0.048990

0.0490i2

0.049031

0.049053

0.049075

0.049095

0.0491i4

0,049136

0.049158

0.049178

0.049198

0.049220

0.049240

0.049260

0.049282

0.049303

0.049321

0.049344

0.049364

0.049384

0,049405

0.049428

0.049447

0,049468

0,049490

0.0495H

0.049531

0.049553

0.049574

0.049595

0.049616

0.049638

0.049659

0.049677

0.0497oo

0.049720

0.049741

0.049762

0.049784

0.049804

0.049826

0.049848

0,049868

0.049891

0.0499i2

0.049932

'*206

Age

Number 

of 

years

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

Error 

±

58.0

58.0

58.1

58,0

58.1

58.2

58.1

58.2

58.3

58.2

58.2

58.3

58.4

58.3

58.3

58.4

58.3

58.3

58.4

58.5

58.3

58.4

58.4

58.4

58.4

58,5

58.4

58.4

58.6

58.6

58.5 sa6

58.6

53,6

58.6

58.7

58.7

58.6

58.7

58.7

58.7

58.7

58.8

58.7

58.8

58.8

58.8

58,9

58.9

58.8

^208/^232

Ratio

0.007397

0.007446

0.007495

0.007545

0.007594

0.007642

0,007692

0.007741

0.007791

0.007840

0.007888

0.007938

0.007987

0.008037

0.008086

0.008135

0.008184

0.008233

0.008283

0.008332

0.008381

0.008430

0,008479

0.008529

0.008578

0.008627

0.008676

0.008725

0.008775

0.008824

0.008874

0.008923

0.008971

0.009021

0,009070

0.009120

0.-009169

0.0092i8

0.009267

0.0093i7

0.009366

0.0094i5

0,009464

0,0095i3

0,009563

0.0096i2

0.009662

0.0097ii

0.009760

0, 009809

Age

Number 

of 

years

151

15?

153

154

155

15<>

157

153

159

160

161

16?

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

1PO

in

1P2

183

1P4

1P5

1M

1P7

1PB

1P9

190

191

192

193

194

195

196

197

198

199

200

Error 

+

7.4

7.5

7,5

7.6

7,6

7,7

7.7

7.8

7.8

7.9

7.9

8.0

8.0

8.1

8.1

8.2

8.2

8.3

8.3

8.4

8.4

8.5

8.5

8.6

8.6

a7

8.7

8.8

8.8

8.9

8.9

9.0

9.0

9.1

9.1

9.2

9.2

9.3

9.3

9,4

9.4

9.5

9.5

9.6

9.6

9.7

9.7

9.8

9.8

9.9
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

201-250

15

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.031373

0.031530

0,031690

0.031849

0.0320o7

0.032166

0.032325

0.032482

0.032641

0,0328oo

0.032958

0.0331i7

0.033276

0.033435

0.033594

0.033754

0.0339i3

0.034071

0.034230

0,034389

0.034547

0.0347o7

0.0348&6

0.035024

0.035183

0.035343

0.035503

0.0356&1

0,035821

0.035980

0.036139

0.036298

0.036458

0.0366i6

0.036776

0.036935

0.037095

0.037254

0.0374i4

0.037574

0.037732

0.037892

0.03805 2

0.0382ii

0.038370

0.038530

0.038690

0.038850

0.0390io

0.039169

Age

Number 

of 

years

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

Error 

±

0.4

0.4

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0,5

0.5

0.5

0,5

0.5

0.5

0.5

0.5

0,5

0.5

0.6

0.6

^207/^235

Ratio

0.2158oo

0.216982

0.2181&6

0.219350

0.220536

0.221722

0.2229i3

0.2241oi

0.225291

0.226484

0.227676

0.228870

0.230066

0.2312&3

0,232460

0.2336&0

0.234858

0.236060

0.2372&2

0.2384&6

0.2396&9

0.240875

0.242083

0.243291

0.2445oo

0.2457H

0.246922

0.248134

0.249348

0.250564

0.251779

0.252998

0.2542i6

0.255436

0.256658

0.257879

0.259103

0.260328

0.261554

0.262780

0.2640o8

0.265238

0.2664&9

0.2677oi

0.268934

0.270168

0.271403

0.272639

0.273878

0.275116

Aee

Number 

of 

years

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

Error 

+

4.5

4.5

4.6

4.6

4.6

4,6

4.6

4.7

4.7

4.7

4.7

4,8

4.8

4.8

4.8

4.8

4,9

4.9

4.9

4.9

5.0

5.0

5.0

5.0

5,0

5.1

5.1

5.1

5.1

5.2

5.2

5,2

5.2

5.3

5.3

5.3

5.3

5.3

5.4

5.4

5.4

5,4

5,5

5.5

5.5

5.5

5.5

5,6

5,6

5.6

"207/^206

Ratio

0.049952

0.049976

0.049995

0.0500i5

0.050038

O.OSOOss

0.050079

0.050103

0.050124

0.050145

0.050167

0.050188

0.050209

0.050230

0.050251

0.050271

0.050292

0.050315

0.050337

0,050358

0.050381

0.0504oi

0.050422

0.050445

0.050467

0.050487

0.050508

0.050531

0.050551

0.050573

0.050595

0.050617

0.050637

0.050661

0.050682

0.050704

0.050725

0.050747

0.050768

0.050789

0.050812

0.050833

0.050855

0.050877

0.0509oo

0,050921

0.050942

0.050963

0.050985

O.OSlOos

Age

Number 

of 

years

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

Error 

+

58.8

59,0

58.9

sas

59,0

58.9

58.9

59,1

59.1

59.0

59,1

59,1

59.1

59.1

59.1

59.0

59.0

59.2

59.2

59.2

59,3

59.2

59,2

59.3

59.3

59.2

59.3

59.4

59,3

59.3

59,4

59,4

59.4

59.5

59.5

59,5

59.5

59,5

59.5

59.5

59,6

59.5

59.6

59.6

59,7

59.7

59,6

59,6

59,6

59.7

N208/

Ratio

0.009859

0.009908

0.009958

0.010006

0.010056

0.010105

0.010155

0,010204

0.010253

0,010302

0.010352

0.010401

0.010451

0.0105oo

0.010549

0,010598

0.010648

0,010697

0,010747

0.010795

0,010845

0.010894

0.010944

0.010993

0.011043

0.011091

0.011141

0.011190

0.011240

0.011290

0.011338

0.011388

0.011437

0,011487

0.011536

0.011585

0.011634

0.011684

0.011734

0.011783

0.011833

0.011881

0.011931

0,011980

0.012030

0.012080

0.012128

0.012178

0.012227

0.012277

^232

Age

Number 

of 

years

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

Error 

+

9.9

10.0

10.0

10,1

10.1

10.2

10.2

10,3

10,3

10.4

10.4

10,5

10,5

10.5

10.6

10.6

10.7

10.7

10.8

10.8

10.9

10.9

11,0

110

111

1L1

11.2

112

11.3

113

11.4

114

11.5

115

116

116

117

117

118

11.8

119

119

12.0

12.0

12.1

121

12.2

12.2

123

12.3
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

251-300

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

"206/^238

Ratio

0.039329

0.039489

0.039648

0.039807

0.039968

0.040129

0.040288

0,040448

0.040608

0.040767

0^040927

0,041087

0.041246

0.041408

0.0415&8

0.041728

0.041887

0.042048

0.042208

0.0423&7

0,042529

0.042689

0.042849

0.043009

0.043170

0.043329

0.043490

0.043650

0.0438i2

0.043971

0.044132

0.044293

0.044452

0.0446i3

0.044775

0.044935

0.045095

0.045256

0.0454i6

0.045577

0.045738

0.0459oo

0.046059

0.046220

0.046381

0.046541

0.046702

0.0468&3

0.047024

0.047185

Age

Number 

of 

years

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

Error

±

0.6

0.6

0.6

0.6

0.6

0,6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0,6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0,6

0.6

0.6

0.6

0.7

0.7

0.7

0.7

0.7

0.7

0.7

N 207/N235

Ratio

0.276357

0.277599

0.278841

0.280084

0.281330

0.282575

0.283825

0.285072

0.286322

0.287574

0.288825

0.290078

0.291335

0,292590

0.293847

0,295106

0296365

0.297625

0.298889

0.300152

0.3014i6

0.302681

0.303948

0.305216

0.306486

0,307757

0.309030

0.310302

0.311577

0.312852

0.314128

0.315407

0.316687

0.317968

0,319249

0.320532

0.3218i7

0.323102

0.324390

0.325678

0.3269&7

0.328258

0.329549

0.330844

0.332138

0.333433

0.334729

0.336027

0337327

0.338627

Age

Number 

of 

years

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

Error 

±

5.6

5.7

5.7

5.7

5.7

5.7

5.8

5.8

5.8

5.8

5.9

5.9

5.9

5.9

5.9

6.0

6,0

6.0

6,0

6.1

6.1

6.1

6.1

6.1

6.2

6,2

6.2

6.2

6.3

6.3

6.3

6.3

6.4

6.4

6.4

6.4

6,4

65

6,5

6,5

6.5

6.6

6.6

6.6

6.6

6.6

6.7

6.7

6.7

6.7

"207/N206

Ratio

0.051029

0.051051

0.051074

0,051096

0.0511i7

0.051137

0.051161

0.051182

0.051204

0.051227

0.051249

0.051271

0.051295

0.0513i4

0.051336

0.051358

0.051382

0.051403

0.051425

0.051449

0.051469

0.051491

0.0515i3

0.051536

0.051557

0.051581

0.051603

0.051625

0.051646

0,051670

0.051691

0.0517i3

0,051737

0.051759

0.051779

0.0518o2

0,051825

0.051847

0.051871

0.051892

0.0519i4

0.051936

0.051960

0.051982

0.052 Oo 4

0.052028

0.05205 o

0.052072

0.052095

0.0521i7

Age

Number 

of 

years

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

Error

+

59.7

59,7

59.8

59,8

59.7

59.7

59.8

59.8

59.8

59.8

59.9

59.9

60.0

59.9

59.9

59,9

60.0

60.0

60.0

60,1

60.0

60,0

60.0

60.1

60% 0

60.1

60,2

60.2

60.1

60.2

60,1

60.2

60.3

60.3

60.2

60.2

60.3

60.3

60.4

60.3

60.3

60.3

60,4

60.4

60.4

60.5

60.5

60.5

60.5

60,5

^208/^232

Ratio

0.012327

0.012375

0.012425

0,012474

0.012524

0.012574

0.012623

0.012672

0.012721

0.012771

0.012821

0.012870

0,0129i9

0.0129&9

0.0130i8

0.0130&8

0.013117

0.013166

0.0132i6

0.0132&5

0.013315

0.013365

0.0134i4

0.013463

0.013513

0.013562

0.013612

0.013662

0.0137io

0.0137&0

0.0138io

0.013859

0.013909

0.013958

0.014007

0,014057

0,014107

0.014156

0.014206

0.014255

0,014304

0,014354

0.014404

0.014453

0,014502

0.014552

0,0146o2

0.014651

0, Ol47oi

0.014751

Age

Numl °r 

of 

years

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

2£1

2£<l

2£3

2£4

2£5

2£6

287

2£8

2 £0

2<50

291

292

2S3 2<54

295

2<56

297

298

2co

3CO

Error 

+

12.4

12.4

12.5

12.5

12.6

12,6

12.7

12,7

12.8

12.8

12.9

12.9

13.0

13.0

13.1

13.1

13.2

13,2

13.3

13,3

13.4

13.4

13.5

13.5

13.6

13.6

13-7

13,7

13.8

13.8

13.9

13,9

14.0

14.0

14.0

14.1

14.1

14.2

14.2

14.3

14.3

14.4

14.4

14.5

14.5

14.6

14,6

14-7

14.7

14.8
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

301-350

17

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

N 206/N 238

Ratio

0.047347

0.047507

0.047668

0.047829

0.047990

0.048151

0.0483i3

0.048474

0.048634

0.048796

0.048958

0.0491i8

0.049280

0.049441

0.0496oi

0.049764

0.049925

0.050086

0.050247

0.0504o9

0.050570

0.050732

0.050894

0.051055

0.0512i6

0.051378

0.051540

0.0517oi

0.051863

0.052025

0.052185

0.052348

0.0525io

0.052672

0.052833

0.052995

0.053158

0.053319

0.053481

0.053643

0.053804

0.053967

0.054129

0.054290

0.054452

0.0546i5

0.054778

0.054939

0.0551oi

0.0552&3

Age

Number 

of 

years

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

Error 

+

0.7

0.7

0.7

0,7

0.7

0.7

0.7

0.7

0.7

0,7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0,7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

"2077*235

Ratio

0.339930

0.341234

0.342537

0.343843

0.345151

0.346459

0.347769

0.349080

0.350393

0.351705

0.353022

0.354336

0.355654

0.356973

0.358293

0.3596i3

0.360935

0.362259

0.363584

0.3649ii

0.366238

0.367568

0.368898

0.370228

0.371561

0.372896

0.374231

0.375567

0.376905

0.378244

0.379584

0.380928

0.382270

0.383615

0.384959

0.386306

0.387654

0,389004

0.390356

0.391708

0.3930&2

0.3944i6

0.395773

0,397131

0.398489

0.399849

0.4012ii

0.402574

0.403939

0.405303

Age

Number 

of 

years

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

Error 

+

6.8

6.8

6.8

6.8

6.8

6.9

6.9

6.9

6.9

7,0

7.0

7.0

7.0

7.0

7.1

7.1

7,1

7.1

7.2

7,2

7.2

7.2

7.2

7.3

7.3

7.3

7.3

7.4

7.4

7.4

7.4

7.5

7.5

7.5

7.5

7.5

7.6

7.6

7.6

7.6

7.7

7.7

7.7

7.7

7.7

7.8

7.8

7.8

7.8

7.9

N 207/

Ratio

0.052139

0.052162

0.052185

0.052207

0.052230

0.052253

0.052274

0.052297

0.052321

0.052343

0.0523&5

0.052389

0.0524H

0.052434

0.052458

0.052479

0.052502

0.052525

0.052548

0.052570

0.052594

0.0526i6

0.052638

0.052661

0.052685

0.052708

0.052730

0.052753

0.052776

0.052799

0.052823

0.052845

0.052868

0.052891

0.0529i4

0.052937

0.052959

0.052983

0.0530o6

0.053029

0.053053

0.053075

0.053098

0.053122

0.053145

0.053167

0.053190

0.0532i4

0.053238

0.053261

/N206

Age

Number 

of 

years

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

Error 

+

60.5

60.5

60.6

60.6

60.6

60.6

60,6

60.6

60.7

60.7

60.7

60.7

60.7

60,8

60.8

60.8

60.8

60.8

60.8

60.8

60.9

60.9

60.9

60.9

6X0

61.0

61.0

61.0

61.0

61.0

61.1

61.1

61.1

61,1

61.1

61.1

611

612

61.2

612

61.2

61.2

61.2

61.2

61.3

61.3

6X2

61.3

6X3

6X3

N208/

Ratio

0.014799

0.014849

0.014899

0.014949

0.014998

0.015047

0.015097

0.015147

0.015196

0.015246

0.015295

0.015344

0.015394

0,015444

0.015494

0.015543

0.015592

0.015642

0.015692

0.015741

0.015791

0.015840

0.015890

0.015940

0.015989

0.016039

0.016088

0.016138

0.016187

0.016237

0.016287

0.016337

0.016386

0.016435

0.016485

0.016535

0.016585

0.016634

0.016683

0.016733

0.016783

0.016833

0.016882

0.016931

0.016981

0.017031

0.017081

0.017131

0.017180

0.017229

^232

A^e

Number ~ 

, Error of +

years

301 14.8

302 14.9

303 14.9

304 15.0

305 15.0

306 15.1

307 15.1

308 15.2

309 15.2

310 15.3

311 15.3

312 15.4

313 15.4

314 15.5

315 15.5

316 15.6

317 15.6

318 15.7

319 15.7

320 15.8

321 15.8

322 15.9

323 15.9

324 16,0

325 16.0

326 16.1

327 16.1

328 16.2

329 16.2

330 16.3

331 16.3

332 16.4

333 16.4

334 16.5

335 16.5

336 16.6

337 16.6

338 16.7

339 16.7

340 16.8

341 16.8

342 16.9

343 16.9

344 17.0

345 17.0

346 17.1

347 17.1

348 17.2

349 17.2

350 17.3
18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

351-400

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

N 206/N 238

Ratio

0.055426

0.055588

0.055750

0.0559i2

0.056075

0.056237

0.056399

0.056561

0.056724

0.056887

0.057049

0.0572ii

0.057374

0.057536

0.057699

0.057862

0.058023

0.058187

0.058350

0.058511

0.058674

0.058838

0.0590oi

0.059162

0.059325

0.059489

0.059651

0.059814

0,059977

0,060140

0.060303

0.060466

0.060628

0.060792

0,060955

0.061118

0,061281

0.061444

0.061608

0.061770

0.061934

0,062097

0.062260

0,062423

0.062587

0.062750

0.062913

0.063077

0.063241

0.063403

Age

Number 

of 

years

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

Error

±

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0,8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0,8

0.8

0.8

0.8

0,8

0.8

0,9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

"207

Ratio

0.406671

0.408040

0.409408

0.410780

0.412151

0.413524

0.4149oo

0.416276

0.417655

0.419032

0.4204i3

0.421794

0.423178

0.424562

0.425947

0.427333

0.428722

0.4301io

0.431501

0.432895

0.434289

0.435683

0.437080

0.438477

0.439876

0.441277

0.442680

0.444082

0,445486

0,446892

0.448301

0.449708

0.4511i9

0.452530

0.453943

0.455356

0.456771

0.458190

0.459609

0.461028

0.462449

0.463870

0.465294

0.466718

0.468147

0.469575

0.471004

0.472435

0.473866

0.4753oo

/"235

Ae

Number 

of 

years

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

e

Error

±

7.9

7.9

7.9

7.9

8.0

8.0

8.0

8.0

8.1

8.1

8.1

8.1

8.1

8.2

8,2

8.2

8.2

8,3

8,3

8.3

8,3

8.3

8.4

8.4

8.4

8,4

8.5

8.5

as

8.5

8.5

8.6

8.6

8.6

8.6

8.7

8.7

8.7

8,7

8.8

8.8

8.8

8.8

8.8

8.9

8.9

8.9 a9

9.0

9.0

N 2Q7/N206

Ratio

0.053283

0.053307

0.053330

0.053354

0.053376

0.0534oo

0.053424

0.053447

0.053470

0.053493

0.053517

0.053541

0.053564

0.053587

0.0536io

0.053633

0.053658

0.053680

0.053704

0.053729

0,053752

0.053774

0.053798

0.053823

0,053846

0.053869

0.053893

0.0539i7

0.053940

0.053964

0.053987

0.0540ii

0.054036

0.054058

0.054082

0.054106

0.054130

0.054154

0.054177

0.0542o2

0.054225

0.054248

0.054273

0.054297

0.054320

0.054344

0.054368

0.054392

0.054415

0.054440

Age

Number 

of 

years

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

Error 

+

6X4

6X4

6X4

6X4

6X4

6X4

61,5

6X5

6X5

6X5

6X6

6X6

61.6

6X6

6X6

6X6

6X7

6X6

6X6

6X7

6X7

6X6

6X7

6X8

6X8

6X8

6X8

6X9

6X8

6X8

6X9

6X9

6X9

6X9

6X9

62.0

62.0

62.0

62.0

62,0

62.0

62.0

62.1

62.1

62.1

62.1

62.2

62.2

62.2

62.2

N208/N2 3 2

Ratio

0,017279

0.017329

0.017379

0,017428

0.017478

0.017527

0.017577

0.017627

0.017677

0.017726

0.017776

0.017826

0.017875

0.017925

0.017974

0.018024

0.018074

0,018124

0.018174

0.018223

0.018272

0.018322

0.018373

0.018423

0,018473

0.018522

0.018572

0.018622

0.018672

0.018722

0.018770

0.018820

0.018870

0,018920

0.018970

0.0190i9

0.019069

0.019119

0.019169

0.019219

0.019269

0.019318

0,019367

0.019417

0.019467

0.019517

0.019566

0.019616

0.0196&6

0,019716

Age

Number 

of 

years

351

35?

353

354

355

356

357

358

359

360

361

36?

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

3PO

3P1

3P?

3P3

3P4

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

Error 

+

17.3

17.4

17.4

17.5

17.5

17.5

17.6

17,6

17.7

17.7

17.8

17.8

17.9

17,9

18.0

18.0

18.1

18.1

18.2

18,2

18,3

18,3

18,4

18.4

18,5

18.5

18.6

18,6

18,7

1817

18,8 ias

18,9

18.9

19.0

19.0

19,1

19.1

19,2

19,2

19,3

19.3

19,4

19,4

19.5

19,5

19.6

19.6

19,7

19.7
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

401-450

19

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.063568

0.063731

0.063894

0.064057

0,064222

0.064384

0.064548

0.0647i3

0.064875

0.065039

0.065204

0.0653&7

0.065530

0.065694

0.065859

0.066021

0.066185

0.066350

0.0665i3

0.066677

0.066842

0.0670o5

0.0671&9

0.067334

0,067498

0.0676&1

0.067826

0.067990

0.068153

0.068318

0,068482

0.068646

0.0688ii

0.068975

0.069138

0.069304

0.0694&8

0.069632

0.069797

0.0699&1

0.070125

0.070290

0.070454

0.0706i9

0.070783

0.070948

0.0711i3

0.071277

0.071441

0.071607

Age

Number 

of 

years

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

Error 

+

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0,9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

0.9

10

1.0

10

10

10

1.0

10

10

1.0

1.0

1.0

1,0

1.0

10

1.0

1.0

1.0

1.0

10

1,0

1.0

XO

^207/^235

Ratio

0,476737

0.478171

0.479608

0.481049

0.482489

0.483930

0.485374

0.486820

0.488265

0.489712

0.491160

0.4926io

0.4940&3

0.495516

0.496971

0.498427

0.499885

0.501344

0,502804

0.5042&7

0.505729

0.507192

0.508653

0.510126

0.511595

0.513065

0.514537

0,5160o9

0,517485

0.518960

0,520437

0.5219i7

0.523398

0,524878

0.5263&1

0.527845

0.529333

0.530821

0.532309

0.5338oo

0.535291

0.536784

0538278

0.539774

0.541275

0.542773

0.544273

0.545774

0.547277

0.548782

Age

Number 

of 

years

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

Error

+

9.0

9.0

9.0

9.1

9.1

9.1

9.1

9.2

9.2

9.2

9.2

9.2

9.3

9.3

9.3

9.3

9.4

9.4

9.4

9.4

9.4

9.5

9.5

9.5

9,5

9.6

9.6

9.6

9.6

9.6

9.7

9.7

9.7

9.7

9.8

9.8

9.8

9.8

9.9

9.9

9.9

9.9

9.9

10.0

10.0

100

10.0

10.1

10.1

10.1

W 207/

Ratio

0.054463

0.054487

0.054512

0.054536

0,054559

0.054584

0.054608

0.054631

0,054656

0.054680

0.054703

0.054728

0.054753

0.054776

0.0548oo

0.054825

0.054849

0.054873

0,054898

0.054922

0.054945

0.054970

0.054994

0.0550i8

0.055042

0.0550&8

0.055091

0.055116

0.055141

0.0551&5

0.055189

0.0552i4

0.055238

0.0552&2

0.055288

0.055311

0.055336

0.055361

0.055385

0.0554io

0.055434

0.055459

0.055483

0.055508

0.055533

0,055557

0.055581

0.055607

0.055632

0.055655

'W 206

Age

Number 

of 

years

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

Error 

+

62.2

62.2

62.3

62.3

62.3

62.3

62.4

62.3

62.4

62.4

62.3

62.4

62.5

62.4

62.5

62.5

62.5

62.5

62.6

62.6

62.5

62.6

62.6

62.6

62.6

62.7

62.7

62.7

62.7

62.7

62.7

62,8

62.8

62,8

62,9

62.8

62.8

62.9

62.9

62.9

62.9

62,9

62.9

63.0

63.0

63.0

63.0

63.1

63.1

63.0

N208/N232

Ratio

0,019766

0,019815

0.0198&5

0.0l99i5

0.0199&5

0, 0200i5

0.020065

0.0201i4

0.0201&4

0,0202i4

0,020264

0.020314

0.0203&3

0.0204i3

0.0204&3

0.020513

0.0205&3

0, 020612

0.0206&2

0.0207i2

0.0207&2

0.0208i2

0.0208&2

0.020911

0.020961

0.0210ii

0.0210&1

0.021111

0.021160

0.0212io

0.0212&0

0,0213io

0.0213&0

0, 0214io

0.021459

0,0215o9

0,021559

0.021609

0.021659

0.021708

0.021758

0.021808

0.021858

0, 0219o8

0.021957

0.022007

0.022058

0, 022108

0.022158

0.0222o8

AgNumber 

of

years

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

Error 

+

19.8

19.8

19.9

19.9

20.0

20.0

20,1

20,1

20,2

20.2

20L3

20.3

20.4

20.4

20.5

20,5

20.6

20.6

20,7

20.7

20,8

20.8

20.9

20.9

21.0

21.0

21.0

21,1

21.1

21.2

21.2

21.3

21.3

21.4

21.4

21.5

21.5

21.6

21.6

2X7

21.7

21,8

2X8

21.9

2X9

22.0

22.0

22,1

22.1

22.2
20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

451-500

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.071771

0.071935

0.0721oi

0.072266

0.072430

0.072595

0.0727&1

0.072926

0,073091

0.073256

0.073420

0.073585

0.073751

0,0739i5

0,074080

0.074246

0.0744H

0.074576

0.074741

0.074906

0.075072

0,075237

0.075403

0.0755&7

0.075732

0.075898

0.0760&3

0.076229

0.076394

0.076560

0,076725

0,076890

0.077057

0.077221

0.077388

0.077553

0.077718

0.077884

0.078050

0.078215

0.078381

0.078547

0.078713

0.078878

0.079044

0.0792io

0,079376

0.079542

0.079708

0.079873

Age

Number 

of 

years

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

Error

±

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0 1.1

u

1.1 1.1 1.1

u

1.1

1.1 1.1 1.1 1.1 1.1

1.1 1.1

u

1.1

u

u

1.1 1.1

u

1.1

1.1

u

1.1 1.1 1.1

^207/^235

Ratio

0.550289

0.551797

0.553307

0.5548i8

0.556330

0.557843

0.5593&0

0.560875

0.562392

0.5639i3

0.565433

0.566957

0.568481

0.570007

0.571533

0.573060

0.574592

0.576123

0.577656

0.579191

0.580727

0.582264

0.583803

0.585343

0.586885

0.588429

0.589974

0.591520

0.5930&9

0,5946i7

0.596168

0.597722

0.599276

0.600832

0.602389

0.603947

0.605507

0.607069

0.608632

0.610197

0.611761

0.613330

0.614898

0.6164&9

0.618043

0.6196i7

0.621191

0.622767

0.624346

0.625927

Aee

Number 

of 

years

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

Error

±

10.1

10.1

10.2

10.2

10.2

10.2

10.3

10.3

10.3

10,3

10.3

10,4

10.4

10.4

10.4

10.5

10.5

10.5

10.5

10,5

10.6

10.6

10.6

10.6

10.7

10.7

10.7

10J

10.7

10.8

10.8

10.8

10.8

10.9

10.9

10.9

10.9

11.0

11.0

11.0

HO

11.0

11.1

HI

11.1

11.1

11.2

11.2

1X2

U2

W 207/W206

Ratio

0.055681

0.055706

0.055730

0.055754

0.055780

0,055804

0.055828

0.055853

0.055878

0.055902

0.055928

0.055953

0.055977

0.056003

0.056028

0.056052

0.056077

0.056102

0.056127

0.056152

0.056177

0.056202

0.056226

0.056252

0.056278

0.056302

0.056328

0.056352

0.056378

0.056402

0.056428

0.056454

0.056478

0.056504

0.056528

0.056554

0.056580

0.056605

0.056630

0.056656

0.056680

0.056706

0.056731

0.056757

0.056782

0.056807

0.056833

0.056858

0.056883

0.0569io

Age

Number 

of 

years

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

Error 

+

63.1

63.1

63.1

63.1

63.2

63.2

63.1

63,2

63.2

63.2

63.2

63.3

63.2

63.3

63.3

63.3

63.3

63.3

63.4

63.4

63.4

63.4

63.4

63.4

63.5

63.5

63.5

63.5

63.5

63.5

63.6

63.6

63.6

63.6

63.6

63.7

63.7

63.7

63.7

63.8

63.7

63.8

63.8

63.8

63.8

63.8

63.9

63.9

63.9

63.9

N208/N232

Ratio

0.022257

0.022307

0.022357

0.022407

0.022457

0,022506

0.022556

0.022606

0.022656

0.022707

0,022756

0.022806

0.022856

0.022906

0.022956

0.023006

0.02305 5

0.023105

0.0231.56

0.023*07

0.023257

0.023306

0.023356

0.023406

0.023456

0.023506

0.023556

0.023606

0.023656

0.023706

0.023756

0.023806

0.023855

0.0239o6

0,023956

0.0240o6

0.024056

0.024105

0.024155

0.024206

0.024256

0.0243o6

0.024355

0.0244o5

0.024455

0.024506

0.024556

0.024606

0.024655

0.024705

Age

Number 

of 

years

451

452

453

454

455

456

457

458

459

460

461

4*2

463

464

465

466

467

4*8

469

470

471

472

473

474

475

476

477

478

479

480

481

432

433

434

435

436

437

488

439

490

491

492

493

494

495

496

497

498

499

500

Error 

+

22,2

22.3

22.3

22.4

22.4

22.5

22.5

22.6

22,6

22.7

22.7

22,8

22.8

22,9

22.9

23.0

23.0

23.1

23.1

23.2

23.2

23.3

23.3

23.4

23.4

23.5

23.5

23.6

23.6

23.7

23.7

23.8

23.8

23.9

23.9

24,0

24.0

24.1

24.1

24.2

24.2

24.3

24.3

24,4

24.4

24.5

24.5

24.5

24.6

24.6
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

502-600

21

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

"2067*238

Ratio

0.080206

0.080538

0.080870

0.081202

0.081534

0.081868

0.0822oo

0.082532

0.082866

0,083198

0,083532

0.083864

0.08419?

0.084531

0.0848&4

0.085198

0.085531

0.085865

0.086199

0.086532

0.086866

0.087202

0.087535

0.087870

0.088204

0.088538

0.088873

0.089208

0.089544

0.089878

0.0902i3

0.090548

0.090883

0.0912i8

0.091555

0.091890

0.092226

0.092561

0.092896

0.093234

0.0935&9

0.093906

0.094241

0.094577

0.0949i5

0.095251

0.095587

0.095925

0.096261

0.096598

Age

Number 

of 

years

502

504

506

508

510

512

514

516

518

520

522

524

526

528

530

532

534

536

538

540

542

544

546

548

550

552

554

556

558

560

562

564

566

568

570

572

574

576

578

580

582

584

586

588

590

593

594

596

598

600

Error 

±

1.1

1.1

1.1

XI

1.1

1.1 1.1

XI

XI

1.2

X2

1.2

X2

X2

X2

X2

X2

X2

1.2

X2

1.2

1.2

1.2

1.2

X2

X2

1.2

1.2

X2

X2

1.2

1,3

X3

X3

X3

X3

X3

X3

X3

X3

X3

X3

X3

1.3

X3

X3

X3

X3

X3

X3

N 207/N235

Ratio

0.629090

0.6322&2

0.635436

0.638621

0.641809

0.645005

0.648207

0.651415

0.654627

0.657850

0.661075

0.664306

0.667547

0.670792

0.674043

0.677303

0.680568

0.683837

0.687116

0.690399

0.693688

0.696984

0.700288

0.703595

0.7069ii

0.710233

0.713561

0.716895

0.720240

0.723585

0.726939

0.730301

0.733669

0.737042

0.740425

0.7438io

0.747203

0.750605

0.7540i2

0.757425

0.760847

0.764272

0.767706

0.771147

0,774595

0.778049

0.781509

0.784976

0.788450

0.791929

Age

Number 

of 

years

502

504

506

508

510

512

514

516

518

520

522

524

526

528

530

532

534

536

538

540

542

544

546

548

550

552

554

556

558

560

562

564

566

568

570

572

574

576

578

580

582

584

586

588

590

592

594

596

598

600

Error 

+

1X3

1X3

1X4

1X4

1X4

1X5

1X5

1X6

1X6

1X7

1X7

1X8

11.8

1X8

1X9

1X9

12.0

12.0

12.1

12.1

12.2

12.2

12.3

12.3

12.3

12.4

12.4

12.5

12.5

12.6

12.6

12.7

12.7

12.7

12.8

12.8

12.9

12.9

13.0

13.0

13.1

13.1

13.2

13.2

13.2

13.3

13.3

13.4

13.4

13.5

^207/^206

Ratio

0.0569&0

0.0570ii

0.057062

0.057113

0.057165

0.0572i5

0.057267

0.057319

0.057369

0.057422

0.057473

0.057525

0.057577

0.057628

0.057680

0.057732

0.057784

0.057836

0.057888

0.057941

0.057993

0.058044

0.058097

0.058149

0.058202

0.058255

0.058307

0.058360

0.0584i2

0.058465

0.058518

0.058571

0.058625

0.058678

0.058730

0.058784

0.058837

0.058891

0.058945

0.058997

0.059051

0.059104

0.059159

0.0592i3

0.059266

0.059320

0.059374

0.059427

0.059482

0.059536

Age

Number 

of 

years

502

504

506

508

510

512

514

516

518

520

522

524

526

528

530

532

534

536

538

540

542

544

546

548

550

552

554

556

558

560

562

564

566

568

570

572

574

576

578

580

582

584

586

588

590

592

594

596

598

600

Error 

+

63.9

64.0

64.0

64.0

64.1

64.1

64.2

64.2

64.2

64.2

64.3

64.3

64.4

64.3

64.4

64.4

64.5

64.5

64.6

64,6

64.7

64.6

64.7

64.7

64.8

64.8

64.8

64.9

64.9

64.9

65.0

65.0

65.1

65.1

65.1

65.1

65,2

65.2

65.3

65.3

6"5.3

65.3

65.4

65.5

65.5

65.5

65.5

65,6

65,6

65,6

N20B/N2 3 2

Ratio

0.024806

0.024905

0.025006

0.025106

0.025205

0.025306

0.025406

0.025506

0.025606

0.025706

0.025806

0.025907

0.0260o6

0.026107

0.026207

0.026307

0.026407

0.026507

0.026608

0.026709

0.026808

0.026909

0.0270io

0.027109

0.0272io

0.027309

0.0274io

0.0275ii

0.0276io

0.0277ii

0.0278i2

0.0279ii

0.0280i2

0.028112

0.0282i3

0.028313

0.0284i3

0.028514

0.028615

0.0287i4

0.028815

0.0289i6

0.0290i6

0.029116

0.029216

0.0293i8

0.0294i9

0.029519

0.0296 2 o

0.029720

Age

Number 

of 

years

502

504

506

508

510

512

514

516

518

520

522

524

526

528

530

532

534

536

538

540

542

544

546

548

550

552

554

556

558

560

562

564

566

568

570

572

574

576

578

580

582

584

586

588

590

592

594

596

598

600

Error 

+

24.7

24.8

24.9

25.0

25.1

25.2

25.3

25.4

25.5

25.6

25.7

25.8

25.9

26.0

26,1

26.2

26,3

26.4

26.5

26.6

26.7

26,8

26.9

27.0

27,1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28.0

28.1

28.2

28.3

28.4

28.5

28.6

28.7

28.8

28.9

29.0

29.1

29.2

29,3

29.4

29.5

29.6
22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

602-700

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.096936

0.097273

0.0976ii

0.097947

0.098285

0.098623

0.098961

0.099299

0.099636

0.099974

0.100313

0.100650

0.100990

0.101327

0.101666

0.102005

0.102344

0.102682

0.103022

0.103360

O.l037oo

0.104039

0.104379

0.104719

0.105058

0.105398

0.105738

0.106077

0.106418

0.106757

0.107097

0.107439

0.107778

0.108120

0.108459

0.1088oo

0.109142

0.109482

0.109824

0.110165

0.110506

0.110848

0.111189

0.111531

0.111872

0.1122i4

0.112557

0.112898

0.113240

0.113583

Age

Number 

of 

years

602

604

606

608

610

612

614

616

618

620

622

624

626

628

630

632

634

636

638

640

642

644

646

648

650

652

654

656

658

660

662

664

666

668

670

672

674

676

678

680

682

684

686

688

690

692

694

696

698

700

Error 

±

1.3

13

13

1.3

14

14

14

1,4

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

16

"207/^235

Ratio

0,7954i7

0.7989ii

0.8024i3

0.805921

0,809436

0.812957

0.816486

0.820020

0.823562

0.827113

0.830667

0.834231

0.8378oi

0.841377

0.844961

0.848552

0.852150

0.855754

0.859365

0.862985

0.866611

0.870242

0.873884

0,877529

0.881183

0.884846

0.888513

0.892189

0.895872

0.899561

0.903257

0.906963

0.910673

0.914392

0.918117

0.921850

0.925591

0.929339

0.933094

0.936855

0.940627

0.944403

0.948186

0.951979

0,955778

0.959585

0.963397

0.967220

0.971047

0.974883

Age

Number 

of 

years

602

604

606

608

610

612

614

616

618

620

622

624

626

628

630

632

634

636

638

640

642

644

646

648

650

652

654

656

658

660

662

664

666

668

670

672

674

676

678

680

682

684

686

688

690

692

694

696

698

700

Error 

+

13,5

13.6

13.6

13.6

13.7

13.7

13.8

13.8

13.9

13.9

14.0

14.0

14.0

14.1

14.1

14,2

14.2

14.3

14.3

14.4

14.4

14.5

14.5

14.5

14.6

14.6

14.7

14.7

14.8

14.8

14.9

14.9

14.9

15,0

15.0

15.1

15.1

15.2

15.2

15.3

15.3

15.3

15.4

15,4

15.5

15.5

15.6

15.6

15.7

15.7

N 207/N206

Ratio

0.059590

0.059644

0.059698

0.059754

0.059808

0.059862

0.0599i7

0.059971

0.060026

0.060081

0.060136

0.060191

0.060246

0.0603oi

0.060356

0.0604ii

0.060467

0.060523

0.060577

0.060634

0.060689

0.060744

0.0608oo

0.060855

0.0609i2

0.060967

0.061023

0.061080

0.061135

0.061192

0.061249

0.061304

0.061361

0.061417

0.061474

0.061531

0.061587

0.061644

0.0617oi

0.061758

0.061815

0.061872

0.061929

0.061986

0.062044

0.0621oi

0.062158

0.0622i6

0.062273

0.062331

Age

Number 

of 

years

602

604

606

608

610

612

614

616

618

620

622

624

626

628

630

632

634

636

638

640

642

644

646

648

650

652

654

656

658

660

662

664

666

668

670

672

674

676

678

680

682

684

686

688

690

692

694

696

698

700

Error 

+

65.7

65.7

65.7

65.8

65.8

65.8

65.9

65.9

66,0

66.0

66,0

66,1

66.1

66.1

66.1

66.2

66,2

66.3

66.3

66.4

66,4

66,4

66,4

66,4

66.5

66,5

66.6

66,6

66,6

66.7

66.7

66,7

66.8

66,8

66.9

66,9

66.9

67.0

67.0

67.0

67.1

67.1

67.1

67.2

67,2

67.3

67.3

67.3

67.3

67.4

N208/N232

Ratio

0.029820

0.029921

0.030021

0.030122

0.030223

0.030323

0.030424

0.030525

0.030624

0.030725

0.030825

0.030926

0.031027

0.031127

0.031228

0.031329

0.031429

0.031530

0.031631

0.031732

0,031834

0.031934

0.032035

0.032136

0.032236

0.032337

0.032437

0.032538

0.032639

0.032739

0.032841

0,032942

0.033042

0.033143

0.033243

0.033344

0.033446

0.033546

0,033648

0.033749

0.033850

0.033951

0.034051

0.034152

0.034254

0.034354

0.034455

0.034557

0.034657

0.034758

Age

Number 

of 

years

602

604

606

608

610

612

614

616

618

620

622

624

626

628

630

632

634

636

638

640

642

644

646

648

650

652

654

656

658

6*>Q

6^)2

6*4

6%6^)8

670

672

674

676

678

6BO

6B2

6Q4

6B6

688

690

692

694

696

698

700

Error 

+

29.7

29.8

29.9

30.0

30.1

30.2

30.3

30,4

30,5

30.6

30.7

30.8

30.9

310

311

312

313

314

315

31,5

316

317

31.8

319

32.0

32,1

32,2

32.3

32.4

32.5

32.6

32,7

32.8

32.9

33.0

33.1

33.2

33.3

33.4

33.5

33.6

33.7

33.8

33.9

34.0

34.1

34.2

34.3

34.4

34.5
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

702-800

23

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

N 206//V 238

Ratio

0.113925

0.114268

0.114609

0.114952

0.115295

0.115638

0.115981

0.116325

0.116667

0.1170n

0.117354

0.117697

0.118042

0.118385

0.118729

0.11907 3

0.1194i6

0.1197^1

0.120105

0.120449

0.120795

0.121139

0.121484

0.121829

0.122173

0.122518

0.122863

0.123208

0.123553

0.123898

0.124244

0.124589

0.124934

0.125283

0,125628

0.125974

0.126320

0.1266&5

0.1270i2

0.127359

0.127705

0.12805 2

0.128398

0.128746

0.129093

0.129440

0.129787

0.130135

0.130483

0.130829

Age

Number 

of 

years

702

704

706

708

710

712

714

716

718

720

722

724

726

728

730

732

734

736

738

740

742

744

746

748

750

752

754

756

758

760

762

764

766

768

770

772

774

776

778

780

782

784

786

788

790

792

794

796

798

800

Error 

±

1.6

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

17

18

18

18

18

18

18

^207/^235

Ratio

0.978729

0.982578

0.986437

0.990304

0.994176

0.998057

1001947

1005842

1009744

1013659

1017577

1021502

1025439

1029379

1033328

1037288

1041251

1045224

1.049203

1053191

1057189

1061191

1065203

1069223

1073249

1077288

1081328

1085377

1089439

1093504

1097578

1101661

1105752

1109849

1113957

1118071

1122190

1126322

1.130459

1134607

1.138763

1142923

1.147094

1.151270

1155459

1159653

1163857

1168070

1172287

1176515

Age

Number 

of 

years

702

704

706

708

710

712

714

716

718

720

722

724

726

728

730

732

734

736

738

740

742

744

746

748

750

752

754

756

758

760

762

764

766

768

770

772

774

776

778

780

782

784

786

788

790

792

794

796

798

800

Error 

±

15.8

15.8

15.8

15.9

15.9

160

16.0

16.1

16.1

16.2

162

16.2

16.3

16.3

16.4

16.4

16.5

16.5

16.6

16.6

16.7

16.7

16.7

16.8

16.8

16.9

16.9

170

17.0

17.1

171

17.1

17.2

17.2

17.3

17.3

17.4

17.4

17.5

17.5

17.5

17.6

17.6

17.7

17.7

17,8

17.8

17.9

17.9

18.0

^207/^206

Ratio

0.062389

0.062446

0.062505

0.062563

0.062620

0.062678

0.062737

0.062794

0.062853

0,0629ii

0.062970

0.063028

0.063086

0.063145

0.063204

0.063263

0,063322

0.063381

0.063440

0.063499

0.063557

0.063617

0.063676

0.063735

0,063795

0.063855

0.0639i 4

0.063974

0.064034

0.064094

0.064154

0.0642i4

0.064275

0,064333

0.064394

0.064454

0.064514

0.064576

0,064636

0.064696

0.064757

0.064818

0.064879

0.064939

0.0650oo

0.065061

0.065123

0.065183

0.065244

0.065306

Age

Number 

of 

years

702

704

706

708

710

712

714

716

718

720

722

724

726

728

730

732

734

736

738

740

742

744

746

748

750

752

754

756

758

760

762

764

766

768

770

772

774

776

778

780

782

784

786

788

790

792

794

796

798

800

Error 

±

67.4

67.4

67.5

67.6

67,6

67.6

67.6

67.6

67.7

67.7

67.8

67.8

67.8

67.9

67.9

68.0

68.0

68.0

68.1

68.1

68.1

68.1

6a2

68.2

68.3

68.3

68.3

68.4

68.4

68.4

68.5

68.5

68,6

68.6

68.6

68.7

68.7

68.8

68.8

68.8

68.9

68.9

68.9

68.9

69.0

69.0

69.1

69.1

69.1

69.2

^208/^232

Ratio

0.034859

0,034960

0.035061

0.035162

0.035263

0.035364

0.035466

0,035567

0,035669

0,035769

0,035871

0,035971

0.03607 2

0,036174

0,036274

0.036376

0.036477

0,036578

0,036679

0,036780

0,036881

0.036983

0,037084

0.037186

0.037288

0,037388

0,037490

0,037590

0.037692

0,037794

0,037894

0,037996

0,038098

0,038198

0,0383oo

0,0384oi

0,0385o2

0,0386o5

0,038706

0,0388o7

0.038909

0, 0390io

0,0391i2

0,03 92 12

0.039314

0,0394i6

0.0395i7

0.0396i8

0,039720

0.039821

Age

Number 

of 

years

702

704

706

708

710

712

714

716

718

720

722

724

726

728

730

732

734

736

738

740

742

744

746

748

750

752

754

756

758

760

762

764

766

768

770

772

774

776

778

780

782

784

786

788

790

792

794

796

798

800

Error 

±

34.6

34.7

34.8

34.9

35.0

35.1

35.2

35.3

35.4

35.5

35.6

35.7

35.8

35.9

36.0

36.1

36.2

36.3

36.4

36.5

36.6

36.7

36.8

36.9

37.0

37.1

37.2

37.3

37.4

37.5

37,6

37.7

37.8

37.9

38.0

38.1

38.2

38.3

38.4

38.5

38.5

38.6

38.7

38.8

38.9

39.0

39.1

39.2

39.3

39.4
24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

802-900

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.131177

0.131525

0.131872

0,132220

0.132568

0.132917

0.133266

0.133614

0.1339&2

0.1343H

0.134660

0.135009

0.135357

0.135706

0.136056

0.136405

0.136753

0.137104

0.137453

0.137803

0.138153

0.138501

0.138852

0.1392oi

0.139554

0.139904

0.140253

0.140605

0.140955

0.141304

0.141656

0.142007

0.142359

0.1427io

0.143061

0.143413

0.143763

0.144116

0.144467

0.144819

0.145172

0.145523

0.145875

0.146228

0.146580

0.146933

0.147285

0.147637

0.147992

0.148344

Age

Number 

of 

years

802

804

806

808

810

812

814

816

818

820

822

824

826

828

830

832

834

836

838

840

842

844

846

848

850

852

854

856

858

860

862

864

866

868

870

872

874

876

878

880

882

884

886

888

890

892

894

896

898

900

Error

±

1.8

1.8

1.8

1.8

X8

1.8

X8

1,8

X8

1.8

1.8

1.8

1,8

1.8

1.8

X8

X8

X9

19

1.9

1.9

19

X9

1.9

1.9

X9

1.9

19

1.9

1.9

1.9

X9

1.9

1.9

1.9

1.9

1.9

X9

1.9

2.0

2.0

2.0

2,0

2,0

2.0

2.0

2.0

2.0

2.0

2.0

"207/^235

Ratio

1.180752

1.184996

1.189248

1.1935io

1,197777

1.202055

1.206341

1,210636

1214937

1.219249

1.223569

1.227894

X232233

1,236576

1.240929

X245290

1.249659

1.254037

3,258423

1,262819

X267223

1,271635

1.276058

1,280486

1.284925

1289373

1293826

X298291

1,302766

1307246

1.311735

X316237

1.320745

1.325260

1,329788

1.334321

3,338864

1.343416

1.347976

1,352546

U57126

X361713

X366308

1.3709i2

1.375528

1.380152

1.384783

1,389426

1,394075

1,398732

Aee

Number 

of 

years

802

804

806

808

810

812

814

816

818

820

822

824

826

828

830

832

834

836

838

840

842

844

846

848

850

852

854

856

858

860

862

864

866

868

870

872

874

876

878

880

882

884

886

888

890

892

894

896

898

900

Error 

+

18.0

18.0

18.1

18.1

18.2

18.2

18.3

18.3

18.4

18.4

18.4

18.5

18.5

18.6

18.6

18.7

18.7

18.8

18.8

18.8

18.9

18.9

19.0

19,0

19.1

19.1

19.2

19.2

19.3

19.3

19.3

19.4

19.4

19.5

19.5

19.6

19.6

19.7

19.7

19.7

19,8

19.8

19,9

19.9

20.0

20.0

20.1

20.1

20.2

20.2

N 207/N2Q6

Ratio

0.065368

0,065429

0.065491

0.065553

0.065615

0.065676

0.065738

0.0658oo

0.0658&2

0.065924

0.065986

0.066048

0.0661ii

0.066174

0,066236

0.066298

0.0663&2

0,066424

0.066487

0.066550

0.066612

0.066676

0.066739

0.066803

0.0668&5

0.066929

0.066993

0, 067055

0.067120

0.067184

0.067247

0.0673H

0.067375

0.067439

0.067503

0.0675&7

0.067632

0.067696

0.067760

0.067825

0.067889

0.0679 5 4

0,0680i9

0.06808 4

0.068149

0.0682i4

0.068279

0,068344

0.068409

0.068474

Age

Number 

of 

years

802

804

806

808

810

812

814

816

818

820

822

824

826

828

830

832

834

836

838

840

842

844

846

848

850

852

854

856

858

860

862

864

866

868

870

872

874

876

878

880

882

884

886

888

890

892

894

896

898

900

Error 

+

69.2

69.2

69,3

69.3

69.4

69.4

69.4

69.5

69,5

69,5

69.5

69.6

69.6

69.7

69.7

69,7

69,8

69.8

69.9

69.9

69.9

70.0

70.0

70.1

70,1

70.1

70.1

70.1

70.2

70.3

70.3

70.3

70.4

70.4

70.4

70.5

70.5

70.5

70.6

70.6

70.6

70.7

70.7

70.8

70,8

70.8

70.9

70.9

70.9

71.0

N208/

Ratio

0.039923

0,040025

0.040126

0,040228

0.040329

0.040431

0,040533

0.040634

0,040736

0.040837

0,040938

0,041040

0.041141

0,041243

0.041346

0.041447

0.041549

0.041650

0.041752

0.041854

0.041955

0.042057

0.042159

0,042260

0,042362

0.0424&3

0.042566

0.042668

0.042770

0.042872

0.042974

0.043075

0,043177

0,043279

0.043380

0.043482

0.043584

0.043687

0.043789

0.043890

0.043992

0.044095

0.044196

0.044298

0.044399

0.0445oi

0.044604

0,044705

0.044808

0.0449H

^232

Age

Nurrber 

of 

years

802

804

806

808

810

812

814

816

818

820

822

824

826

828

830

832

834

836

838

£40

842

£44

£46

£48

£50

£52

£54

£56

ess

f<SO

f^2

FM

f*>6

f68

f70

T72

P74

P76

P78

PRO

F82

P84

P86

P88

P90

P92

P94

P96

P98

900

Error 

±

39.5

39.6

39.7

39.8

39.9

40.0

40.1

40.2

40.3

40.4

40.5

40.6

40.7

40.8

40,9

41.0

411

412

41.3

41.4

41.5

41.6

4X7

41.8

43,9

42.0

42.1

42.2

42,3

42.4

42,5

42.6

42.7

42,8

42.9

43,0

43.1

43.2

43.3

43,4

43.5

43.6

43,7

43.8

43.9

44.0

44.1

44.2

44.3

44.4
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

902-1000

25

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0,148695

0.149049

0.149402

0.149756

0.150109

0.150463

0.150817

0.151170

0.151526

0.151879

0.152232

0.152587

0.152942

0.153295

0.153650

0.154004

0.154360

0.154715

0.155069

0.155425

0.155780

0.156135

0.156491

0.156846

0.157202

0.157557

0.1579i3

0.158270

0.158625

0.158982

0.159337

0.159695

0.160052

0.160407

0.1607&5

0.161121

0.161478

0.161836

0.162192

0.162549

0.162907

0.163264

0.163622

0.163980

0.164338

0.164696

0.165054

0.165412

0.165771

0.166129

Age

Number 

of 

years

902

904

906

908

910

912

914

916

918

920

922

924

926

928

930

932

934

936

938

940

942

944

946

948

950

952

954

956

958

960

962

964

966

968

970

972

974

976

978

980

982

984

986

988

990

992

994

996

998

1000

Error 

±

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2,0

2.0

2.0

2.0

2.1

2.1

2.1

2.1

2.1

2,1

2.1

2.1

2.1

2,1

2.1

2.1

2.1

2.1

2.1

2.1

2.1

2,1

2.1

2.1

2.1

2.1

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

^207/^235

Ratio

1,403404

1,408079

1,412767

1,417465

X4221&9

1,426881

1,431607

1,436339

3,441078

1,445831

1,450591

1.455358

1460142

1.464927

1,469722

1.474533

1,479348

1,4841 7 2

1.4890o6

1,493850

1.498706

1.503566

1.508441

1513320

1.518213

1523116

1,528023

1.532944

1.5378/4

1,542813

1,547763

1.552720

1.557689

1.562665

1,567654

1,572651

1,577656

1,582677

1,587702

1,592736

1,597785

1.602840

1,607905

1,612980

1,618067

1,623161

1.628263

1,633384

1.638507

1,643640

Age

Number 

of 

years

902

904

906

908

910

912

914

916

918

920

922

924

926

928

930

932

934

936

938

940

942

944

946

948

950

952

954

956

958

960

962

964

966

968

970

972

974

976

978

980

982

984

986

988

990

992

994

996

998

1000

Error 

+

20.2

20.3

20.3

20.4

20.4

20.5

20.5

20.6

20.6

20.6

20.7

20.7

20.8

20,8

20.9

20.9

21,0

21,0

21,0

21,1

21,1

21.2

21,2

21.3

21.3

21,4

21.4

2X5

21,5

21.5

2X6

2],6

21,7

2X7

2X8

2X8

21.9

2X9

2X9

22.0

22.0

22.1

22.1

22.2

22.2

22.3

22.3

22.4

22.4

22.4

N 207/N206

Ratio

0.068541

0.068606

0.068672

0.068737

0.068803

0.068869

0.068934

0.0690oi

0.069066

0.069133

0.069199

0.0692&5

0.069332

0.069399

0.069465

0.069532

0.069598

0.069665

0.069732

0.069799

0.069866

0.069933

0, 0700oi

0.070068

0.070135

0.070203

0.070271

0.070338

0.070406

0.070474

0.070542

0, 0706io

0.070678

0,070747

0.070814

0.070883

0.070952

0.071020

0.071089

0.071158

0.071227

0,071296

0.071364

0.071433

0.071503

0.071572

0.071641

0,0717n

0,071780

0.071850

Age

Number 

of 

years

902

904

906

908

910

912

914

916

918

920

922

924

926

928

930

932

934

936

938

940

942

944

946

948

950

952

954

956

958

960

962

964

966

968

970

972

974

976

978

980

982

984

986

988

990

992

994

996

998

1000

Error 

+

7X0

7X1

7X1

7X1

7X2

7X2

71.2

7X3

7X3

7X3

7X4

7X4

7X4

7X5

7X5

7X6

7X6

7X6

7X6

7X7

7X7

7X7

7X8

7X8

7X9

7X9

72.0

72.0

72.0

72.1

72.1

72.1

72.2

72.2

72.2

72.3

72.3

72.3

72.4

72.4

72,5

72.5

72.5

72.6

72.6

72.6

72.7

72.7

72.7

72,8

N208/

Ratio

0.0450i2

0.045114

0.045215

0.045318

0.045420

0.045521

0.045624

0.045726

0.045827

0.045931

0.046032

0.046135

0.046237

0.046338

0,046441

0.046543

0.046645

0.046747

0.046849

0.046952

0.047055

0.047156

0.047259

0.047361

0.0474&3

0.047565

0.047667

0.047769

0.047875

0.047974

0.04807 7

0,048180

0,048281

0.048384

0.048485

0.048588

0.048691

0.048793

0.048896

0.048999

0.0491oo

0.049203

0.049305

0.049407

0.0495io

0.049612

0.049716

0.049818

0.049920

0.050023

^232

Age

Number 

of 

years

902

904

906

908

910

912

914

916

918

920

922

924

926

928

930

932

934

936

938

940

942

944

946

948

950

952

954

956

958

960

962

964

966

968

970

972

974

976

978

980

982

984

986

988

990

992

994

996

998

1000

Error 

±

44.5

44.6

44.7

44.8

44.9

45.0

45.1

45.2

45.3

45.4

45.5

45.5

45.6

45.7

45.8

45.9

46,0

46.1

46,2

46,3

46.4

46.5

46,6

46.7

46.8

46.9

47.0

47,1

47,2

47.3

47.4

47,5

47.6

47.7

47.8

47.9

48.0 4ai

48.2

48.3

48.4

48.5

4a6

48.7

48.8

48.9

49.0

49.1

49.2

49.3
26 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

1002-1100

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.166487

0.166846

0.167203

0.167563

0,167922

0.168282

0.168640

0.168999

0.169359

0.169719

0.170078

0.170438

0.170797

0.171158

0.171518

0.171877

0.172238

0.172598

0.172959

0.173320

0.173680

0.174041

0.174402

0.174764

0.175125

0.175485

0.175847

0.176208

0.176570

0.176932

0.177293

0.177655

0.1780i6

0.178380

0.178742

0.179104

0.179466

0.179830

0.180192

0.180556

0.1809i8

0.181281

0.181645

0.182008

0.182372

0.182735

0.183099

0.183463

0.183825

0.184190

Age

Number 

of 

years

1002

1004

1006

1008

1010

1012

1014

1016

1018

1020

1022

1024

1026

1028

1030

1032

1034

1036

1038

1040

1042

1044

1046

1048

1050

1052

1054

1056

1058

1060

1062

1064

1066

1068

1070

1072

1074

1076

1078

1080

1082

1084

1086

1088

1090

1092

1094

1096

1098

1100

Error 

±

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.3

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2.4

2,4

2.4

2.4

2.4

2,4

N 207/N235

Ratio

1,648789

1.653941

1,659107

X664284

1,669469

1,674662

1,679872

1,685084

1,690309

1,695548

1.700791

1,706049

1,711315

1,716592

1,721878

1.727178

1,732483

1.7378oi

1,743129

1,748471

1,753819

1.759177

1,764548

1.769929

1,775320

1,780721

1.786132

1,791553

1,796988

1,802431

1,807885

1,813351

1,818825

1.8243io

1,829808

1,835315

1.840831

1,846363

1,851902

1,857451

I,8630i2

1,868587

1,874168

1,879760

1,885368

1,890980

1,896606

X902248

1,907894

1913552

Age

Number 

of 

years

1002

1004

1006

1008

1010

1012

1014

1016

1018

1020

1022

1024

1026

1028

1030

1032

1034

1036

1038

1040

1042

1044

1046

1048

1050

1052

1054

1056

1058

1060

1062

1064

1066

1068

1070

1072

1074

1076

1078

1080

1082

1084

1086

1088

1090

1092

1094

1096

1098

1100

Error 

+

22.5

22.5

22.6

22.6

22.7

22.7

22.8

22.8

22.8

22.9

22.9

23.0

23.0

23.1

23.1

23.2

23.2

23.2

23.3

23.3

23.4

23.4

23.5

23.5

23.6

23.6

23.7

23.7

23.7

23.8

23.8

23.9

23.9

24.0

24.0

24.1

24.1

24.1

24,2

24.2

24.3

24.3

24.4

24.4

24.5

24.5

24.5

24.6

24.6

24.7

N 207/N206

Ratio

0.071920

0.071989

0.072060

0,072129

0.072199

0.072269

0.072340

0.0724io

0.072480

0.072551

0.072622

0.072692

0.072763

0.072834

0.072905

0.072976

0.073047

0.073119

0.073190

0.073261

0.073333

0.073404

0.073476

0.073547

0.0736i9

0.073692

0.073764

0.073836

0.073908

0.073980

0,074053

0.074125

0.074198

0.074270

0.074343

0.0744i6

0.074489

0.074562

0.074636

0.074708

0.074782

0.074856

0.074929

0.0750o2

0.07507 6

0.075150

0.075224

0.075298

0,075372

0.075446

Age

Number 

of 

years

1002

1004

1006

1008

1010

1012

1014

1016

1018

1020

1022

1024

1026

1028

1030

1032

1034

1036

1038

1040

1042

1044

1046

1048

1050

1052

1054

1056

1058

1060

1062

1064

1066

1068

1070

1072

1074

1076

1078

1080

1082

1084

1086

1088

1090

1092

1094

1096

1098

1100

Error 

+

72.8

72.8

72.9

72.9

73.0

73.0

73.1

73,1

73.1

73.2

73.2

73.2

73.3

73.3

73.4

73.4

73.4

73.5

73.5

73.5

73.6

73.6

73.6

73.7

73.7

73.8

73.8

73.8

73.9

73.9

73.9

74.0

74.0

74.0

74.1

74.1

74.2

74.2

74.2

74.2

74.3

74.4

74.4

74.4

74.4

74.5

74.5

74.6

74.6

74.6

^208/^232

Ratio

0.050126

0.050227

0.050330

0,050432

0.050535

0.050639

0.050740

0.050843

0.050946

0.051048

0.051151

0.051253

0.051356

0.051460

0.051561

0.051664

0.051767

0.051869

0.051972

0.052074

0.052177

0.052281

0.052383

0,052486

0.052589

0.052691

0.052794

0.052896

0.052999

0.053103

0.053205

0.053308

0.0534H

0.053513

0.053616

0.053719

0.053823

0.053926

0.054028

0.054131

0.054234

0.054336

0.054440

0.054542

0.054646

0,054749

0.054851

0.054955

0.055058

0.055160

Age

Number 

of 

years

1002

1004

1006

1008

1010

1012

1014

1016

1018

1020

1022

1024

1026

1028

1030

1032

1034

1036

1038

1040

1042

1044

1046

1048

1050

1052

1054

1056

1058

1060

1062

1064

1066

1068

1070

1072

1074

1076

1078

1080

1082

1084

1086

1088

1090

1092

1094

1096

1098

1100

Error 

+

49.4

49.5

49.6

49.7

49.8

49.9

50.0

50.1

50.2

50.3

50,4

50.5

50.6

50.7

50.8

50.9

51.0

51.1

5X2

5X3

5X4

5X5

5X6

5X7

5X8

5X9

52.0

52.1

52.2

52.3

52.4

52.5

52.5

52.6

52.7

52.8

52.9

53.0

53,1

53.2

53.3

53.4

53.5

53.6

53.7

53.8

53.9

54.0

54.1

54.2
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

1102-1200

27

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.184554

0.1849i8

0.185283

0.185648

0.1860ii

0.186376

0.186740

0.187106

0.187471

0.187836

0.1882oi

0.188567

0.188931

0.189297

0.189661

0.190029

0,190394

0.190759

0.191126

0.191492

0.191859

0.192224

0.192591

0.192959

0.193325

0.193690

0.19405 9

0.194425

0.194793

0,195161

0.195528

0.195896

0.196263

0.196632

0.196999

0.197366

0.197736

0.198103

0.198471

0.198840

0.199208

0.199577

0.199945

0.2003i4

0.200683

0.20105 2

0.201422

0.201791

0.202160

0,202531

Age

Number 

of 

years

1102

1104

1106

1108

1110

1112

1114

1116

1118

1120

1122

1124

1126

1128

1130

1132

1134

1136

1138

1140

1142

1144

1146

1148

1150

1152

1154

1156

1158

1160

1162

1164

1166

1168

1170

1172

1174

1176

1178

1180

1182

1184

1186

1188

1190

1192

1194

1196

1198

1200

Error 

±

2.4

2.4

2.5

2.5

2.5

2,5

2.5

2.5

2.5

2.5

2.5

2.5

2.5

2,5

2.5

2.5

2.5

2.5

2.5

2.5

2.5

2.5

2.5

2.5

2.5

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.6

2.7

2.7

2.7

Ratio

1.919225

1.924905

1.930598

1.936302

1.9420i6

1.947741

1.953480

1.959227

1.964985

1.970758

1.976537

1.982333

1,988138

1.993953

1.999777

2.005615

2.011466

2.017325

2.023197

2.029084

2.034978

2.040884

2.046803

2.052732

2.058672

2.064629

2,070591

2.076567

2.082554

2.088556

2.094564

2.100590

2,106624

2.112667

2,118727

2.124797

2,130878

2.136974

2.1430 77

2.149193

2.155323

2.161464

2.167616

2.173780

2.179961

2.186146

2.192346

2.198562

2.204786

2.211023

^v235.

Age

Number 

of 

years

1102

1104

1106

1108

1110

1112

1114

1116

1118

1120

1122

1124

1126

1128

1130

1132

1134

1136

1138

1140

1142

1144

1146

1148

1150

1152

1154

1156

1158

1160

1162

1164

1166

1168

1170

1172

1174

1176

1178

1180

1182

1184

1186

1188

1190

1192

1194

1196

1198

1200

Error 

±

24.7

24.8

24,8

24.9

24.9

25.0

25.0

25.0

25.1

25.1

25.2

25.2

25.3

25.3

25.4

25.4

25.4

25.5

25.5

25.6

25.6

25.7

25.7

25.8

25.8

25.9

25.9

25.9

26.0

26.0

26,1

26.1

26.2

26.2

26,3

26.3

26.3

26.4

26.4

26.5

26.5

26.6

26.6

26.7

26.7

26.7

26.8

26.8

26.9

26.9

^207/^206

Ratio

0.075521

0.075595

0.075669

0.075744

0.075819

0.075893

0.075969

0.076043

0.076118

0.076193

0,076269

0.076344

0.076420

0,076495

0.076571

0.076646

0.076722

0.076799

0.076874

0.076951

0.077027

0.077103

0.077180

0.077256

0.077333

0.0774io

0.077486

0.077563

0.077640

0.0777i7

0,077794

0.077872

0.077949

0.078026

0.078104

0,078182

0.078259

0.078338

0.0784i6

0.078494

0.078572

0.078650

0.078729

0.078808

0.078886

0.078965

0.079043

0.079123

0.079202

0.079280

Age

Number 

of 

years

1102

1104

1106

1108

1110

1112

1114

1116

1118

1120

1122

1124

1126

1128

1130

1132

1134

1136

1138

1140

1142

1144

1146

1148

1150

1152

1154

1156

1158

1160

1162

1164

1166

1168

1170

1172

1174

1176

1178

1180

1182

1184

1186

1188

1190

1192

1194

1196

1198

1200

Error 

±

74.7

74.7

74.7

74.8

74.8

74.8

74.9

74.9

74.9

75.0

75,0

75.1

75,1

75.2

75.2

75.2

75.2

75.3

75.3

75.4

75,4

75.4

75.5

75.5

75.6

75.6

75.6

75.7

75.7

75.7

75.8

75.8

759

75.9

75.9

76.0

76.0

76,1

76,1

76.1

76,2

76,2

76,2

76.3

76,3

76,4

76,4

76.4

76,5

76,5

N208/N232

Ratio

0.055263

0.055367

0.055470

0.055573

0.055675

0,055779

0.055882

0,055984

0.056089

0.056191

0.056294

0,056398

0,0565oo

0.056603

0.056707

0.0568io

0.056914

0.057016

0,057119

0.057223

0.057325

0.057430

0,057533

0.057636

0.057739

0.057843

0.057945

0.058049

0,058152

0,058256

0,058359

0.058462

0.058565

0.058669

0.058772

0,058876

0,058978

0.059082

0.059186

0.059288

0.059393

0.059497

0.059599

0.059703

0.059806

0.059909

0.0600i3

0,0601i7

0,060220

0.060324

Age

Number 

of 

yearr

1102

1104

1106

1108

me

1112

1114

1116

1118

112 C

1122

1124

1126

1128

113C

1132

1134

1136

1138

114C

1142

1144

1146

1148

use

1152.

1154

1156

1158

116C

1162

1164

1166

1168

117C

1172

1174

1176

1178

118C

1182

1184

1186

1188

119C

1192

1194

1196

1198 12 oe

Error

54,3

54,4

54.5

54.6

54.7

54.8

54.9

55.0

55.1

55.2

55.3

55.4

55.5

55,6

55.7

55.8

55.9

56,0

56,1

56.2

56.3

56.4

56,5

56.6

56,7

56,8

56.9

57.0

57.1

57.2

57.3

57.4

57.5

57.6

57.7

57.8

57.9

58.0

58.1

58.2

58.3

58,4

58,5

58,6

58,7

58,8

58.9

59.0

59,1

59,2
28 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

1202-1300

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.202899

0.203268

0.203640

0,2040o9

0.204379

0.204751

0.205120

0,205490

0.205862

0.206231

0.206603

0.206974

0.207345

0.207716

0.208088

0.208460

0.208830

0.209203

0.209575

0.209945

0.210319

0.210690

0.211062

0.211435

0.211806

0.212181

0.212553

0,212924

0.213298

0.213671

0.214045

0.2144i7

0.214790

0.215165

0.215538

0.2159H

0.216286

0.216658

0.217033

0.217407

0.217780

0.218156

0.218530

0.218905

0.219279

0.219653

0.220030

0.220405

0.220779

0.221155

yv Q.Q

Number 

of 

years

1202

1204

1206

1208

1210

1212

1214

1216

1218

1220

1222

1224

1226

1228

1230

1232

1234

1236

1238

1240

1242

1244

1246

1248

1250

1252

1254

1256

1258

1260

1262

1264

1266

1268

1270

1272

1274

1276

1278

1280

1282

1284

1286

1288

1290

1292

1294

1296

1298

1300

Error 

±

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2,7

2.7

2.7

2.7

2,7

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2.8

2.8

2,8

2.8

2.8

2.8

2.8

2.8

2.8

2.8

2,8

2.8

2.8

2,8

2.8

2,8

2.8

2.8

2,8

2.8

2.8

2,8

2.9

2.9

2.9

2.9

2.9

2,9

2.9

2.9

"207/^35

Ratio

2.217275

2.223534

2.229809

2.236095

2.242392

2.248701

2.255027

2.261361

2.267705

2.274067

2.280439

2.286824

2.293221

2.299630

2.306051

2.312482

2.318934

2.325392

2.3318&0

2.338347

2.344844

2.351355

2.357878

2.364412

2.370959

2.377523

2.384092

2,390678

2.397279

2.403892

2.410516

2.417156

2.423804

2.430469

2.437145

2.443833

2.450534

2.457254

2.463980

2.470720

2.477473

2.484244

2.491026

2.497817

2.504627

2.511448

2.518281

2.525129

2.531988

2.538864

Age

Number 

of 

years

1202

1204

1206

1208

1210

1212

1214

1216

1218

1220

1222

1224

1226

1228

1230

1232

1234

1236

1238

1240

1242

1244

1246

1248

1250

1252

1254

1256

1258

1260

1262

1264

1266

1268

1270

1272

1274

1276

1278

1280

1282

1284

1286

1288

1290

1292

1294

1296

1298

1300

Error 

±

27,0

27.0

27.1

27,1

27.2

27.2

27.2

27.3

27,3

27.4

27.4

27.5

27,5

27.6

27.6

27,6

27.7

27.7

27.8

27.8

27.9

27.9

28.0

28.0

28.1

28.1

28.1

28.2

28.2

28.3

28.3

28.4

28,4

28.5

28.5

28.5

28,6

28.6

28.7

28.7

28.8

28.8

28.9

28.9

28.9

29.0

29,0

29.1

29.1

29.2

N 207/

Ratio

0.079360

0.079440

0.079518

0.079598

0.079678

0.079757

0.079838

0.0799i8

0.079997

0.080078

O.OSOIss

0.080238

0.080319

0.080399

0.080479

0.080560

0.080642

0.080722

0.080803

0.080885

0.0809&5

0.081047

0.081129

0.0812io

0,081292

0.081373

0.081455

0.081538

0.081620

0.081702

0.081784

0.081867

0,081950

0,082032

0.0821i5

0.082198

0,082280

0.082364

0.082447

0.082530

0.082614

0.082697

0.082781

0.082864

0.082949

0,083033

0.0831i6

0,0832oo

0,083285

0.083369

/N

Age

Number 

of 

years

1202

1204

1206

1208

1210

1212

1214

1216

1218

1220

1222

1224

1226

1228

1230

1232

1234

1236

1238

1240

1242

1244

1246

1248

1250

1252

1254

1256

1258

1260

1262

1264

1266

1268

1270

1272

1274

1276

1278

1280

1282

1284

1286

1288

1290

1292

1294

1296

1298

1300

Error

76.5

76,6

76,6

76.7

76.7

76.7

76.8

76,8

76.8

76.9

76.9

76,9

77.0

77.0

77.0

77.1

77.1

77.2

77.2

77,3

77.3

77.3

77.4

77,4

77.4

77.5

77.5

77.5

77.6

77.6

77.7

77.7

77.8

77.8

77.8

77.9

77.9

77.9

78,0

78.0

78.0

78.1

78.1

78,1

78.2

78.3

78.3

78.3

78.4

78.4

N208/

Ratio

0.060427

0.060531

0.060633

0.060738

0.060842

0.060945

0.0610 4 8

0.061152

0.061256

0.061360

0,061463

0.061566

0.061670

0.061773

0.061878

0.061982

0.062085

0.062189

0,062291

0.062395

0.0625oo

0.062603

0.062707

0.0628H

0, 0629i4

0.0630! 9

0.063122

0.063226

0,063330

0.063433

0.063537

0.063642

0.063745

0.063849

0.063952

0.064056

0.064161

0,064264

0.064368

0.064472

0.064576

0.064681

0,064785

0.064888

0,064992

0.065095

0.065199

0,065305

0.065408

0.065512

//v232

Age

Number 

of 

years

1202

12 04

12 OS 120°

1210

1212

1214

1216

1218

1220

1222

1224

1226

1228

1230

1232

1234

1236

123B

1240

1242

1244

1246

1248

1250

1252

1254

1256

1258

1260

1262

1264

1266

1268

1270

1272

1274

1276

1278

1280

1282

1284

12S6

12SB

1290

1292

1294

12*3^

12 co

13CO

Error

59,3

59.4

59.5

59.5

59.6

59.7

59.8

59.9

60.0

60.1

60,2

60.3

60.4

60.5

60.6

60,7

60,8

60,9

6X0

6X1

6X2

6X3

6X4

6X5

6X6

6X7

6X8

6X9

62,0

62.1

62.2

62,3

62,4

62.5

62.6

62.7

62,8

62.9

63,0

63.1

63.2

63.3

63.4

63.5

63,6

63,7

63.8

63.9

64.0

64.1
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

1302-1400

29

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.221530

0.221906

0.222281

0.222656

0.223034

0.223408

0.223786

0.224161

0.224538

0.2249i4

0.225290

0.225667

0.226044

0.226421

0,226798

0.227175

0,227552

0.227931

0.228308

0.228686

0.229064

0.229440

0,229820

0.230196

0,230575

0.230954

0.231332

0.2317H

0.23209 n

0.232467

0,232847

0.233226

0.233604

0,233984

0.234363

0.234744

0.235122

0,235502

0.235882

0,236262

0.236643

0,237022

0,2374oi

0,237783

0.238163

0,238543

0,238924

0,239306

0,239687

0.240068

Age

Number 

of 

years

1302

1304

1306

1308

1310

1312

1314

1316

1318

1320

1322

1324

1326

1328

1330

1332

1334

1336

1338

1340

1342

1344

1346

1348

1350

1352

1354

1356

1358

1360

1362

1364

1366

1368

1370

1372

1374

1376

1378

1380

1382

1384

1386

1388

1390

1392

1394

1396

1398

1400

Error

2.9

2,9

2.9

2.9

2.9

2,9

2.9

2.9

2.9

2.9

2.9

2.9

2.9

2.9

2.9

3.0

3.0

3.0

3.0

3.0

3.0

3.0

3.0

3.0

3.0

3,0

3.0

3.0

3.0

3,0

3.0

3.0

3.0

3.0

3.0

3.0

3.0

3,1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

N 207/N23 5

Ratio

2.545752

2,552653

2.559564

2.566495

2.573437

2.580388

2,587360

2.594338

2.601335

2.608345

2.615367

2.622403

2.629455

2.6365i6

2.643593

2.650684

2.657792

2.664906

2.672041

2.679188

2.686349

2,693522

2,7007i4

2.7079i5

2,715129

2.722362

2.729607

2.736863

2.744136

2.751424

2.758724

2.766041

2.773370

2.7807H

2.788072

2.795445

2.802831

2.810232

2.817649

2.825076

2.832521

2.839981

2.847454

2.854939

2,862445

2,869960

2,877491

2.885039

2.8926oo

2.900174

Age

Number 

of 

years

1302

1304

1306

1308

1310

1312

1314

1316

1318

1320

1322

1324

1326

1328

1330

1332

1334

1336

1338

1340

1342

1344

1346

1348

1350

1352

1354

1356

1358

1360

1362

1364

1366

1368

1370

1372

1374

1376

1378

1380

1382

1384

1386

1388

1390

1392

1394

1396

1398

1400

Error 

±

29,2

29.3

29.3

29.4

29.4

29.4

29,5

29.5

29.6

29,6

29.7

29.7

29.8

29,8

29,8

29,9

29.9

30.0

30.0

30.1

30.1

30.2

30.2

30,2

30.3

30.3

30.4

30.4

30.5

30.5

30.6

30.6

30.7

30.7

30.7

30.8

30.8

30.9

30.9

3X0

31.0

3X1

3X1

3X1

3X2

3X2

3X3

3X3

3X4

3X4

N 207/N206

Ratio

0,083454

0,083538

0,083623

0,083708

0.083793

0.083878

0,083963

0,084049

0.084134

0,0842i9

0, 084305

0.084391

0.084477

0.084562

0.084648

0,084735

0.084821

0.084907

0.084993

0.085080

0.085167

0,085254

0,085340

0.085428

0, 085515

0.085602

0.085690

0.085777

0,085864

0.085953

0.086040

0,086128

0.0862i7

0.086304

0.086393

0.086481

0.086570

0.086658

0,086747

0.086836

0.086925

0.0870i4

0.087104

0.087193

0.087282

0.087372

0.087462

0.087551

0.087641

0.087731

Age

Number 

of 

years

1302

1304

1306

1308

1310

1312

1314

1316

1318

1320

1322

1324

1326

1328

1330

1332

1334

1336

1338

1340

1342

1344

1346

1348

1350

1352

1354

1356

1358

1360

1362

1364

1366

1368

1370

1372

1374

1376

1378

1380

1382

1384

1386

1388

1390

1392

1394

1396

1398

1400

Error

78.4

78.5

78,5

78.5

78.6

78.6

78.6

78.7

78.7

78,8

78,8

78.9

78,9

78.9

78,9

79,0

79,0

79.1

79,1

79,1

79.2

79.2

79.3

79.3

79.3

79.4

79.4

79,4

79,5

79.5

79.6

79,6

79.6

79.7

79.7

79.7

79.8

79.8

79,9

79.9

79.9

80,0

80,0

80,1

80,1

80,1

80,2

80,2

80,2

80.3

N208/

Ratio

0,065616

0.065719

0.065825

0.065928

0.066032

0.066136

0.066239

0.066345

0.066449

0,066552

0,066657

0.066760

0.066865

0.066970

0,067073

0.067177

0.067283

0,067386

0.067490

0,067594

0.067698

0.067804

0,067907

0.0680ii

0.068116

0,068219

0.068325

0.068428

0,068533

0,068637

0.068740

0.068846

0,068951

0.069054

0.069159

0.069263

0,069368

0.069472

0.069576

0,069680

0.069786

0.069889

0.069994

0.070098

0.070203

0.070308

0.070412

0.070516

0.070621

0,070726

/N232

Age

Number 

of 

years

1302

1304

1306

1308

1310

1312

1314

1316

1318

1320

1322

1324

1326

1328

1330

1332

1334

1336

1338

1340

1342

1344

1346

1348

1350

1352

1354

1356

1358

1360

1362

1364

1366

1368

1370

1372

1374

1376

1378

1380

1382

1384

1386

1388

1390

1392

1394

1396

1398

1400

Error

64,2

64.3

64.4

64.5

64.6

64.7

64.8

64.9

65.0

65,1

65.2

65.3

65.4

65.5

65.6

65.7

65,8

65,9

66.0

66.1

66.2

66.3

66,4

66.5

66.5

66.6

66.7

66,8

66.9

67.0

67.1

67.2

67.3

67.4

67.5

67.6

67.7

67.8

67,9

68.0

68,1

68.2

68.3

68.4

68,5

68.6

68.7

68.8

68.9

69.0
30 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

1402-1500

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.240448

0.240831

0.2412H

0.241594

0.241975

0,242357

0.242738

0.243121

0.243503

0.243886

0.2442&8

0.244652

0.245034

0.2454i5

0.2458oo

0.246181

0.246566

0.246948

0.247332

0.247715

0.248099

0.248482

0.248866

0.249250

0.249634

0.2500i9

0.2504oi

0.250787

0.251172

0.251557

0.251941

0.252325

0.2527H

0,253095

0.253480

0,253866

0.254251

0.254638

0.255022

0.255409

0,255796

0,256181

0,256569

Age

Number 

of 

years

1402

1404

1406

1408

1410

1412

1414

1416

1418

1420

1422

1424

1426

1428

1430

1432

1434

1436

1438

1440

1442

1444

1446

1448

1450

1452

1454

1456

1458

1460

1462

1464

1466

1468

1470

1472

1474

1476

1478

1480

1482

1484

1486

0,256954 1488

0.257340 1490

0.257728 1492

0.258113

0.2585oo

1494

1496

0.258887 1498

0.259274 1500

Error 

±

3.1

3.1

3.1

3,1

3.1

3.1

3.1

3.1

3.1

3.1

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3.2

3,3

3.3

3.3

3.3

3.3

3.3

3,3

3.3

3.3

3.3

3.3

3,3

3.3

3.3

3.3

3.3

3.3

3.3

^207/^235

Ratio

2.907767

2.915372

2.922991

2.930630

2.938278

2.945941

2.953624

2,9613i5

2,969024

2.976750

2.984489

2.992244

3.0000i5

3.0078oo

3.015597

3.0234U

3.031245

3.039090

3.046949

3.054829

3.062719

3.070625

3.078552

3.086486

3.094438

3.1024io

3.110393

3.118389

3.1264io

3.134440

3,142484

3.150548

3.158626

3.166718

3.174830

3.182954

3.191094

3.199248

3.207423

3.2156H

3.223814

3.232037

3.240273

3.248523

3.256795

3.265079

3,273379

3.281698

3.290029

3.298375

Age

Number 

of 

years

1402

1404

1406

1408

1410

1412

1414

1416

1418

1420

1422

1424

1426

1428

1430

1432

1434

1436

1438

1440

1442

1444

1446

1448

1450

1452

1454

1456

1458

1460

1462

1464

1466

1468

1470

1472

1474

1476

1478

1480

1482

1484

1486

1488

1490

1492

1494

1496

1498

1500

Error

3X5

3X5

3X6

3X6

3X6

3X7

31.7

31.8

3X8

3X9

3X9

32.0

32.0

32.0

32.1

32.1

32.2

32.2

32.3

32.3

32,4

32.4

32.4

32.5

32.5

32.6

32.6

32.7

32.7

32.8

32.8

32.9

32.9

32.9

33.0

33.0

33.1

33.1

33.2

33.2

33.3

33.3

33.3

33.4

33.4

33.5

33.5

33.6

33.6

33.7

N 207/N206

Ratio

0.087822

0,0879ii

0.0880o2

0.088092

0.088183

0.088274

0.088365

0.088456

0.088547

0.088638

0.088729

0.088820

0.0889i2

0.0890o4

0.089095

0.089188

0.089279

0.089372

0.089464

0.089557

0.089649

0.089742

0.089835

0.089928

0.090021

0.0901x3

0.090208

0.0903oo

0.090394

0.090487

0.09058X

0.090675

0.090769

0.090864

0.090958

0.09105 2

0.091147

0.091241

0.091336

0.091430

0.091525

0.091621

0.091715

0.0918H

0.0919o7

0.0920o2

0.092098

0.092194

0.092290

Age

Number 

of 

years

1402

1404

1406

1408

1410

1412

1414

1416

1418

1420

1422

1424

1426

1428

1430

1432

1434

1436

1438

1440

1442

1444

1446

1448

1450

1452

1454

1456

1458

1460

1462

1464

1466

1468

1470

1472

1474

1476

1478

1480

1482

1484

1486

1488

1490

1492

1494

1496

1498

0.092386 1500

Error

80.3

80.4

80.4

80.4

80.5

80,5

80.6

80.6

80.6

80.7

80.7

80.7

80.8

80.8

80.8

80.9

80.9

8X0

8X0

8X1

8X1

8X1

8X2

8X2

8X2

8X3

81.3

8X3

8X4

8X4

8X5

8X5

8X6

8X6

8X6

8X7

8X7

8X7

8X8

8X8

8X8

8X9

8X9

82.0

82.0

82.0

82.1

82.1

82.2

82.2

N208/

Ratio

0.070830

0.070934

0.071039

0.071144

0.071248

0.071353

0.071458

0.071562

0.071667

0.071771

0.071876

0.071980

0.072085

0.072190

0.072295

0.072399

0.072504

0.072609

0.072714

0.072819

0.072924

0.073029

0.073134

0.073237

0.073343

0.073448

0.073552

0.073657

0.073762

0.073867

0,073972

0.074076

0.074182

0.074287

0.074391

0.074496

0.0746oi

0.074706

0.0748H

0,0749i5

0.075021

0.075126

0.075230

0.075335

0.075440

0.075546

0.075651

0.075755

0.075861

0.075966

/N232

Age

Number 

of 

yearr

1402

140/1

1406

14 OP

1410

1412

1414

1416

141P

1420

1422

142/1

1426

142P

1430

1432

1431

1436

143P

1440

1442

144/1

1446

1448

1450

1452

145^

1456

145P

1460

1462

1461

1466

1468

1470

1472

1474

1476

147P

1480

1482

1484

1486

1488

1490

1492

1491

1496

149P

1500

Error

69.1

69.2

69,3

69.4

69.5

69.6

69,7

69.8

69.9

70.0

70.1

70,2

70,3

70.4

70.5

70.6

70,7

70.8

70.9

7X0

7X1

7X2

71.3

7X4

7X5

7X6

7X7

7X8

7X9

72.0

72.1

72.2

72.3

72.4

72,5

72.6

72.7

72,8

72.9

73.0

73.1

73.2

73.3

73.4

73.5

73.5

73.6

73.7

73.8

73.9
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

1505-1750

31

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.260243

0.261211

0.262180

0.263151

0,264120

0.265094

0.266067

0.267039

0.2680i3

0.268989

0.269964

0.270941

0.271917

0.272895

0.273872

0.274852

0.275833

0.276814

0.277796

0.278777

0.279761

0.280745

0.281729

0.282714

0.283702

0.284688

0.285676

0.286663

0.287653

0.288642

0.289632

0.290624

0.291616

0.2926io

0.293602

0.294598

0.295592

0.296589

0.297584

0.298584

0,299581

0,300580

0,301581

0.302580

0.303581

0.304584

0,305588

0.306591

0.307595

0.308599

Age

Number 

of 

years

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

1560

1565

1570

1575

1580

1585

1590

1595

1600

1605

1610

1615

1620

1625

1630

1635

1640

1645

1650

1655

1660

1665

1670

1675

1680

1685

1690

1695

1700

1705

1710

1715

1720

1725

1730

1735

1740

1745

1750

Error 

±

3.3

3,3

3,4

3.4

3.4

3.4

3,4

3.4

3.4

3.4

3.4

3.5

3.5

3.5

3.5

3.5

3,5

3.5

3.5

3.5

3.6

3.6

3.6

3.6

3.6

3.6

3.6

3.6

3.6

3.7

3.7

3.7

3.7

3.7

3.7

3.7

3,7

3.7

3.8

3.8

3.8

3.8

3.8

3.8

3.8

3.8

3.8

3.9

3.9

3.9

"207/^235

Ratio

3.319322

3.340369

3.361520

3.382772

3.404125

3.425585

3.447149

3.468821

3.490599

3.512473

3.534463

3.556557

3.578761

3.601073

3.623489

3.6460i9

3.668656

3.691406

3.714269

3.737235

3.760320

3.7835i6

3.806823

3.830246

3.853778

3.877430

3.901198

3.925082

3.949079

3.973190

3.997424

4.021775

4.046244

4.070834

4.095538

4.120370

4.145318

4.170392

4.195587

4.220898

4.246342

4.271905

4.297593

4.323407

4.349342

4.375408

4.401602

4.427922

4.454374

4.480945

Age

Number 

of 

years

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

1560

1565

1570

1575

1580

1585

1590

1595

1600

1605

1610

1615

1620

1625

1630

1635

1640

1645

1650

1655

1660

1665

1670

1675

1680

1685

1690

1695

1700

1705

1710

1715

1720

1725

1730

1735

1740

1745

1750

Error 

i

33.8

33.9

34.0

34.1

34.2

34.3

34,4

34.6

34.7

34.8

34.9

35.0

35.1

35,2

35.3

35,5

35.6

35,7

35.8

35,9

36.0

36.1

36,2

36.4

36.5

36.6

36.7

36.8

36.9

37.0

37.1

37,3

37,4

37.5

37.6

37.7

37.8

37,9

38.0

38,1

38.3

38,4

38.5

38.6

38.7

38.8

38.9

39.0

39.2

39.3

N 207/

Ratio

0.092626

0.092868

0.093111

0.093354

0.093598

0.093842

0.094088

0.094335

0.094582

0.094829

0.095078

0.095328

0.095578

0.095830

0.096082

0.096335

0.096588

0.096843

0.097098

0.097355

0.097612

0.097870

0.098128

0.098388

0.098648

0.0989io

0.099172

0.099435

0.099699

0.099964

0.100230

0.100496

0.100764

0.101032

0.101301

0.101571

0.101843

0.1021i4

0.102388

0.102660

0.102935

0.103211

0.103487

0.103765

0.104043

0,104322

0.104602

0.104883

0,105165

0,105448

'"206

Age

Number 

of 

years

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

1560

1565

1570

1575

1580

1585

1590

1595

1600

1605

1610

1615

1620

1625

1630

1635

1640

1645

1650

1655

1660

1665

1670

1675

1680

1685

1690

1695

1700

1705

1710

1715

1720

1725

1730

1735

1740

1745

1750

Error 

+

82.3

82,4

82.5

82.6

82.7

82.8

82,9

83,0

83,1

83.2

83.3

83.4

83.5

83,6

83.7

83.8

83.9

84.0

84.1

84,2

84.3

84.3

84.4

84,5

84.6

84.7

84.8

84.9

85.0

85.1

85.2

85.3

85.4

85.5

85.6

85.7

85.8

85,9

86.0

B6.1

86.2

86.3

86.4

86.5

86.6

86.7

86.8

86.9

87.0

87.1

^208/^232

Ratio

0,076229

0,076491

0,076754

0.0770i7

0.077279

0.077542

0,077806

0.078068

0.078331

0.078595

0.078857

0.079121

0,079384

0.079649

0.079912

0.080176

0,080439

0.080702

0.080966

0,081230

0.081494

0.081758

0.082022

0.082286

0,082550

0,0828i4

0.083078

0.083343

0.083608

0.083873

0.084137

0,0844oi

0,084666

0,084931

0.085196

0.085460

0.085725

0.085990

0.086255

0.086521

0.086786

0.087051

0,087317

0.087583

0.087849

0.0881i4

0.088380

0.088645

0.0889io

0.089176

Age

Number 

of 

years

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

1560

1565

1570

1575

1580

1585

1590

1595

1600

1605

1610

1615

1620

1625

1630

1635

1640

1645

1650

1655

1660

1665

1670

1675

1680

1685

1690

1695

1700

1705

1710

1715

1720

1725

1730

1735

1740

1745

1750

Error 

±

74.2

74.4

74,7

74.9

75.2

75,4

75.7

75.9

76.2

76,4

76.7

76.9

77.1

77.4

77.6

77.9

78.1

78.4

78.6

78.9

79.1

79.4

79.6

79.9

80.1

80.4

80,6

80.8

811

813

81.6

83,8

82,1

82.3

82.6

82.8

83.1

83.3

83,6

83.8

84.0

84.3

84.5

84.8

85,0

85.3

85,5

85,8

86.0

86.3
32 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

1755-2000

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0,3096o6

0,3106i4

0.311621

0.312630

0,313637

0.314648

0.315658

0.316671

0.317682

0.318696

0.319708

0.320723

0.321739

0.322756

0.323771

0.324789

0,325807

0.326827

0.327848

0.3288&7

0.329890

0.3309ii

0.331935

0.332959

0,333984

0.3350o9

0.336035

0.337062

0,33808 9

0.3391i9

0.340147

0.341179

0.342209

0.343241

0.344274

0.345308

0,346341

0.347377

0.3484ii

0.349450

0.350488

0.351525

0.3525&4

0.353604

0.354645

0,355685

0,356728

0.357771

0.3588i6

0.359859

Age

Number 

of 

years

1755

1760

1765

1770

1775

1780

1785

1790

1795

1800

1805

1810

1815

1820

1825

1830

1835

1840

1845

1850

1855

1860

1865

1870

1875

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

Error 

±

3.9

3.9

3.9

3.9

3.9

3.9

4.0

4.0

4.0

4.0

4.0

4.0

4.0

4.0

4.0

4.1

4.1

4.1

4.1

4.1

4.1

4.1

4.1

4.1

4.2

4.2

4.2

4.2

4,2

4.2

4.2

4.2

4.2

4.3

4.3

4.3

4.3

4.3

4,3

4.3

4,3

4.3

4.4

4.4

4.4

4.4

4.4

4.4

4.4

4.4

^207/^235

Ratio

4.507653

4.534493

4.5614&2

4.588554

4.615787

4,643153

4.670650

4.698282

4.726043

4.753945

4.781984

4,810156

4.838468

4.8669i3

4.895498

4.924230

4.953097

4.982106

5.011250

5.040542

5.069976

5.099554

5.129275

5.159136

5,189152

5,219307

5.249613

5.280068

5.3106&4

5.3414i4

5.372315

5,403365

5.434568

5,4659i5

5.497425

5.529084

5.560898

5.592872

5.624987

5.657274

5.6897io

5.7223io

5.7550&6

5.787976

5.821053

5.854291

5.887691

5.921252

5.954970

5,988862

Age

Number 

of 

years

1755

1760

1765

1770

1775

1780

1785

1790

1795

1800

1805

1810

1815

1820

1825

1830

1835

1840

1845

1850

1855

1860

1865

1870

1875

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

Error 

+

39.4

39,5

39.6

39.7

39.8

39.9

40.1

40.2

40.3

40.4

40.5

40.6

40.7

40.8

41.0

41.1

41.2

41.3

41.4

41.5

41.6

41.7

43,9

42.0

42.1

42.2

42.3

42.4

42.5

42.6

42.7

42.9

43.0

43.1

43.2

43.3

43.4

43.5

43.6

43.8

43.9

44.0

44,1

44.2

44.3

44.4

44.5

44.7

44.8

44.9

N 207/N2Q6

Ratio

0.105732

0.1060i6

0.106302

0.106588

0,106877

0.107165

0.107454

0.107744

0.108036

0.108328

0.108622

0.1089i6

0.109211

0.109507

0.109805

0.110103

0,110403

0.110703

0.111004

0.111307

0.111609

0.1119i4

0.1122i9

0.112525

0.112833

0,113141

0.113451

0,113761

0.114073

0.114385

0.114699

0,1150i3

0,115329

0,115645

0,115963

0.116282

0.116602

0.116922

0,117245

0.117567

0.117891

0.1182i7

0,118543

0.118870

0.119199

0.119529

0.119859

0.120191

0.120524

0.120858

Age

Number 

of 

years

1755

1760

1765

1770

1775

1780

1785

1790

1795

1800

1805

1810

1815

1820

1825

1830

1835

1840

1845

1850

1855

1860

1865

1870

1875

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

Error 

±

87.2

87.3

87,4

87.5

87.6

87.7

87.8

87.9

88.0

88.1

88.2

88.3

88.4

88.5

88,6

88.7

88.8

88.9

89.0

89.1

89.2

89.3

89.4

89.5

89.6

89.7

89.8

89.9

90.0

90.1

90.2

90.3

90,4

90.5

90.6

90.7

90.8

90.9

91.0

91.1

91.2

91,3

91.4

91.5

91.6

93,7

91,8

9X9

92.0

92.1

^208/^232

Ratio

0,089442

0,089708

0.089974

0.090240

0,090506

0.090772

0,091038

0.091305

0.091572

0,091839

0.092104

0.092371

0,092637

0,092904

0.093170

0.093437

0.093704

0.093971

0.094238

0,094505

0.094772

0.095039

0.095306

0.095575

0.095842

0.096109

0.096377

0.096644

0.0969i3

0.097180

0,097448

0.097717

0,097984

0.098252

0.098520

0,098788

0,099056

0.099324

0.099593

0.0998&2

0.100130

0.100398

0.1006&8

0.100936

0.101205

0.101473

0.101742

O.l020io

0,102279

0,102549

Age

Nuirber 

of 

years

1755

1760

1765

1770

1775

1780

1785

1790

1795

1£00

1805

1£10

IE 15

1820

1£25

1£30

1£35

U40

1£45

If50

If55

1£60

lf<>5

If70

1£75

IfBO

1PB5

If90

1P95

1°00

1905

1910

1915

1920

1°25

1°30

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

Error 

±

86,5

86.8

87.0

87.3

87.5

87.7

sao

88,2

88.5

88.7

89.0

89.2

89.5

89.7

90.0

90.2

90.5

90.7

910

93,2

91.4

91.7

91.9

92.2

92.4

92.7

92.9

93.2

93.4

93.7

93.9

94.2

94.4

94,6

94.9

95.1

95.4

95.6

95.9

96.1

96.4

96.6

96.9

97.1

97.4

97,6

97.9

98.1

98.3

98.6
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

2005-2250

33

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.360905

0.361951

0.362998

0.36404?

0.365094

0.366144

0.367194

0.368245

0.369296

0.370349

0.371403

0.372458

0.3735ii

0.374569

0,375624

0,376682

0.377742

0.378799

0.379859

0.380921

0.381982

0,383043

0.3841o9

0.385172

0.386236

0.387303

0.388368

0.389436

0.390504

0.3915 73

0.392643

0.3937i4

0.394783

0.395857

0.39693 o

0.3980o5

0.399078

0,400154

0.401231

0.402307

0.403387

0.404464

0.405546

0.406625

0.407706

0.408788

0.409873

0.410956

0.412041

0,413125

Age

Number 

of 

years

2005

2010

2015

2020

2025

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095

2100

2105

2110

2115

2120

2125

2130

2135

2140

2145

2150

2155

2160

2165

2170

2175

2180

2185

2190

2195

2200

2205

2210

2215

2220

2225

2230

2235

2240

2245

2250

Error 

+

4.4

4.5

4.5

4.5

4.5

4.5

4.5

4.5

4.5

4.5

4.6

4,6

4.6

4.6

4.6

4.6

4.6

4.6

4.6

4.7

4.7

4.7

4.7

4.7

4.7

4.7

4.7

4.7

4.8

4.8

4.8

4.8

4.8

4.8

4.8

4.8

4.8

4.9

4.9

4.9

4.9

4.9

4.9

4.9

4.9

4.9

5.0

5.0

5.0

5.0

L N 207/N235

Ratio

6, 0229i8

6.057140

6.091526

6.126076

6.160799

6.195695

6.230758

6.265992

6.301391

6.336972

6.372720

6.408648

6.444749

6.4810i9

6.517473

6,5541o4

6.5909i2

6.627904

6,665064

6.7024i4

6.739946

6.777662

6.815561

6.853638

6.891908

6.930364

6.969005

7.007839

7.046852

7.086061

7.125465

7,165058

7.204844

7.2448i9

7.284996

7.325365

7.36593 3

7.406698

7.447655

7.4888i9

7.530185

7.571751

7,613518

7.655485

7.697660

7.740041

7.782628

7.825426

7.868422

7.911637

Age

Number 

of

years

2005

2010

2015

2020

2025

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095

2100

2105

2110

2115

2120

2125

2130

2135

2140

2145

2150

2155

2160

2165

2170

2175

2180

2185

2190

2195

2200

2205

2210

2215

2220

2225

2230

2235

2240

2245

2250

Error

±

45.0

45.1

45.2

45.3

45.4

45.6

45.7

45.8

45.9

46.0

46.1

46.2

46.3

46.5

46.6

46.7

46.8

46.9

47.0

47.1

47.2

47.3

47.5

47.6

47.7

47.8

47.9

48.0

48.1

48.2

48.4

48,5

48.6

48.7

48.8

48.9

49.0

49.1

49.3

49.4

49,5

49.6

49.7

49.8

49.9

50.0

50.2

50.3

50.4

50.5

N 207/N206

Ratio

0.121193

0.121530

0,121867

0.122205

0.122545

0.122886

0.123228

0.123571

0.1239i6

0.124261

0.124607

0.124955

0.125305

0.125654

0.1260o6

0.126358

0.1267H

0.127067

0.127423

0.127779

0.128138

0.128498

0,128858

0,129220

0.129584

0.129948

0.130314

0.130681

0.131049

0.131419

0.131789

0,132161

0.132535

0.132909

0.133285

0,133661

0.134040

0.1344i9

0.1348oo

0.135182

0.135565

0.135951

0.136336

0.136723

0,137112

0,137502

0.137893

0.138286

0,138679

0.139075

Age

Number 

of 

years

2005

2010

2015

2020

2025

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095

2100

2105

2110

2115

2120

2125

2130

2135

2140

2145

2150

2155

2160

2165

2170

2175

2180

2185

2190

2195

2200

2205

2210

2215

2220

2225

2230

2235

2240

2245

2250

Error 

+

92.2

92.3

92.4

92.5

92.6

92.7

92.8

92.9

93.0

93.1

93.2

93.3

93.4

93.5

93.6

93.7

93.8

93.9

94.0

94.1

94.2

94.3

94.4

94.5

94.6

94,7

94.8

94.9

95.0

95.1

95.2

95.3

95.5

95.6

95.7

95,8

95.9

96,0

96.1

96,2

96.3

96.4

96.5

96.6

96.7

96.8

96.9

97.0

97,1

97.2

N208/N 232

Ratio

0.102818

0,103087

0.103356

0.103626

0,103895

0.104166

0,104435

0.104704

0.104974

0.105243

0.1055i4

0.105783

0.106053

0.106322

0.106593

0,106863

0.107133

0,107402

0.107674

0.107944

0.108214

0.108486

0,108756

0.109026

0.109296

0.109568

0.109838

0.110108

0,110380

0.110652

0,110922

0.111194

0,111465

0,111738

0.112008

0,112279

0.112551

0,112822

0.113095

0.113366

0.113637

0,1139o9

0.114181

0,114453

0,114724

0.114996

0.115269

0,115540

0.115814

0.116087

Age

Number 

of

years

2005

2010

2015

2020

2025

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095

2100

2105

2110

2115

2120

2125

2130

2135

2140

2145

2150

2155

2160

2165

2170

2175

2180

2185

2190

2195

2200

2205

2210

2215

2220

2225

2230

2235

2240

2245

2250

Error 

+

98,8

99,1

99,3

99.6

99.8

100,1

100.3

1006

1008

101,1

101.3

101.5

101,8

102.0

102.3

102.5

102.8

103.0

103.3

103.5

103.8

104.0

104.3

104.5

104.8

105.0

105.2

105.5

105.7

106.0

106.2

106.5

106.7

107.0

107.2

107.5

107.7

108,0

108.2

108.5

108.7

108,9

109.2

109.4

109.7

:.09.9

110,2

110.4

110.7

110.9
34 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

2255-2500

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

"206/^238

Ratio

0.4142ii

0.4153oo

0,416386

0.417477

0.4185&5

0.419658

0.420747

0.421840

0.422932

0.424026

0.425121

0.4262i7

0.4273i3

0.428409

0.4295o9

0.430608

0,431707

0.432807

0.4339io

0, 4350i2

0,4361i6

0,4372i9

0,438325

0.439430

0.440537

0.441643

0.442752

0.4438&2

0.444971

0.446082

0.447193

0.448307

0.4494i9

0.450535

0.451648

0.452765

0.453882

0.454998

0,4561i7

0,457236

0.458357

0.459479

0,4606o2

0.461723

0,462849

0.463972

0.465097

0.466224

0.467352

0,468478

Age

Number 

of 

years

2255

2260

2265

2270

2275

2280

2285

2290

2295

2300

2305

2310

2315

2320

2325

2330

2335

2340

2345

2350

2355

2360

2365

2370

2375

2380

2385

2390

2395

2400

2405

2410

2415

2420

2425

2430

2435

2440

2445

2450

2455

2460

2465

2470

2475

2480

2485

2490

2495

2500

Error 

+

5.0

5.0

5.0

5.0

5.0

5.1

5.1

5.1

5.1

5.1

5.1

5.1

5.1

5.1

5,2

5.2

5.2

5.2

5.2

5.2

5,2

5.2

5.2

5.3

. 5,3

5.3

5.3

5.3

5.3

5.3

5.3

5.3

5.4

5.4

5.4

5.4

5.4

5.4

5.4

5.4

5.4

5.5

5.5

5.5

5.5

5.5

5.5

5.5

5.5

5.5

. N 207

Ratio

7.95506

7.99870

8.04254

8.08660

8,13088

8.17537

8.220o8

8.265oi

8.310i4

8.35551

8.401io

8.44691

8,49294

8.539i9

8.58567

8.63238

8.67932

8.72649

8.77387

8.82150

8.86936

8.91745

8.96577

9.01433

9.063i2

9.112i6

9.16143

9.21095

9.26070

9.310&9

9.36093

9.41142

9.462i6

9.513i3

9.56436

9.61584

9.66756

9.71955

9.77177

9.82426

9.877oo

9.930oo

9.98327

10.03677

10,09055

10.14460

10.19890

10.25347

10.30830

10.36340

7^235

Age

Number 

of 

years

2255

2260

2265

2270

2275

2280

2285

2290

2295

2300

2305

2310

2315

2320

2325

2330

2335

2340

2345

2350

2355

2360

2365

2370

2375

2380

2385

2390

2395

2400

2405

2410

2415

2420

2425

2430

2435

2440

2445

2450

2455

2460

.2465

2470

2475

2480

2485

2490

2495

2500

Error 

+

50.6

50.7

50,8

50,9

5X1

5X2

5X3

5X4

5X5

51.6

5X7

5X8

5X9

52.1

52.2

52.3

52,4

52.5

52.6

52.7

52.8

53,0

53.1

53.2

53.3

53.4

53.5

53.6

53.7

53.9

54.0

54.1

54.2

54.3

54.4

54.5

54.6

54,8

54.9

55.0

55.1

55.2

55.3

55.4

55.5

55.7

55.8

55.9

56.0

56.1

N 207/

Ratio

0.139472

0.139869

0.1402&9

0,140669

0.141071

0.141474

0.141879

0.142285

0.142693

0,1431o2

0.1435i2

0,143923

0.144337

0.144751

0.145167

0.145584

0.146003

0.146423

0.146844

0.1472&7

0.147691

0.1481i8

0.148544

0.148973

0.149403

0.149835

0,150268

0.150703

0.151139

0.151577

0,1520i6

0.152456

0,152899

0.153341

0.153787

0.154234

0.154682

0,155132

0.155583

0,156036

0.156490

0.156945

0.157403

0.1578&2

0.158322

0.158784

0.159248

0.1597i3

0,160180

0,160649

^206

Age

Number 

of 

years

2255

2260

2265

2270

2275

2280

2285

2290

2295

2300

2305

2310

2315

2320

2325

2330

2335

2340

2345

2350

2355

2360

2365

2370

2375

2380

2385

2390

2395

2400

2405

2410

2415

2420

2425

2430

2435

2440

2445

2450

2455

2460

2465

2470

2475

2480

2485

2490

2495

2500

Error 

±

97.3

97.4

97.5

97.6

97.7

97.8

97.9

98.0

98.1

98.2

98,3

98.4

98.5

98.6

98.7

98.8

98,9

99,0

99,1

99.3

99,3

99,5

99.6

99.7

99.8

99.9

100,0

100.1

100.2

100.3

100.4

100.5

100.6

100.7

100.8

100.9

10X0

101,1

10X2

10X3

10X4

10X5

10X6

10X8

10X9

102,0

102.1

102.2

102.3

102.4

N208/W 232

Ratio

0.116360

0.116632

0.116904

0.117176

0.117450

0.117722

0.117995

0.1182&7

0,118540

0.118813

0.119086

0.119359

0.119632

0.119907

0.120180

0.120453

0.120727

0.12lOoi

0,121274

0.121548

0,121822

0.122095

0.122369

0,122643

0, 122916

0.123191

0.123464

0.123739

0.1240i4

0.124288

0.124562

0,124837

0.125113

0.125387

0.125661

0.125936

0.1262io

0.126485

0.1267&0

0.127036

0.1273io

0.127585

0.1278&0

0.128137

0,1284ii

0.128687

0.1289&3

0.1292*9

0.129515

0.129790

Age

Number 

of 

years

2255

2260

2265

2270

2275

2280

2285

2290

2295

2300

2305

2310

2315

2320

2325

2330

2335

2340

2345

2350

2355

2360

2365

2370

2375

2380

2385

2390

2395

2400

2405

2410

2415

2420

2425

2430

2435

2440

2445

2450

2455

2460

2465

2470

2475

2480

2485

2490

2495

2500

Error 

+

111.2

11X4

11X7

11X9

112,1

112.4

112.6

112.9

113.1

113,4

113.6

113.9

114.1

114.4

114,6

114.9

115.1

115.4

115.6

115.8

nea

116.3

116.6

116.8

117.1

117.3

117.6

117.8

118.1

118.3

118.6

118.8

119.0

119.3

119.5

119.8

120.0

120.3

120.5

120.8

12X0

12X3

12X5

12X8

122.0

122.3

122.5

122.7

123.0

123.2
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

2510-3000

35

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.470737

0.472999

0.475266

0.477535

0,4798o6

0.482083

0.484363

0.486644

0.488933

0.491222

0.4935i5

0.4958i3

0.4981i3

0.5004i8

0.502726

0.505037

0.507352

0.509671

0.511992

0.5143i8

0.516647

0.518981

0.5213i6

0.523656

0.5260oo

0.528349

0.530698

0.533052

0.5354io

0.537771

0.540137

0.542506

0.544878

0.547254

0.549634

0.5520i7

0.554406

0.556796

0.559190

0.561588

0.563993

0.566397

0,568805

0.571216

0.573635

0.576055

0.578479

0.580907

0.583339

0.585775

Age

Number 

of 

years

2510

2520

2530

2540

2550

2560

2570

2580

2590

2600

2610

2620

2630

2640

2650

2660

2670

2680

2690

2700

2710

2720

2730

2740

2750

2760

2770

2780

2790

2800

2810

2820

2830

2840

2850

2860

2870

2880

2890

2900

2910

2920

2930

2940

2950

2960

2970

2980

2990

3000

Error 

±

5.6

5.6

5.6

5.6

5.7

5.7

5.7

5.7

5.7

5^8

5.8

5^8

5.8

5.9

5.9

5.9

5.9

5.9

6,0

6.0

6.0

6.0

6.1

6.1

6.1

6.1

6.1

6.2

6,2

6.2

6,2

6.3

6.3

6.3

6.3

6.3

6.4

6,4

6.4

6,4

6.5

6,5

6.5

6,5

6.5

6,6

6.6

6.6

6.6

6.7

^207

Ratio

10.47442

10.58650

10.69970

10.81399

10.92940

11.04594

11.16361

11.28244

1X40243

11,52358

11.64593

11.76947

1X89421

12.020i9

12.14737

12,27581

12.40550

12.53646

12.66870

12.80222

12.93706

13.07321

13.21069

13.34953

13.48970

13.63125

13.77417

13.91851

14.06426

14.21141

14.360o2

14.510o6

14.66159

14.81459

14.96908

15.12508

15.28260

15.44167

15.60229

15.76447

15.92826

16.09361

16.26061

16.42923

16.59949

16.77143

16.94502

17.12034

17.29737

17.476io

/^235

Age

Number 

of 

years

2510

2520

2530

2540

2550

2560

2570

2580

2590

2600

2610

2620

2630

2640

2650

2660

2670

2680

2690

2700

2710

2720

2730

2740

2750

2760

2770

2780

2790

2800

2810

2820

2830

2840

2850

2860

2870

2880

2890

2900

2910

2920

2930

2940

2950

2960

2970

2980

2990

3000

Error 

±

56,3

56.5

56.8

57.0

57.2

57.4

57.7

57.9

58.1

58.3

58.6

58.8

59.0

59.2

59.5

59.7

59.9

60.1

60.4

60.6

60.8

6X0

6X3

6X5

6X7

6X9

62.2

62.4

62.6

62.8

63.1

63.3

63.5

63.7

64.0

64.2

64.4

64.6

64.9

65,1

65.3

65.5

65.8

66.0

66.2

66.4

66.6

66.9

67.1

67,3

N 207/N206

Ratio

0.161591

0.162539

0.163493

0.164455

0.165423

0.166397

0.167378

0.168367

0.169361

0.170363

0.171372

0.172387

0.173409

0.174439

0.175475

0.1765i9

0.177570

0.178628

0.179694

0.180767

0.181847

0.182935

0.184030

0.185133

0.186244

0.187361

0.188488

0.189622

0.190764

0.191913

0.193071

0.194236

0.1954io

0.196592

0.197782

0.198980

0.200186

0.201402

0.202626

0.203858

0.205097

0.206347

0.207605

0.208873

0.210148

0.211432

0.212726

0,214028

0,215340

0,216660

Age

Number 

of 

years

2510

2520

2530

2540

2550

2560

2570

2580

2590

2600

2610

2620

2630

2640

2650

2660

2670

2680

2690

2700

2710

2720

2730

2740

2750

2760

2770

2780

2790

2800

2810

2820

2830

2840

2850

2860

2870

2880

2890

2900

2910

2920

2930

2940

2950

2960

2970

2980

2990

3000

Error 

±

102,6

102.8

103.0

103.2

103.4

103.6

103.8

104.1

104.3

104.5

104.7

104,9

105,1

105.3

105.5

105.7

106,0

106.2

106.4

106.6

106.8

107.0

107.2

107.4

107.7

107.9

108.1

108.3

108.5

108.7

108.9

109,1

109,4

109.6

109.8

110.0

110.2

110,4

110.6

110.9

11X1

11X3

11X5

11X7

11X9

112.1

112.4

112.6

112.8

113.0

N208/N 232

Ratio

0.130341

0.130893

0.131444

0.131997

0.132550

0.133104

0.133657

0.1342io

0.134763

0.135317

0.135871

0.136428

0.136982

0,137537

0,138092

0.138647

0.139203

0.139760

0.140316

0.140874

0.141430

0.141988

0.142546

0.143103

0,143661

0.144219

0.144778

0.145338

0.145896

0.146456

0.1470i6

0.147575

0,148136

0,148695

0.149257

0.1498i8

0.150381

0.150942

0.151503

0.152065

0.152627

0.153192

0.153754

0.154317

0.154880

0.155445

0.156008

0.156572

0.157138

0.157704

Age

Number 

of 

years

251C

252C

253C

254C

255C

256C

257C

258C

259C

2600

2610

2620

2630

2640

2650

2660

2670

2680

2690

2700

2710

2720

2730

2740

2750

2760

2770

2780

2790

2800

2810

2820

2830

2840

2850

2860

2870

2880

2890

2900

2910

2920

2930

2940

2950

2960

2970

2980

2990

3000

Error 

+

123,7

124.2

124.7

125.2

125.7

126,2

126,7

127,2

127.7

128.2

128.7

129.2

129.6

130.1

130,6

13X1

13X6

132.1

132,6

133.1

133.6

134.1

134.6

135.1

135.6

136.1

136.5

137.0

137,5

138.0

138.5

139.0

139.5

140.0

140.5

14X0

14X5

142.0

142.5

143,0

143.5

143.9

144.4

144.9

145.4

145.9

146,4

146.9

147.4

147,9
36 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

3010-3500

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.5882i3

0.590656

0.593103

0.595553

0.5980o6

0.6004&4

0.602928

0.605393

0.6078&2

0.610335

0.6128ii

0.615292

0.617777

0.6202&6

0.622757

0.625255

0.627752

0.630256

0.6327&5

0.635275

0,637791

0.6403io

0.642833

0.645360

0.647891

0.650425

0.6529&5

0.655506

0.658052

0.6606oo

0.663155

0.665714

0.668276

0.670843

0.673412

0.675985

0.678564

0.681148

0.683733

0.686323

0.6889i6

0.691513

0.6941i4

0.696721

0.699330

0.701944

0.704561

0.707183

0.709808

0.712439

Age

Number 

of 

years

3010

3020

3030

3040

3050

3060

3070

3080

3090

3100

3110

3120

3130

3140

3150

3160

3170

3180

3190

3200

3210

3220

3230

3240

3250

3260

3270

3280

3290

3300

3310

3320

3330

3340

3350

3360

3370

3380

3390

3400

3410

3420

3430

3440

3450

3460

3470

3480

3490

3500

Error 

±

6,7

6.7

6.7

6,7

6.8

6.8

6.8

6.8

6.9

6.9

6.9

6.9

6.9

7.0

7.0

7,0

7.0

7.1

7.1

7.1

7.1

7.1

7.2

7.2

7,2

7.2

7.3

7.3

7.3

7.3

7.3

7.4

7.4

7.4

7.4

7.5

7.5

7.5

7.5

7.5

7.6

7.6

7.6

7.6

7,6

7.7

7.7

7.7

7.7

7.8

N 207/N235

Ratio

17.65661

17.83885

18.02289

1820874

18.39637

18.58586

18.77718

18,9704 o

19.16550

19.36248

19.56141

19.76227

19.965io

20.16992

20.37671

20.58555

20.79641

21.00935

21.22437

2X44146

2X66070

2X882o6

22.10561

22.33133

22.55924

22.78940

23.02179

23.25646

23.49344

23.73270

23.97432

24.21829

24.46465

24.71342

24.964&0

25.21826

25.47438

25.733oi

25.994i8

26.25787

26.52416

26.79303

27.06455

27.33873

27.61555

27.895H

28.17737

28.46241

28.75024

29.04086

Age

Number 

of 

years

3010

3020

3030

3040

3050

3060

3070

3080

3090

3100

3110

3120

3130

3140

3150

3160

3170

3180

3190

3200

3210

3220

3230

3240

3250

3260

3270

3280

3290

3300

3310

3320

3330

3340

3350

3360

3370

3380

3390

3400

3410

3420

3430

3440

3450

3460

3470

3480

3490

3500

Error 

±

67.5

67.8

68.0

68.2

68.4

68.7

68.9

69.1

69,3

69.6

69.8

70.0

70.2

70.5

70.7

70.9

7X1

71.4

7X6

7X8

72.0

72.3

72.5

72.7

72.9

73.2

73.4

73.6

73.8

74.1

74.3

74.5

74.7

75,0

75.2

75.4

75.6

75.8

76.1

76.3

76.5

76.7

77.0

77.2

77.4

77.6

77,9

78.1

78.3

78.5

^2077

Ratio

0.217991

0.219330

0.220678

0.22203 7

0.223404

0.224782

0.2261&8

0.227564

0.228971

0.230387

0.2318i4

0.233249

0.234696

0.236152

0.237619

0.239095

0.240583

0.242081

0.243589

0.245108

0.246638

0.248178

0.249729

0.251292

0.252865

0.254449

0.256044

0.257651

0.259270

0.2609oo

0.262541

0.264193

0.265857

0.267533

0.269221

0,270921

0,272633

0,274356

0.276093

0.277841

0.279602

0.281376

0.283162

0,284961

0.286772

0.288596

0.290434

0.292284

0.294148

0,296024

//V206

Age

Number 

of 

years

3010

3020

3030

3040

3050

3060

3070

3080

3090

3100

3110

3120

3130

3140

3150

3160

3170

3180

3190

3200

3210

3220

3230

3240

3250

3260

3270

3280

3290

3300

3310

3320

3330

3340

3350

3360

3370

3380

3390

3400

3410

3420

3430

3440

3450

3460

3470

3480

3490

3500

Error 

±

113.2

113,4

113.7

113.9

114.1

114.3

114.5

114.7

115.0

115.2

115.4

115.6

115.8

116.0

116.3

116.5

116.7

116.9

117.1

117,3

117.6

117,8

118.0

118.2

1184

118,7

118.9

119.1

119.3

119,5

119.8

120,0

120.2

120.4

120.6

120.9

121.1

12X3

12X5

12X7

12X9

122.2

122.4

122.6

122.8

123.1

123.3

123.5

123,7

123.9

N 208/N 232

Ratio

0.158268

0,158833

0.159399

0.1599&6

0.160531

0.161098

0.1616&5

0.162233

0.1628oo

0.163368

0.163936

0.164504

0.16507 2

0.165642

0.1662ii

0,166780

0.167349

0.167920

0.168490

0.169060

0.169631

0.170203

0.170774

0.171346

0,1719i7

0.172489

0.173062

0.173635

0.174208

0.174782

0.175354

0.175928

0.176502

0.177077

0.177651

0.178226

0.178802

0.179377

0.179955

0.180530

0.181106

0.181683

0.182260

0.182839

0.183415

0.183992

0.184571

0.185148

0,185727

0.186307

Age

Number 

of

year?

301C

302C

303G

304C

305C

306C

307C

308C

309C

310C

311C

312 C

313C

314C

315C

316C

317C

318C

319C

320C

3210

3220

3230

3240

3250

3260

3270

3280

3290

3300

3310

3320

3330

3340

3350

3360

3370

3380

3390

3400

3410

3420

3430

3440

3450

3460

3470

3480

3490

3500

Error 

±

148.4

148.9

149.4

149.9

150.4

150.8

151.3

15X8

152.3

152.8

153.3

153.8

154.3

154.8

155.3

155.8

156.3

156,8

157.3

157.7

158.2

158.7

159,2

159.7

160.2

160.7

161.2

16X7

162.2

162.7

163.2

163.7

164.2

164.6

165.1

165.6

166.1

166.6

167.1

167.6

168.1

168.6

169.1

169,6

170.1

170.6

171,1

17X5

172.0

172,5
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

3510-4000

37

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Ratio

0.715073

0.717712

0,720353

0.722997

0.725648

0.728304

0.730961

0.733623

0.736292

0.7389&1

0.741637

0.744316

0.746998

0.749686

0.752377

0.755070

0.757770

0.760474

0,763182

0.765894

0.7686io

0.771329

0,774056

0.776784

0.779517

0.782254

0.784996

0.787740

0.790489

0.793244

0.7960oi

0.798764

0.801530

0.804301

0.807077

0.809857

0.812641

0.815430

0,818222

0.8210i8

0.823817

0.826623

0.829432

0.832247

0.835065

0.837887

0.840715

0.843546

0.846382

0.849221

Age

Number 

of 

years

3510

3520

3530

3540

3550

3560

3570

3580

3590

3600

3610

3620

3630

3640

3650

3660

3670

3680

3690

3700

3710

3720

3730

3740

3750

3760

3770

3780

3790

3800

3810

3820

3830

3840

3850

3860

3870

3880

3890

3900

3910

3920

3930

3940

3950

3960

3970

3980

3990

4000

Error 

±

7.8

7.8

7.8

7.8

7.9

7.9

7.9

7.9

8.0

8.0

8.0

8.0

8.0

8.1

8.1

8.1

8.1

8.2

8.2

8,2

8.2

8.2

8.3

8.3

8.3

8,3

8.4

8.4

8.4

8.4

8.4

8.5

8.5

8.5

8.5

8.6

8,6

8,6

8.6

8.6

8.7

8.7

8,7

8.7

8.8

8.8

8.8

8.8

8.8

8,9

N 207/N235

Ratio

29.33434

29.630&5

29.92990

30.23203

30.53715

30.84526

31.15633

31.47048

31.78766

32,10798

32.43143

32.758oo

33.08779

33.42078

33.75705

34.09660

34.43945

34.78567

35.13523

35.48826

35.84473

36,20464

36.568ii

36,93509

37.30569

37.67992

38.05776

38.43933

38.82459

39.21365

39.60652

40.00318

40.40375

40.80820

41,21664

41.62907

42.04549

42.46602

42.890&2

43.3194 o

43.75238

44.18953

44.631oi

45.07675

45.52689

45,98144

46.44037

46.90383

47.371 7 8

47.84434

Age

Number 

of 

years

3510

3520

3530

3540

3550

3560

3570

3580

3590

3600

3610

3620

3630

3640

3650

3660

3670

3680

3690

3700

3710

3720

3730

3740

3750

3760

3770

3780

3790

3800

3810

3820

3830

3840

3850

3860

3870

3880

3890

3900

3910

3920

3930

3940

3950

3960

3970

3Q80

3990

4000

Error 

±

78,8

79.0

79.2

79.4

79.7

79.9

80.1

80,3

80.6

80.8

8X0

81.2

81.5

8X7

81.9

82.1

82.4

82.6

 82.8

83.0

83.3

83.5

83.7

83.9

84.2

84.4

84.6

84.8

85.0

85.3

85.5

85.7

85.9

86.2

86.4

86.6

86.8

87.1

87.3

87.5

87.7

88.0

88.2

88,4

88.6

88.9

89.1

89.3

89.5

89.8

N 207/N206

Ratio

0.2979i4

0.299817

0.301735

0.303666

0.3056io

0.307568

0.309540

0.311527

0.313526

0.315542

0.317570

0.319614

0,321672

0.323745

0.325833

0.327936

0.330053

0.332186

0.334334

0.336497

0.338676

0.3408?!

0.343080

0.345306

0.347548

0.349806

0.352080

0.354371

0.356678

0.3590oi

0,361342

0.363698

0.366073

0.368463

0.370871

0.373296

0.375739

0.378199

0.380677

0.383173

0.385688

0.388220

0.390770

0.393338

0.395925

0,398532

0.401155

0,403799

0.406461

0.409143

Age

Number 

of 

years

3510

3520

3530

3540

3550

3560

3570

3580

3590

3600

3610

3620

3630

3640

3650

3660

3670

3680

3690

3700

3710

3720

3730

3740

3750

3760

3770

3780

3790

3800

3810

3820

3830

3840

3850

3860

3870

3880

3890

3900

3910

3920

3930

3940

Error 

+

124.2

124.4

124.6

124.8

125.0

125.3

125.5

125.7

125,9

126,2

126.4

126.6

126.8

127,0

127,3

127.5

127,7

127.9

128.2

128.4

128.6

128.8

129.0

129.3

129.5

129.7

129.9

130.2

130.4

130,6

130.8

13X1

13X3

13X5

131.7

132.0

132.2

132.4

132.6

132.9

133,1

133.3

133.5

133,8

3950 134.0

3960 134.2

3970 134.4

3980 134,7

3990 134.9

4000 135.1

N208/N232

Ratio

0.186885

0.187466

0.188045

0.188625

0.189206

0.189785

0.190366

0.190947

0.191530

0.192112

0.192694

0.193276

0,193859

0.194441

0.195023

- 0.195607

0.196192

0,196777

0.197359

0.197944

0.198529

0.1991i4

0.199699

0.200287

0.200872

0.201459

0.202044

0.202631

0.203218

0.203806

0.204393

0.204982

0.205571

0.206159

0.206748

0.207336

0.207927

0.208517

0.209108

0.209697

0.210288

0.210879

0.211470

0.212061

0,212653

0,213245

0.213838

0.214431

0.215023

0.215616

Age

Number 

of 

years

3510

3520

3530

3540

3550

3560

3570

3580

3590

3600

3610

3620

3630

3640

3650

3660

3670

3680

3690

3700

3710

3720

3730

3740

3750

3760

3770

3780

3790

3800

3810

3820

3830

3840

3850

3860

3870

3880

3890

3900

3910

Error 

±

173,0

173.5

174.0

174.5

175.0

175.5

176.0

176.5

177.0

177.5

178.0

178.5

178.9

179,4

179.9

180.4

180.9

181.4

18X9

182.4

182.9

183.4

183.9

184,4

184.9

185,4

185.8

186.3

186,8

187.3

187.8

188,3

188.8

189.3

189.8

190.3

190.8

19X3

191.8

192.3

192.7

3920 193.2

3930 193.7

3940 194.2

3950 194,7

3960 195,2

3970 195.7

3980 196,2

3990 196.7

4000 197.2
38 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

4010-4500

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

N 206/N 238

Age

Ratio Numfber Error

of +

years

0.85206? 4010 8.9 

0.8549i5 4020 8.9 

0.857765 4030 8,9 

0.860626 4040 9.0 

0.863486 4050 9.0

0.866352 4060 9.0 

0.869224 4070 9.0 

0.872099 4080 9.0 

0.874978 4090 9.1 

0.877861 4100 9.1

0.880750 4110 9.1 

0.883644 4120 9.1 

0.886540 4130 9.2 

0.889443 4140 9.2 

0.892347 4150 9.2

0.895257 4160 9.2 

0.898172 4170 9.2 

0.901092 4180 9.3 

0.9040i7 4190 9.3 

0.906946 4200 9.3

0.909879 4210 9.3 

0.9128i7 4220 9.4 

0.915759 4230 9.4 

0.918705 4240 9.4 

0.921655 4250 9.4

0.9246i3 4260 9.4 

0.927571 4270 9.5 

0.930537 4280 9.5 

0,933506 4290 9.5 

0.936480 4300 9.5

0,939459 4310 9.6 

0.942441 4320 9.6 

0.945430 4330 9.6 

0.948422 4340 9.6 

0.951420 4350 9.6

0.9544i9 4360 9.7 

0.957428 4370 9.7 

0.960438 4380 9.7 

0.963453 4390 9.7 

0.966472 4400 9.8

0.969496 4410 9.8 

0.972527 4420 9.8 

0.9755&2 4430 9.8 

0.978598 4440 9.8 

0.981642 4450 9.9

0.984690 4460 9.9 

0.987743 4470 9.9 

0.9908oo 4480 9.9 

0.993862 4490 10.0 

0.996930 4500 10.0

^207/^35

Age

D,, Number Ratio Error of +

years

48.32153 4010 90.0 

48.80331 4020 90.2 

49.28987 4030 90.4 

49.781i2 4040 90.7 

50.27722 4050 90.9

50.778i7 4060 9U 

5X28396 4070 9X3 

51.79474 4080 9X6 

52.31046 4090 9X8 

52.83127 4100 92.0

53.357i7 4110 92.2 

53,888i6 4120 92.5 

54.42438 4130 92.7 

54.96579 4140 92.9 

55.51254 4150 93,1

56.06464 4160 93.4 

56.62207 4170 93.6 

57.185oi 4180 93.8 

57.75338 4190 94.0 

58.32736 4200 94.2

58,90696 4210 94.5 

59.492i5 4220 94.7 

60,083i2 4230 94.9 

60.67980 4240 95.1 

6X28238 4250 95.4

61.89085 4260 95.6 

62.505i9 4270 95.8 

63.12560 4280 96.0 

63.752oi 4290 96.3 

64.38459 4300 96,5

65.02336 4310 96.7 

65.66830 4320 96.9 

66.319&2 4330 97.2 

66.97722 4340 97.4 

67.64132 4350 97.6

68.31191 4360 97.8 

68.98897 4370 98.1 

69.67272 4380 98.3 

70.36308 4390 98.5 

7X06025 4400 98.7

7X76425 4410 99.0 

72.47503 4420 99.2 

73.19284 4430 99,4 

73.91758 4440 99.6 

74.64949 4450 99.9

75.38854 4460 100.1 

76.13473 4470 100.3 

76.88829 4480 100.5 

77.649i4 4490 100.8 

78.41750 4500 10X0

N 207/N206

Age

D . Number ~ Ratio . . Error

°f + 

years ~*

0,411844 4010 135> 

0.414564 4020 135.6 

0.417306 4030 135.8 

0.420064 4040 136.0 

0.422845 4050 136.2

0.425646 4060 136,5 

0.428465 4070 136,7 

0,431306 4080 136.9 

0,434167 4090 137.2 

0.437050 4100 137.4

0.439952 4110 137.6 

0.442875 4120 137.8 

0.445821 4130 138.1 

0.448787 4140 138.3 

0.451776 4150 138.5

0.454786 4160 138.7 

0.457817 4170 139.0 

0.460870 4180 139.2 

0.463945 4190 139.4 

0.467043 4200 139.6

0.470163 4210 139.9 

0.473306 4220 140.1 

0.476472 4230 140.3 

0.479660 4240 140.6 

0.482873 4250 140.8

0.486107 4260 14X0 

0.489367 4270 14X2 

0.492649 4280 141.5 

0.495955 4290 14X7 

0.499286 4300 14X9

0.502640 4310 142.2 

0.506020 4320 142,4 

0.509423 4330 142.6 

0.512851 4340 142.8 

0.516304 4350 143.1

0.519784 4360 143.3 

0.523286 4370 143,5 

0.5268i6 4380 143.8 

0.530371 4390 144.0 

0.533953 4400 144.2

0.537561 4410 144.4 

0.541193 4420 144.7 

0.544853 4430 144.9 

0.548541 4440 145.1 

0.552255 4450 14^4

0.555996 4460 145.6 

0.559763 4470 145.8 

0.563560 4480 146.0 

0.567383 4490 146.3 

0.571234 4500 146.5

N2 08/N2 3 2

Age

D Number Ratio Error of +

yearr

0,2162io 4010 197.7 

0.216803 4020 198.2 

0.217397 4030 198.7 

0.217994 4040 199.2 

0.218587 4050 199.6

0.219183 4060 200.1 

0.219776 4070 200.6 

0.220372 4080 20X1 

0.220969 4090 201.6 

0.221563 4100 202.1

0.222160 4110 202.6 

0.222758 4120 203.1 

0.223355 4130 203.6 

0.223952 4140 204.1 

0.224550 4150 204.6

0.225147 4160 205.1 

0,225745 4170 205^6 

0.226343 4180 206,1 

0.226942 4190 206,5 

0.227542 4200 207.0

0.228142 4210 207.5 

0.228741 4220 208.0 

0.229341 4230 208.5 

0.229941 4240 209.0 

0,230542 4250 209.5

0.231142 4260 210.0 

0,231745 4270 210.5 

0.232345 4280 211.0 

0.232948 4290 21X5 

0.233549 4300 212,0

0.234150 4310 212.5 

0,234753 4320 213.0 

0.235356 4330 213.5 

0.235960 4340 213.9 

0.236563 4350 214.4

0.2371&7 4360 214.9 

0.237771 4370 215,4 

0.238375 4380 215.9 

0.238980 4390 216.4 

0.239584 4400 216.9

0,240190 4410 217.4 

0.240796 4420 217.9 

0.241402 4430 218,4 

0,2420o7 4440 218.9 

0.2426i4 4450 219.4

0.243221 4460 219.9 

0.243828 4470 220.4 

0.244435 4480 220.8 

0.245044 4490 22X3 

0.245651 4500 22X8
TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES

4515-5250

39

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

N 206/N 238

Age

Ratio Nufer Error

of +

years

1.001538 4515 10,0 

1006158 4530 10.0 

1.010789 4545 10.1 

1.015429 4560 10.1 

1020080 4575 10.1

1024745 4590 10.2 

1029416 4605 10.2 

I0341oo 4620 10.2 

1038795 4635 10.3 

1043499 4650 10.3

1048218 4665 10.3 

1052944 4680 10.4 

1057683 4695 10.4 

1062431 4710 10.4 

1067192 4725 10.5

1.071963 4740 10.5 

1,076746 4755 10.5 

1081538 4770 10,6 

1086344 4785 10.6 

1091157 4800 10.6

1095986 4815 10.7 

1100823 4830 10.7 

1105671 4845 10.7 

1110532 4860 10.8 

1115402 4875 10.8

1120283 4890 10.8 

1125177 4905 10.9 

1130084 4920 10.9 

l,1350oi 4935 10.9 

1139928 4950 110

1.144866 4965 HO 

1149817 4980 11.0 

1154777 4995 HI 

1159751 5010 111 

1164737 5025 11.1

1169733 5040 11.2 

1174743 5055 112 

1179759 5070 11.2 

1184791 5085 113 

1189836 5100 113

1.194887 5115 11,3 

1199953 5130 114 

1.205033 5145 114 

1210122 5160 114 

1215222 5175 115

1.220333 5190 115 

1225459 5205 H5 

1230598 5220 116 

1.235744 5235 116 

1240905 5250 11.6

^207/^35

Aee

D Number Ratio Error

° f ± 

years

79.5840 4515 1013 

80.7678 4530 1017 

819688 4545 102.0 

83.1876 4560 102.3 

84,4243 4575 102.7

85.6790 4590 103.0 

86.9524 4605 103.3 

88.2443 4620 103.7 

89.5553 4635 104.0 

90.8854 4650 104.3

92.2351 4665 104.7 

93.6047 4680 105.0 

94.9943 4695 105.4 

96.40 4 5 4710 105.7 

97.8352 4725 106.0

99,2870 4740 106.4 

100.7602 4755 106.7 

102,2550 4770 107.0 

I03.77i8 4785 107.4 

105,3107 4800 107.7

106.8723 4815 108.1 

108.4569 4830 108.4 

110.0647 4845 108.7 

1116963 4860 109.1 

113.35i6 4875 109.4

115.03i4 4890 109.7 

116.7358 4905 110.1 

118.4652 4920 110.4 

120.22o2 4935 110.7 

122.0007 4950 1111

123.807 5 4965 1114 

125.6409 4980 1118 

127.50ii 4995 112.1 

129.3888 5010 112.4 

131304 o 5025 112.8

133.2474 5040 113,1 

135.2195 5055 113.4 

137,22o4 5070 113.8 

139.2508 5085 114,1 

14131io 5100 114.4

143.40i3 5115 114.8 

145.5226 5130 115.1 

147.6748 5145 115.5 

149.8588 5160 115.8 

152.0748 5175 116.1

154.3233 5190 116.5 

156.6049 5205 116.8 

158.92oo 5220 117.1 

1612692 5235 117.5 

163.6527 5250 117,8

W 207/W 206

Age

n . Number ^ Ratio . Error

°f + 

years ~

0.577064 4515 146.9 

0.582959 4530 147,2 

0.5889i7 4545 147,5 

0.594943 4560 147.9 

0.601034 4575 148,2

0.607190 4590 148.6 

0.6134i8 4605 148,9 

0.619712 4620 149.3 

0.626076 4635 149.6 

0,6325ii 4650 150,0

0.6390i4 4665 150.3 

0,645592 4680 150.7 

0,652241 4695 1510 

0.6589&5 4710 1513 

0.6657&2 4725 1517

0,672634 4740 152.0 

0.679582 4755 152.4 

0.686608 4770 152.7 

0.6937io 4785 153,1 

0.700892 4800 153.4

0.708152 4815 153.8 

0.715494 4830 154.1 

0,7229i7 4845 154.5 

0.730422 4860 154.8 

0.7380io 4875 155.2

0,745683 4890 155.5 

0,753441 4905 155.9 

0.761283 4920 156,2 

0.7692i4 4935 156.6 

0.777233 4950 156,9

0.785341 4965 157.3 

0.793539 4980 157.6 

0.801829 4995 158.0 

0,8l02io 5010 158.3 

0,818684 5025 158.7

0.827252 5040 159.0 

0.8359i5 5055 159.4 

0.844678 5070 159.7 

0,853536 5085 160.1 

0.862491 5100 160,4

0,871550 5115 160,8 

0,880708 5130 1611 

0.889966 5145 1615 

0,899330 5160 1618 

0.908798 5175 162.2

0.918373 5190 162.5 

0.928053 5205 162.9 

0.937839 5220 163.2 

0.947739 5235 163.6 

0.957747 5250 163.9

N208/N232

Age

D Number ^ Ratio Error of +

years

0,246564 4515 222.6 

0,247475 4530 223.3 

0,248389 4545 224.0 

0,249304 4560 224.8 

0.250220 4575 225.5

0.251134 4590 226,3 

0.252051 4605 227.0 

0.2529&7 4620 227.7 

0,253887 4635 228.5 

0,254805 4650 229.2

0,255723 4665 230,0 

0,256643 4680 230.7 

0.257564 4695 2314 

0.258486 4710 232.2 

0,259407 4725 232.9

0.260330 4740 233.7 

0,261252 4755 234,4 

0,262175 4770 235.1 

0.2631oo 4785 235.9 

0.264026 4800 236,6

0.264951 4815 237.4 

0.265879 4830 238,1 

0.266806 4845 238.8 

0.267734 4860 239.6 

0.268662 4875 240.3

0.269592 4890 2411 

0,270521 4905 2418 

0.271451 4920 242.5 

0.272383 4935 243.3 

0.273316 4950 244.0

0.274247 4965 244.8 

0,275182 4980 245.5 

0.276115 4995 246.2 

0.277050 5010 247.0 

0,277985 5025 247.7

0,278921 5040 248.5 

0.279858 5055 249.2 

0,280795 5070 249.9 

0,281734 5085 250.7 

0,282673 5100 2514

0.283613 5115 252.1 

0.284553 5130 252.9 

0.285493 5145 253.6 

0.286436 5160 254.4 

0.287377 5175 255.1

0.288319 5190 255.8 

0.289263 5205 256^6 

0,2902 07 5220 257.3 

0.291154 5235 258.1 

0.2921oo 5250 258.8
40 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

5265-6000

Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes

^206/^238

Age

Ratio Error of +

years

3,246076 5265 11,7

1.2512s 9 5280 11.7

1,2564s? 5295 117

1.261664 5310 11.8

3,266883 5325 1X8

X2721i6 5340 1X8

X277361 5355 1X9

X282616 5370 1X9

1.287885 5385 1X9

1.293166 5400 12.0

X298458 5415 12.0

3,303764 5430 12.0

X309080 5445 12.1

X3144ii 5460 12.1

1,319752 5475 12.1

X325105 5490 12.2

1.330471 5505 12,2

X335850 5520 12.2

1.3412 4 3 5535 12.3

1.346645 5550 12.3

X352062 5565 12.3

1.357491 5580 12.4

X362931 5595 12.4

1.368385 5610 12,4

3,373851 5625 12.5

1.379330 5640 12.5

X384823 5655 12.5

1,390327 5670 12.6

X395843 5685 126

1.401373 5700 12.6

X4069i5 5715 12.7

X412469 5730 12,7

X418041 5745 12,7

X423620 5760 12.8

1,429214 5775 12.8

1,434819 5790 12.8

X440439 5805 12.9

1.446073 5820 12.9

1.451718 5835 12.9

X457377 5850 13.0

1.463050 5865 13.0

1.468733 5880 13,0

1.474434 5895 13,1

1.480143 5910 13.1

1.485867 5925 13.1

X491604 5940 13.2

X497355 5955 13.2

X503120 5970 13.2

X508897 5985 13.3

X514686 6000 13.3

"2077*235

Age

D Number Ratio Error of 4.

years

166.0713 5265 118,1

168.5255 5280 118.5

17X0157 5295 118.8

173,5424 5310 119.2

176.1064 5325 119.5

178.7079 5340 119.8

181.3477 5355 120.2

184.0262 5370 120,5

186.7440 5385 120,8

189.5020 5400 12X2

192.30o2 5415 12X5

195.1398 5430 12X9

198.02o8 5445 122.2

200.9442 5460 122.5

203.9108 5475 122.9

206.9207 5490 123.2

209.9750 5505 123,5

213.0740 5520 123.9

216.2185 5535 124,2

219.4094 5550 124.5

222.6469 5565 124.9

225.9323 5580 125.2

229.2657 5595 125,6

232.6480 5610 125.9

236.0802 5625 126,2

239.5627 5640 126.6

243.09&5 5655 126.9

246.6820 5670 127.2

250.32o2 5685 127,6

254.0120 5700 127.9

257.7578 5715 128.2

26X5590 5730 128.6

265.4157 5745 128.9

269.3290 5760 129.3

273.30oi 5775 129.6

277.3292 5790 129.9

281.4179 5805 130.3

285.5662 5820 130.6

289.7756 5835 130.9

294.0470 5850 13X3

298.3809 5865 13X6

302.7788 5880 13X9

307,24o9 5895 132.3

31X7686 5910 132.6

316.3631 5925 133.0

321.0249 5940 133.3

325.7554 5955 133.6

330.5550 5970 134.0

335.4252 5985 134,3

340.3672 6000 134.6

N 207/N206

Age

 Number ,-, Ratio . Error of +

years 

0,967868 5265 164.3

0.978103 5280 164,6

0,988449 5295 165.0

0,9989i3 5310 165.3

X009496 5325 165.7

1.020194 5340 166.0

X0310i4 5355 166.4

X041955 5370 166.7

I,0530i8 5385 167.1

X064205 5400 167.4

1.075518 5415 167.8

X086958 5430 168.1

X098527 5445 168.5

1.110223 5460 168.9

3,122054 5475 169.2

X1340i7 5490 169.6

3,1463.15 5505 169.9

1.158347 5520 170.3

X170715 5535 170.6

X183227 5550 17X0

X195876 5565 17X3

1.208669 5580 17X7

X221606 5595 172.0

1.234687 5610 172.4

X2479i8 5625 172.7

X261296 5640 173,1

X274825 5655 173.5

X288506 5670 173.8

X302343 5685 174.2

X316335 5700 174,5

X330485 5715 174.9

X344797 5730 175^2

X359264 5745 175.6

X3739oo 5760 175.9

X3887oo 5775 176,3

X403668 5790 176.7

X418805 5805 177.0

X4341ii 5820 177.4

1.449591 5835 177,7

X465247 5850 178.1

X481078 5865 178.4

X497092 5880 178.8

X513282 5895 179.1

X529659 5910 179.5

1.546222 5925 179.9

X562972 5940 180.2

X5799i2 5955 180.6

X59704 i 5970 180.9

X614366 5985 18X3

X631891 6000 18X6

N 208/N232

Age

D . Number _ Ratio Error of +

years

0.293046 5265 259.5

0,293992 5280 260.3

0,294939 5295 26X0

0.295890 5310 261,8

0.296838 5325 262,5

0.297788 5340 263.2

0.298738 5355 264.0

0.299689 5370 264.7

0.300642 5385 265.5

0.301595 5400 266.2

0.302547 5^15 266.9

0.303501 5^30 267,7

0.304456 5445 268.4

0.305413 5460 269.2

0.306369 5475 269.9

0.307324 5490 270.6

0.308282 5505 271,4

0.309240 5520 272.1

0.310201 5535 272.9

0.311160 5550 273,6

0.312119 5565 274.3

0.313080 5580 275.1

0.314042 5595 275.8

0.315005 5*10 276.5

0.315968 5*25 277.3

0.316932 5*40 278.0

0.317896 5*55 278.8

0.318862 5*70 279,5

0.319829 5685 280.2

0.320794 5700 28X0

0.321763 5715 28X7

0.322730 5730 282.5

0.323699 5745 283.2

0.324669 5760 283.9

0.325639 5775 284,7

0.326609 5790 285.4

0.327581 5805 286.2

0.328554 5820 286,9

0,329528 5835 287.6

0.3305oo 5850 288.4

0.331474 5865 289.1

0.332450 5880 289.9

0.333427 5895 290.6

0.334404 5910 29X3

0.335381 5925 292.1

0.336359 5940 292,8

0.337338 5955 293,6

0.338317 5970 294.3

0.339298 5985 295.0

0.340279 6000 295,8

U. S. GOVERNMENT PRINTING OFFICE: 1959 O 485342