Evening star. [volume] (Washington, D.C.) 1854-1972, 1936-10-29

Earth wears a 1000 mile-thick UNDER
shirt Of o rare mineral.
DR.. L. H. Adams, physical chemist OF
the Carnegie Institution Of Washington,
last night described experiments at the
Geophysical Laboratory here which indl-
cate that between the thin crust and
heavy core of the planet there is an
enormous intermediate zone of rock
known as dunite. 1t is a very heavy
greeniSh- yellow Stone-a compound OF
magnesium silicate and iron silicate-
which is known only from very rare
deposits on the earth's surface.
1t has been known for some time that
there is a remarkable change in the
speed of earthquake waves, from about
81 to miles a second, at about 80
miles below the surface. Tests at the
geophysical laboratory indicate that there
are only two kinds of rocks known which
could support so high velocity at the
moderate preSSures prevailing at this
depth. One is dunite and the other
very similar mineral known as eclogite.
Other evidence. however. makes dunlte
the most probable. The earthquake
waves continue at these tremendous
speeds to depth of about 1000 miles.
Above the dunite Sub-Stratum, DR..
Adams pointed out in lecture at the
Carnegie Institution, is the relatively
very thin crust, from Is miles to 81 miles
in depth. which might be compared to
the earthS outer garment. 1t is in two
layers, granite above and baSalt below.
From geological studies, DR.. Adams
said, it long has been known that the
accessible part of the crust consists
largely of granite. These, however, ex-
tended to only very superficial depths.
Experiments at the geophysical labora-
tory show that the velocity OF longi-
tudinal vibrations in granite Is about
81 miles a second, almost exactly that
found by seismologists for earthquake
waves running through the superficial
layer of the planet. This confirms the
findings of the biologists for much
greater depths than it is possible to 60
with shovel or drill.
This granite layer, DIR. Adams said,
varies greatly in thickness from place to
place. In continental areas it ranges
from miles to almost 20 miles in depth.
while in the great ocean basins it appears
to be missing entirely. Underneath the
granite layer the crust, as indicated by
the velocity of earthquake waves passing
through the region, is basaltic in compo-
Siti0n. There Is some evidence for a
transition layer of both granite and
basalt, but it has been impossible to de-
termine the existence of this.
BY a series Of deductions from earth
quake wave speeds and other evidence,
DIR. Adams said, the conclusion has been
reached that the earth's core, having
diameter somewhat more than half that
OF the planet as a whole, consists OF
very heavy Substance-probably metallic
iron or Michel iron. This is quite different
from iron known as the surface. AT its
center it is under q pressure OF about
100000 pounds to the square inch,
condition rendering 1t non-magnetic, so
that it has no appreciable effect on the
earth's magnetism.
Although 1t Is certain that the core is
very hot, according to DR.. Adams. it has
not been possible to arrive at very
satisfactory estimate Of its temperature.
It appears to be well over 5000 degrees
Fahrenheit.
From observations on the tidal defor-
nations Of the surface, he said, the eartn
long has been known to be as rigid as
steel and from earthquake data 1t Is
found that from crust to core the rightly
increases steadily with increasing depth.
1t Is clear, therefore, that the earth as
whole Is solid. It is much harder to
decide, however, whether its substance
particularly that of the intermediate
zone, is crystalline or CLASSY.
But" DR.. Adams said, from what
information we have 1t does not seem
possible that any permanent silicate