bluuebunny/crossref_metadata_2025_split huggingface dataset:
Celebrating the age of the Earth
Authors: Knell Simon J. , Lewis Cherry L. E. 
Published: April 2008

Abstract

The age of the Earth has been a subject of intellectual interest for many centuries, even millennia. Of the early estimates, Archbishop Ussher’s famous calculation of 4004
bc
for the date of Creation represents one of the shortest time periods ever assigned to the Earth’s age, but by the seventeenth century many naturalists were sceptical of such chronologies. In the eighteenth century it was Nature that provided the record for Hutton and others.

But not all observers of geology enquired about time. Many, like William Smith, simply earned a living from their practical knowledge of it, although his nephew, John Phillips, was one of the first geologists to attempt a numerical age for the Earth from the depositional rates of sediments. For more than fifty years variations of that method prevailed as geology’s main tool for dating the Earth, while the physicists constrained requirements for a long timescale with ever more rigorous, and declining, estimates of a cooling Sun and Earth.
In 1896 the advent of radioactivity provided the means by which the Earth’s age would at last be accurately documented, although it took another sixty years. Since that time ever more sophisticated chronological techniques have contributed to a search for the oldest rocks, the start of life, and human evolution. In the attempt to identify those landmarks, and others, we have greatly progressed our understanding about the processes that shape our planet and the Universe, although in doing so we discover that the now-accepted age of the Earth is but a ‘geochemical accident’ which remains a contentious issue.
Genesis and geochronology: the case of John Phillips (1800–1874)
Authors: Morrell Jack 
Published: April 2008

Abstract

In 1841 John Phillips proposed that there were three great periods of past life on the Earth, namely the Palaeozoic, the Mesozoic and the Cainozoic, terms which are still used today. This was by no means Phillips’ sole contribution to geochronology and this paper examines his evolving views on it over a span of forty years. In the 1820s he adopted the Deluge as a notion which reconciled Genesis and geology. From the 1830s he adopted a liberal Christian position, which saw attempts at such reconciliation as futile and dangerous, and incurred the wrath of so-called scriptural geologists. From 1853 to his death, Phillips was a public figure as successively deputy reader, reader, and professor of geology in the University of Oxford. He was also president of the Geological Society from 1858 to 1860. The publication of Darwin’s
Origin of Species
(1859) not only provoked him to reaffirm his liberal Christian beliefs but also induced him to give greater attention to geochronology as a weapon to be used against Darwinian evolution.
John Joly (1857–1933) and his determinations of the age of the Earth
Authors: Wyse Jackson Patrick N. 
Published: April 2008

Abstract
John Joly (1857–1933) was one of Ireland’s most eminent scientists of the late nineteenth and early twentieth centuries who made important discoveries in physics, geology and photography. He was also a respected and influential diplomat for Trinity College, Dublin, and various Irish organizations, including the Royal Dublin Society. Measuring the age of the Earth occupied his mind for some considerable time — a problem he was to address using a diverse range of methods. His sodium method of 1899, for which he is best known, was hailed by many as revolutionary, but it was later superseded by other techniques, including the utilization of radiometric dating methodologies. Although Joly himself carried out much research in this area, he never fully accepted the large age estimates that radioactivity yielded. Nevertheless, Joly’s work in geochronology was innovative and important, for it challenged earlier methods of arriving at the Earth’s age, particularly those of Lord Kelvin. Although his findings and conclusions were later discredited, he should be remembered for his valuable contribution to this important and fundamental debate in the geological sciences.
Is the Earth too old? The impact of geochronology on cosmology, 1929–1952
Authors: Brush Stephen G. 
Published: April 2008

Abstract
Estimates of the Earth’s age have had significant impacts, not only on geology but also on biology, astronomy and biblical creationism. In the 1930s and 1940s, the age of the universe as estimated from the expanding universe was less than 2000 million years, but the age of the Earth as estimated from radiometric dating was perhaps as great as 3000 million years. Astronomers responded to this contradiction in at least three different ways. Some cosmologists favoured Georges Lemaître’s relativistic model, in which the universe remains about the same size for an indefinite period of time before starting its present stage of expansion. Since theories of the origin of the solar system that were popular in the early 1930s assumed an encounter between the Sun and another star, it seemed plausible that the Earth could have been formed around this epoch of ‘cosmic congestion’. Edwin P. Hubble, generally regarded as the founder of the expanding-universe theory because of his discovery of the redshift-distance law, doubted that redshifts are actually due to velocities, and seemed to prefer a non-expanding model, though he emphasized that the correct interpretation of the redshifts of distant galaxies was still an open question up until the time of his death in 1953. Fred Hoyle, Hermann Bondi and Thomas Gold proposed a ‘steady-state’ cosmology: the universe has always existed, so there is no conflict between its (infinite) age and that of the Earth. The discrepancy was finally resolved in the 1950s when astronomers revised their distance scale and boosted the age of the universe to 10 000 million years or more. The current agreement between geologists and astronomers again leaves creationists with no scientific support at all for their claim that both the Earth and universe were created only about 10 000 years ago.
The age of the Earth in the twentieth century: a problem (mostly) solved
Authors: Dalrymple G. Brent 
Published: April 2008

Abstract
In the early twentieth century the Earth’s age was unknown and scientific estimates, none of which were based on valid premises, varied typically from a few millions to billions of years. This important questions was answered only after more than half a century of innovation in both theory and instrumentation. Critical developments along this path included not only a better understanding of the fundamental properties of matter, but also: (a) the suggestion and first demonstration by Rutherford in 1904 that radioactivity might be used as a geological timekeeper; (b) the development of the first mass analyser and the discovery of isotopes by J. J. Thomson in 1914; (c) the idea by Russell in 1921 that the age of a planetary reservoir like the Earth’s crust might be measured from the relative abundances of a radioactive parent element (uranium) and its daughter product (lead); (d) the development of the idea by Gerling in 1942 that the age of the Earth could be calculated from the isotopic composition of a lead ore of known age; (e) the ideas of Houtermans and Brown in 1947 that the isotopic composition of primordial lead might be found in iron meteorites; and (f) the first calculation by Patterson in 1953 of a valid age for the Earth of 4.55 Ga, using the primordial meteoritic lead composition and samples representing the composition of modern Earth lead. The value for the age of the Earth in wide use today was determined by Tera in 1980, who found a value of 4.54 Ga from a clever analysis of the lead isotopic compositions of four ancient conformable lead deposits. Whether this age represents the age of the Earth’s accretion, of core formation, or of the material from which the Earth formed is not yet known, but recent evidence suggests it may approximate the latter.
Compaction experiments on wet calcite powder at room temperature: evidence for operation of intergranular pressure solution
Authors: Zhang X. , Salemans J. , Peach C. J. , Spiers C. J. 
Published: April 2008

Abstract

Dead weight uniaxial compaction creep experiments were carried out on fine-grained, super-pure calcite (<74 μm) at room temperature and applied effective stresses of 1–4 MPa. All samples were pre-compacted dry at a stress of 8 MPa, for 30 minutes, to obtain a well-controlled initial porosity. The samples were then wet-compacted under ‘drained’ conditions with pre-saturated solution as pore fluid. Control experiments, which were done either dry or with chemically inert pore fluid, showed negligible compaction. However, samples tested with saturated solution as pore fluid showed easily measurable compaction creep. The compaction strain rate decreased with increasing strain and increasing grain size, and increased with increasing applied stress. Addition of Mg
2+
ions to the saturated solution dramatically inhibited compaction. From the literature, Mg
2+
ions are known to inhibit calcite precipitation. By comparison with a theoretical model for intergranular pressure solution in calcite, the observed mechanical behaviour and the way that compaction responded to the pore fluid chemistry suggest that, under our experimental condition, intergranular pressure solution is the mechanism of the deformation and that precipitation is likely to be the rate-limiting step.
Numerical modelling of pressure solution in sandstone, rate-limiting processes and the effect of clays
Authors: Gundersen E. , Dysthe D. K. , Renard F. , Bjørlykke K. , Jamtveit B. 
Published: April 2008

Abstract
Pressure solution is an efficient mechanism for ductile deformation and local mass transport in the upper crust. In this paper we model pressure solution as a mechanism involving four steps: (1) dissolution at the grain contacts; (2) diffusion of solutes through fluid films at the contact between two grains; (3) transport of solutes by diffusion through the pore fluid into other adjacent open pores; and (4) precipitation on the surface of grains at their contact with the pore fluid. In this study we constrain under which conditions pressure solution is limited by one of the four processes: dissolution; contact diffusion; precipitation; and global diffusion. From our model of pressure solution, based on thermodynamic relationships we derive three dimensionless numbers which represent the competetion between the four mentioned processes. With these numbers we can define the crossover from a situation where one process acts as the limiting process to a new situation controlled by another process. We also see how the different rate-limiting processes influence the amount of mass transported during the compaction process. In addition we study the effect of clays, as it has been suggested that these minerals speed up the rate of pressure solution. We propose two models, a chemical related and a mechanical model for how the clay particles may affect the dissolution process of quartz.
Effects of stress on the anisotropic development of permeability during mechanical compaction of porous sandstones
Authors: Zhu Wenlu , Montési Laurent G. J. , Wong Teng-Fong 
Published: April 2008

Abstract

To investigate the influence of stress on permeability anisotropy during mechanical compaction, a series of triaxial compression experiments with a new loading configuration called hybrid compression were conducted on three porous sandstones. The effective mean and differential stresses in hybrid compression tests were identical to those in conventional triaxial extension tests. Permeability was measured along the axial direction in both hybrid compression and conventional extension tests, which corresponds to flow along the maximum principal stress direction in the former case and the minimum principal stress direction in the latter case. Since their loading paths coincide, the comparison of permeability values from the two types of tests provides quantitative estimates of the development of permeability anisotropy as a function of effective mean and differential stresses. Our data show that the permeability evolution is primarily controlled by stress. Before the onset of shear-enhanced compaction
C
*, permeability and porosity reduction are solely controlled by the effective mean stress, with negligible stress-induced anisotropy. With the onset of shear-enhanced compaction and initiation of cataclastic flow, the deviatoric stress induces enhanced permeability and porosity reduction. The permeability tensor may show significant anisotropy. Our data indicate that the maximum principal component of permeability tensor
k
1
is parallel to the maximum principal stress σ
1
, and the minimum principal component
k
3
is parallel to the minimum principal stress σ
3
. During the initiation and development of shear-enhanced compaction,
k
1
can exceed
k
3
by as much as two orders of magnitude. With the progressive development of cataclastic flow, changes of permeability and porosity become gradual again, and the stress-induced permeability anisotropy diminishes as
k
1
and
k
3
gradually converge. Our data imply that permeability can be highly anisotropic in tectonic settings undergoing cataclastic flow, inducing the fluid to flow preferentially along conduits subparallel to the maximum compression direction. However, this development of permeability anisotropy is transient in nature, becoming negligible with an accumulation of strain of about 10%. The anisotropic development of permeability in a lithified rock is dominantly controlled by microcracking and pore collapse. This is fundamentally different from the mechanisms active in unconsolidated materials such as sediments and fault gouges, in which the permeability evolution is primarily controlled by the development of fabric and shear localization via the accumulation of shear strain.
The numerical simulation of microstructure
Authors: Jessell Mark W. , Bons Paul D. 
Published: April 2008

Abstract
This review discusses the attempts that have been made by geologists to numerically simulate the evolution of microstructures in rocks. The strengths and weaknesses of the differing techniques are compared and equivalent materials science results are included. In particular we focus on the application of techniques that have been used to predict texture development, grain boundary geometries, deformation in one and two-phase systems and crystal growth.
Dynamic recrystallization of quartz: correlation between natural and experimental conditions
Authors: Stipp Michael , Stünitz Holger , Heilbronner Renée , Schmid Stefan M. 
Published: April 2008

Abstract

Quartz veins in the Eastern Tonale mylonite zone (Italian Alps) were deformed in strike-slip shear. Due to the synkinematic emplacement of the Adamello Pluton, a temperature gradient between 280°C and 700°C was effected across this fault zone. The resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization, subgrain rotation recrystallization and grain boundary migration recrystallization. The transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature. Differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships. Deformation temperatures are obtained from metamorphic reactions in the deformed host rock. Flow stresses and deformation temperatures are used to determine the strain rate of the Tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10
−14
s
−1
to 10
−12
s
−1
. The deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of Hirth & Tullis. Linking the microstructures of the naturally and experimentally deformed quartz rocks, a recrystallization mechanism map is presented. This map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known.
The effect of static annealing on microstructures and crystallographic preferred orientations of quartzites experimentally deformed in axial compression and shear
Authors: Heilbronner Renée , Tullis Jan 
Published: April 2008

Abstract

Quartzite samples were experimentally deformed with partial to complete dynamic recrystallization by axial compression (strain magnitude of 0.8 to 1.4) and by general shear (strain magnitude of 1.3 to 2.8) in each of the three dislocation creep regimes, and subsequently annealed with complete static recrystallization at the deformation temperature for 120 hours. The
c
-axis crystallographic preferred orientation (CPO), 3D grain size distribution, grain boundary surface shape, and misorientation density were measured before and after annealing. The effect of annealing on the CPO was minor, but the microstructure was greatly changed. All of the annealed samples were completely recrystallized. The recrystallized grain size increased by a factor of 2 to 5, and was greatest for samples deformed at lowest temperature. The grain boundary lobateness (PARIS factor) and misorientation density were reduced significantly. The CPOs for all the deformed samples were relatively unchanged by annealing, although the strengths are somewhat decreased; for sheared samples the asymmetry was preserved. The results suggest microstructural criteria for recognizing the occurrence of static annealing and for estimating the dynamically recrystallized grain size relevant for paleopiezometry from annealed samples.
Stress and deformation in subduction zones: insight from the record of exhumed metamorphic rocks
Authors: Stöckhert Bernhard 
Published: April 2008

Abstract
High pressure (HP) and ultrahigh (UHP) metamorphic rocks are exhumed from subduction zones at high rates on the order of plate velocity (cm/year). Their structural and microstructural record provides insight into conditions and physical state along the plate interface in subduction zones to depths of >100 km. Amazingly, many identified (U)HP metamorphic rocks appear not to be significantly deformed at (U)HP conditions, despite their history within a high strain rate mega-shearzone. Other (U)HP metamorphic rocks seem to be deformed exclusively by dissolution-precipitation creep. Indications of deformation by dislocation creep are lacking, apart from omphacite in some eclogites. Available flow laws for dislocation creep (extrapolated to low natural strain rates, which is equivalent to no deformation on the time scales of subduction and exhumation, i.e., 1 to 10 Ma) pose an upper bound to the magnitude of stress as a function of temperature along the trajectory followed by the rock. Although the record of exhumed (U)HP metamorphic rocks may only be representative of specific types or evolutionary stages of subduction zones, for such cases it implies: (1) strongly localized deformation; (2) predominance of dissolution-precipitation creep and fluid-assisted granular flow in the shear zones, suggesting Newtonian behaviour; (3) low magnitude of differential stress; which (4) is on the order of the stress drop inferred for earthquakes; and (5) negligible shear heating. These findings are easily reconciled with exhumation by forced flow in a low viscosity subduction channel prior to collision, implying effective decoupling between the plates.
On estimating the strength of calcite rocks under natural conditions
Authors: De Bresser J. H. P. , Evans B. , Renner J. 
Published: April 2008

Abstract
Field studies of calcite mylonites often document microstructures produced by dislocation creep. In contrast, flow laws derived from experiments predict that calcite rocks should deform mostly by diffusion creep during tectonic processes. To investigate this apparent discrepancy, we compare stresses estimated by microstructural piezometers to those obtained by extrapolation of experimentally derived flow laws. Considering shear zones from different geological settings, a clear trend is observed of increasing recrystallized grain size with increasing temperature. However, there is a large spread in grain size and associated stress. Because separate flow laws have been defined for various different marbles and limestones, the strengths predicted for a given set of conditions differ significantly. The stress estimates based on the piezometers and strength extrapolated from the various experimentally derived dislocation creep flow laws agree qualitatively, but no single flow law predicts all the palaeostress estimates. Even if experimental data are disregarded, the field observations are not consistent with a hypothetical law for Coble creep; they are consistent with a power law for dislocation creep, but only if the material constants are different from those currently determined in laboratory experiments.
Deformation of the continental lithosphere: Insights from brittle-ductile models
Authors: Brun Jean-Pierre 
Published: April 2008

Abstract
2D deformation experiments on multilayer models of a brittle-ductile lithosphere are reviewed. The experimental method consists of simulating simplified strength profiles which incorporate brittle (frictional) and ductile (viscous) rheologies with gravity forces. A selection of models built with sand and silicone putties to represent brittle and ductile lithosphere layers, respectively, is used to illustrate the effects of variations in strength profiles on deformation patterns. Models of extension first consider lithosphere necking and the development of narrow rifts, with application to continental rifts and passive margins, and, second, lithosphere spreading with application to the development of wide rifts and core complexes. Models of compression compare sandbox-type and brittle-ductile multilayer-type experiments. Results are applied to mountain belt formation and, in particular, to the Pyrenees and the western Alps. Both extensional and compressional experiments demonstrate that the presence/absence of a sub-Moho brittle mantle and the coupling/decoupling between brittle and ductile layers play a dominant role on localized versus distributed deformation, at lithosphere scale.
Evidence for steady fault-accommodated strain in the High Himalaya: progressive fault rotation of the southern Tibet detachment system in NW Bhutan
Authors: Wiesmayr G. , Edwards M. A. , Meyer M. , Kidd W. S. F. , Leber D. , Häusler H. , Wangda D. 
Published: April 2008

Abstract

We present fault analyses from the exhumed middle crustal slab of the High Himalaya in eastern Lunana in NW Bhutan. Fault planes from within two-mica, tourma-line-bearing leucogranites, leucogranitic rocks and migmatites indicate a complex brittle fault pattern with two distinct fault groups. A first group of faults (D
1
) characterized by chlorite, quartz and tourmaline slickenfibres is mainly defined by steeply SSE-dipping oblique-slip normal faults, and by shallowly NNW-dipping normal faults. A second, younger group of faults (D
2
) characterized by cataclasis products comprises strike-slip faults displaying conjugate patterns and E- and W-dipping conjugate normal faults, all which indicate E-W extension. Cross-cutting relationships amongst the D
1
fault group demonstrate that progressively steeper members of the fault group become younger within the NNW-dipping faults and become older within the SSE-dipping faults. These are all post-dated by the D
2
fault group. The D
1
fault group indicates that the slab experienced ongoing NNW-SSE extension (i.e. flow) via brittle fault accommodation, contemporaneous with fault rotation. This may reflect rotation of the entire upper orogen due to movement over deeply located major ramp structures formed by out-of-sequence thrusting (Kakhtang Thrust) within the High Himalayan Slab of the Bhutan Himalaya.