Geology Reading

Oxygen and Evolution

-Rise of atmospheric oxygen cct during the Precambrian eon tied to biological evolution. Here we examine evidence for changes in O2 cct and their biological causes and effects during the phanerozoic. Evidence: mainly geochemical cycles of CARBON and SULFUR. The weathering of these results in O2 consumption. Their burial results in O2 production (excess of global photosynthesis over global resp). Evolution of large vascular plants --> burial of oxygen --> increased O2 production --> burial of lignin --> formation of coal deposits --> increased wildfires ~the effects of O2 cct on modern physiology and development still poorly understood: -Of the existing studies, many have used: Drosophila melanogaster to study O2 effects. FOUR major events illustrate effects of high O2 levels on evolution: 1) origin of first body plans 2) conquest of land animals 3) development of gigantism 4) increase in mammalian body size Effects of dropping O2: 1) three extinctions it appears... Let's strive for better O2 modeling!

Chicxulub Crater: A Possible Cretaceous/Tertiary Boundary Impact Crater on the Yucatan Peninsula, Mexico,

http://adsabs.harvard.edu/abs/1991Geo....19..867H We suggest that a buried 180-km-diameter circular structure on the Yucatán Peninsula, Mexico, is an impact crater. Its size and shape are revealed by magnetic and gravity-field anomalies, as well as by oil wells drilled inside and near the structure. The stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with, and overlain by, breccias that contain evidence of shock metamorphism. The andesitic rocks have chemical and isotopic compositions similar to those of tektites found in Cretaceous/Tertiary (K/T) ejecta. A 90-m-thick K/T boundary breccia, also containing evidence of shock metamorphism, is present 50 km outside the crater's edge. This breccia probably represents the crater's ejecta blanket. The age of the crater is not precisely known, but a K/T boundary age is indicated. Because the crater is in a thick carbonate sequence, shock-produced CO2 from the impact may have caused a severe greenhouse warming. Subsurface stratigraphy of northern yucatan peninsula known from petroleum exploration drillholes. Andesitic glass, breccia, sandstone interbedded with marlstone, shale, and sometimes dolomitic limesstones. Petrology: to investigate the origin of the andesitic igneous rocks and carbonate breccias using optical microscopy, X-ray diffraction and electron-micoprobe techniques. Quartz grains in these xenoliths exhibit multiple sets of planar elements that are indicative of schock metamorphism. Believe that the geophysical, stratigraphic, and petrologic evidence strongly indicate the presence of a buired impact crater.

"Dynamic Deformation of Volcanic Ejecta from the Toba Caldera: Possible Relevance to Cretaceous/Tertiary Boundary Phenomena"

http://geology.gsapubs.org/content/14/5/380.full.pdf Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development in plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. basically shock stresses of large magnitudes don't need to originate from extraterrestrial things. "Merits further exploration"

"Evidence for a Strong San Andreas Fault"

http://geology.gsapubs.org/content/28/2/163.full.pdf Stress measurements in deep boreholes have universally shown that stresses in the Earth's crust are in equilibrium with favorably oriented faults with friction coeff in the range 0.6-0.7 and with nearly hydrostatis pore-oressure gradients. Beacuse the lack of any fault-adjacent heat-flow anomaly as predicted by a conductive model of frictional heating, the San Andreas fault has long been thought to be an exception. - far weaker than the standard case. Borehole stress measurements near the San Andreas fault have failed to confirm this weak-fault hypothessis, being either inconclusive or in conflict with it. Directions of maximum horizontal stresses reported to be nearly fault normal in central CA are now known not to be regional stresses reported to be active folding within folds that have been rotated 20-30 degrees clockwise from their original orientations.The sense of this rotation is opposite to that expected from the weak-fault hypothesis. If the adjacent minor thrust faults are assumed to obey Byerlee Friction, the crustal-average sheer stress on the San Andreas in that region must be in the range 100-160 MPa, regardless of pore pressure in the fault. CONCLUSION: The heat-flow model is flawed, probably in its assumption that all heat transfer is governed by conduction.

Chicxulub - The non-smoking gun

http://geoweb.princeton.edu/people/keller/kellerreply.pdf Jan Smit questioned this evidence in CCNET of Oct. 9, 2003. He claimed that the varied evidence in Mexico presented by Keller and her collaborators can all be explained by the mechanisms of "tsunamis, mass wasting, slumping and earthquakes triggered by the impact" which make explanation of the KT sedimentary deposits "very complicated indeed." -multiple spherule layers indicate single event could not be the case. They also predate the KT age -further drilling into chicxulub indicate pre-KT age The evidence from sedimentology and microfossils of Yaxcopoil-1 indicates that the critical 50 cm interval between the breccia and KT boundary was deposited under normal pelagic condition during the last 300 ky of the Maastrichtian. Yaxcopoil-1 is not alone. Limestones containing late Maastrichtian planktic foraminifera have been reported from sediments overlying the impact breccia in wells T1, Y6 and C1 (14) - a fact also supported by e-log correlations (15). The new evidence from Yaxcopoil-1, combined with the spherule ejecta evidence from NE Mexico, indicates that the Chicxulub impact predated the KT boundary by about 300k y. Chicxulub therefore was not the cause for the KT mass extinction. The KT impact crater still remains to be found.

Chicxulub impact crater and the K/T mass extinction revisited.

http://geoweb.princeton.edu/people/keller/smit.pdf However, the "evidence" that purports to show that the Chicxulub crater is 300.000 years older than the K/T boundary, is exclusively based on resedimented coarse grained deposits in the vicinity of the crater, i.e. the Gulf of Mexico, that have been influenced by tsunami waves, mass-wasting and slumping and earthquakes triggered by the impact itself. Therefore, in all these places there is a sedimentological explanation for the doubling, tripling of layers with ejecta and iridium, creating the illusion of multiple impacts. The grains could be washed in from inside the crater, from the rim or the direct surroundings of the crater, and may therefore be much older or younger than the crater itself. In other words, it is impossible to tell whether the foraminifera in that core-segments are contemporaneous, older or considerably younger than the crater. So what and where is the best evidence that ties the Chicxulub impact to the K/T boundary extinctions? In my opinion thoseare the impact layers laid down in quiet coalswamps in the US and Canadian western interior. Those layers are found over a wide area ranging from Alberta; Hell Creek, Montana; Dogie Creek, Wyoming; and Raton Basin, Colorado-New Mexico. Glenn Izett, Bruce Bohor and colleagues have shown that in those areas there is a single claylayer, composed of two parts. The lower sublayer is filled with spherules that are identical to the glassy spherules from around the Gulf of Mexico. Ar/Ar age dating, chemical and isotopic composition of the glass show that, barring a miracle, those spherules are derived from the Chicxulub impact. The upper sublayer is invariably enriched in iridium (according to Gerta Keller the fingerprint of the "unknown" K/T boundary impact) and shocked minerals. Additionally, the upper sublayer contains shocked zircon crystals that tie the sublayer to the Chicxulub target (panafrican) rocks. If Gerta Keller would be correct, than the lower and upper sublayers would be separated in time by about 300kyr. In reality, the two sublayers are not even separated by a single season of falling leaves, in all the localities menti

Late Cenozoic Uplift in Southern Asia and the American West: Rationale for General Circulation Modeling Experiments

http://onlinelibrary.wiley.com/doi/10.1029/JD094iD15p18379/abstract Geologic evidence suggests significant increases in uplift rates and absolute elevation in several areas during the late Cenozoic, especially in the last 10 m.y. Regions of major uplift include the Tibetan Plateau and Himalayan Mountains of southern Asia; and the Sierra Nevada, Colorado Plateau, Basin and Range, Rocky Mountains, and High Plains of the American west. Uplift occurred at a scale large enough to affect regional and global climate in a number of ways, several of which we evaluate by General Circulation Model experiments in accompanying papers. Evidence used to infer paleouplift: 1) Faulting and volcanism 2) Vegetation and pollen 3) River downcutting Evidence of uplift in SA: 1) Himalayas and Tibet Evidence of uplift in American West: 1) Sierra Nevada 2) Colorado plateau 3) Rocky Mtns 4) High plains Summary: Althought the current state of knowledge of paleoelevation histories is still fragmentary and unsatisfactory, there is a consenesus favoring major net uplift during the late Cenozoic in several regions, includin southern AAsia and the American west. The series of GCM sensitivity tests can be related to actual geologic uplift histories.

"The Birth of Complex Cells" Christian de Duve,

http://science-learning2011.wikispaces.com/file/view/The%20birth%20of%20complex%20cells-sciam-1996.pdf/237730527/The%20birth%20of%20complex%20cells-sciam-1996.pdf Prokaryotes do not have nucleus (first living organism) Spawned a wide variety of species and invaded all habitats. --> and now eukaryotes. Eukaryotes: nucleus, 10,000x bigger, highly structure genetic info, skeletal elements within cytoplasm, specialized organelles (ex peroxisomes, mitochondria, plastids) Eukaryotes branched away from prokaryotes ~before 3 billion yrs ago -Lynn Margulis championed bacterial origins of mitochondria and plastids via endosymbiont adoption. A host cell basically probably swallowed a mitochondria/plastid etc. Evolution of Eukaryote: loss of cell wall, convolution, inward folding Proposition of why pro-->eu: 1) ancestral cell lived in surroundings that provided it with food 2) ancestral cell had to digest its food 3) organism lost its ability to manufacture a cell wall -results in growth in size, enzymes and convoluted folds to digest food -peroxisomes precursor to mitochondria -plastids precursor to chloroplasts -reinforcement by fibrous and tubular structures *result = primitive phagocyte How did anaerobic phagocytes survive during all the time it took for the ancestors of mitochondria to evolve? - peroxisomes Migration of genes from endosymbionts to the nucleus The slow conversion, over as long as one billion years or more, of a prokaryotic ancestor into a large phagocytic microbe possessing most attributes of modern eukaryotic cells

"Extraterrestial Cause for the Cretaceous-Tertiary Extinction"

http://users.unimi.it/paleomag/geo2/Alvarez+1980.pdf Summary. Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus in- dicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Den- mark, and New Zealand show iridium increases of about 30, 160, and 20 times, re- spectively, above the background level at precisely the time of the Cretaceous-Ter- tiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would sup- press photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothe- sis has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 2 4 kilometers.

"An Extraterrestial Impact" Alvarez and Asaro

http://www.colorado.edu/geography/courses/geog_1011_s05/geog_1011_r1.pdf 10 km asteroid moving at > 10 km/s Evidence supporting asteroid impact: 1) presence of mineral spherules 2) shocked quartz - multiple intersecting planar lamellar bands of deformation symptomatic of hypervelocity shock. Found only at known impact craters or nuclear test sites. 3) similar composition of rocks at KT (ex. low os 147 levels) Evidence against volcanic: 1)gloabl distribution of iridium 2) shocked quartz production 3) basaltic spherules ******* Proponents of volcanic argument claim extinction took a long time and wasn't a sudden event - found iridium enrichment spread over 500,000 years Also flipping of earth's magnetic field suggests core and mantle activity/disturbances in line with rising mantle plumes leading to volcanic activity

"Late Cenozoic Uplift of Mountain Ranges and Global Climate Change: Chicken or Egg?"

http://www.colorado.edu/geolsci/faculty/molnarpdf/1990Nature.Molnar&England.pdf Pleistocene glaciation is recognized as a consequence of variations in Earth's orbit superimposed on a long-term global cooling throughout the Cenozoic era. There are three mechanisms by which large mid-lat terrains' uplift could effect a global cooling: 1) increased elevations at temperate latitudes could extend duration of winter --> increased snow cover --> increased albedo. 2) Increase in elevation of large regions should profoundly affect the circulation of the atmosphere. 3) Chemical weathering enhanced by higher-latitude conditions would absorb more carbon dioxide and decrease greenhouse effect. Article argues that most of the evidence used to infer late Cenozoic uplift could, in large part, be a consequence of the very climate changes that this supposed uplift is thought to have caused.

"The Oldest Hominid Yet"

http://www.nature.com/nature/journal/v371/n6495/pdf/371280a0.pdf Tim White and coworkers found teeth fossils ~4.5 million years old that lie close to the divergence between apes and humans. (A. Ramidus) Australopithecus africanus, A. afarensis (Lucy) A ramidus, pushed back knowledge of human lineage by more than 0.5 million years. A Afarensis 3.4~3.8 M yrs old A Ramidus recovered from Middle Awash, which lies either side of the Awash river in Ethiopia. Use a sample (MA92-37) of the underlying GATC vitric tuff's contemporary feldspar crystals to give an age ~4.4 Myr. Woodland hypothesis. Actually more like a chimpanzee than Afarensis. A more radical taxonomic solution would have been to erect a new genus for the Aramis remains - but only remains from other parts of the skeleton will confirm whether that would be justified. Finds at Aramis are a vindication of proposals, based on protein morphology that modern humans hare a close and relatively recent ancestry with the African apes.

"Strength of the San Andreas"

http://www.nature.com/nature/journal/v405/n6782/full/405031a0.html questions regarding the feasibility of shorter-term predictions, and whether the occurrence of one earthquake increases the probability of an earthquake on another fault, remain unanswered. Scholz argues that the San Andreas fault (Fig. 1) is relatively 'strong'. Over the past three decades, hundreds of laboratory experiments have indicated remarkably similar friction coefficients of between 0.6 and 1.0 for a wide range of rocks3. Extrapolating these observations to natural faults implies that extremely high stresses should be required to cause fault motion at great depth, assuming normal (approximately hydrostatic) pore pressures. Pore pressure is the pressure of fluids, principally water, within the cracks and pores of a rock at depth. In the context of Scholz's argument, a strong San Andreas means that, to a depth of about 10-15 km (where large earthquakes nucleate), the frictional resistance to sliding along the fault is high. This is essentially consistent with the stresses predicted from laboratory friction experiments with hydrostatic pore pressures. Scholz argues that the San Andreas (and by inference the other major faults which bound lithospheric plates) has essentially the same frictional strength as the faulted crust within the plates — in other words, that the hundreds of kilometres of offset that have occurred along the fault have been accomplished without significant weakening of the fault with respect to the surrounding brittle crust. HOWEVER Taken together, the heat flow and in situ stress orientation data indicated to many researchers that the San Andreas, and perhaps other plate-boundary faults, was a profoundly weak fault in an otherwise strong crust. The absolute strength of the San Andreas is likely to remain controversial until we obtain measurements, from within the fault itself, of the stress levels and physical conditions under which earthquakes occur.

"The Big Picture" Carroll, 2001, Nature, v. 409, p. 669.

http://www.nature.com/nature/journal/v409/n6821/full/409669a0.html microevolution: events at or below the species level macroevolution: above the species level, including the formation of species * Is microevolution sufficient to account for macroevolution? Macroevolution: paleontologist: phyletic evolution (origins and extinctions of species) biologistL morphological evolution: independent of timescale or phylogenetic context Explanations for the Cambrian patterns of phyletic evolution tend to focus on extrinsic environmental and ecological factors as catalysts for the rapid diversification of clades The crucial question is whether there is any evidence that distinct macroevolutionary mechanisms affect morphological or phyletic evolution. The subdivision of evolution into two scales no longer reflects our understanding of the unity and diversity of evolutionary mechanisms. macro- = micro- = evolution

"From Landscapes into Geological History" Philip A. Allen

http://www.nature.com/nature/journal/v451/n7176/full/nature06586.html ***Geological deformation and climate might have coupled relationship*** Erosional and depositional landscapes are linked by the sediment-routing system. Observations over a wide range of timescales might show how these landscapes are translated into the narrative of geological history. In the deep geological past, there were periods of pronounced convergence and collision of tectonic plates, when they organized themselves into great supercontinents before splitting and dispersing. One such period of assembly about 680-530 million years ago produced the great supercontinent known as Gondwanaland. The topography caused by the formation of mountains perturbs atmospheric circulation and steers the jet stream, thereby directly influencing regional and local climatic patterns, such as the distribution of precipitation. Strong gradients in precipitation patterns in turn dictate erosional behaviour as well as ecosystem type. This first-order feedback between tectonics and climate, seen as major spatial variations in precipitation between the wet windward side and the dry lee, is uncontroversial. What is more contentious is that the impact of tiny raindrops, through erosion, might cause the localization of the mighty forces of tectonic deformation; that is, erosion over a tectonically deforming crust (Fig. 2) encourages a flux of rock towards the site of surface erosion. Consequently, it has been proposed that heavy monsoon rains, and the resulting high erosion rates, might cause dormant faults to become active, that earthquakes might be concentrated near areas of high erosion, and that growing kilometre-scale folds in the fronts of mountain belts might amplify rapidly once they have broken through Earth's surface and experience erosion. Surprisingly, rates of tectonic deformation near the surface of Earth, and earthquake risk, might therefore be influenced by climate. At a basic level we know that high rates of deformation must be balanced by erosion, otherwise mountain ranges would continue to grow until they reached a height limit governed only by rock strength, or deep holes would appear in the core of mountain ranges in the absence of tectonic deformation. Upland catchments release sediment into adjacent river systems or alluvial fans like a well-directed fire-hose, but the preservation of sediment in these systems depends on whether space is available for it to accumulate over long timescales. In areas such as the Basin and Range province of the southwestern United States, where the crust is extending by slip along steep normal faults, it is believed that sediment fans, which accumulate against the uplifting mountain ranges, reflect the rate at which the faults slip by repeated earthquakes. Where the faults slip rapidly, the sediment fans are thought to have steep surface slopes and to show rapid down-system changes in particle size

"Unlocking the Mysteries of the Ice Ages"

http://www.nature.com/nature/journal/v451/n7176/full/nature06589.html -What caused the Northern Hemisphere's ice sheets to come and go? Milutin Milankovic acute, who turned Croll's argument on its head in the 1930s. He argued that glaciation occurs when insolation intensity is weak at high northern latitudes during summer. This happens when both Earth's spin axis is less tilted with respect to the orbital plane and aphelion coincides with summer (not winter) in the Northern Hemisphere. According to Milankovic acute, when there is less insolation during the summer, snow and ice persist through the year, gradually accumulating into an ice sheet. In 1976, James Hays, John Imbrie and Nicholas Shackleton1 unearthed strong evidence in support of the orbital hypothesis of glaciation. Applying the newly developed geomagnetic timescale to a deep-sea sediment core, they showed that long-term variations in oxygen isotope ratios, as recorded in fossils of foraminifera, were concentrated at the frequencies predicted by the orbital hypothesis. The ratio of oxygen-18 to oxygen-16 (delta18O) in the ocean was known to increase with glaciation, because oxygen-16 evaporates preferentially and is concentrated in ice sheets. Hays et al.1 showed that delta18O varied with cycles of 41,000 years, the period associated with changes in the tilt of Earth's spin axis (or obliquity), and around 21,000 years, the period associated with the location of aphelion with respect to the seasons (also known as climatic precession or the precession of the equinoxes). One resolution to the puzzle of the missing precession variance harks back to Adhémar's proposal: summers with the greatest insolation intensity are also about a week shorter than the average duration of summer, because Earth orbits more quickly when it is close to the Sun. Peter Huybers3 proposed that the amount of melting an ice sheet undergoes is better gauged by integrating the total insolation over summer (with summer defined as the period when insolation intensity exceeds a melting threshold), as opposed to using either the peak or the mean intensity of summer insolation. Huybers and Eli Tziperman4 recently demonstrated that an ice-sheet model can generate 40,000-year glacial cycles when two conditions are met: the zone where the ice sheet is ablated must be north of about 60° N, where changes in obliquity have a greater effect on insolation, and the summer melt season must be long enough for changes in its duration to balance changes in insolation intensity. Clark and Pollard proposed that a glacial substrate of easily deformable sedimentary rocks allowed basal sliding to increase and therefore resulted in a continental ice sheet that was thinner overall. They proposed that the gradual erosion of this upper sedimentary layer by ice sheets led to the transition to the larger, less mobile ice sheets of the late Pleistocene that varied at the slower 100,000-year periodicity. Another explanation for the lack of a precession signal in records of ice volume was proposed by Maureen Raymo, Lorraine Lisiecki and Kerim Nisancioglu6. They put forward a model in which Northern Hemisphere ice sheets wax and wane at precession periods, driven by the strongly nonlinear response of ice ablation to summer insolation intensity. It is widely accepted that variations in Earth's orbit affect glaciation, but a better and more detailed understanding of this process is needed.

"Finding Design in Nature" Cardinal Schonborn,

http://www.nytimes.com/2005/07/07/opinion/07schonborn.html?_r=0 Christians: while leaving to science many details about the history of life on earth, proclaims that by the light of reason the human intellect can readily and clearly discern purpose and design in the natural world. Evolution in the sane of common ancestry might be true [to them]. but evolution in the neo-Darwinian sense - an unguided, unplanned process of random variation and natural selection - is not. Pope John Paul II: "It is clear that the truth of faith about creation is radically opposed to the theories of materialistic philosophy. These view the cosmos as the result of an evolution of matter reducible to pure chance and necessity." "the letter cannot be read as a blanket approbation of all theories of evolution, including those of a neo-Darwinian provenance which explicitly deny to divine providence any truly causal role in the development of life in the universe."

"Shocked Quartz in ther Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution, 1987, Bohor, et al.

http://www.sciencemag.org/content/236/4802/705.abstract Shocked quartz grains displaying planar features were isolated from Cretaceous- Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis. use precession diffraction techniques crystallographic orientations omega{1013} seen often in the shocked quartz

"Australopithecus ramidus, a New Species of Early Hominid from Aramis, Ethiopia, 1994, Nature, v. 371, p. 306-311

http://www2.ku.edu/~lba/courses/articles/White%20ramadis94.pdf Seventeen hominoid fossils recovered from Pliocene strata at Aramis, Middle Awash, Ethipia make up a series compresing dental, cranial, and postcranial specimens dated to around 4.4 million years ago. When compared with Australopithecus afarensis and with modern and fossil apes the Aramis fossil homonids are recognized as a new species of Australopithecus - A. Ramidus sp. nov. The antiquity and primitive morphology of A. ramidus suggests that it represents along-sought potential root species for the Hominidae. Distinguished from Afarensis (and other known hominids) by: larger upper and lower canines relative to postcanine teeth, no anterior fovea, thinner canine and molar enamel, more dominant buccal cusp etc. Distinguished from apes: higher crown shoulders, crowns less projecting, foramen magnum anteriorly placed relative to auditory meatus etc. Retains first deciduous molar- similar to chimpanzee (small). Canine enamel thickness similar to chimpanzee too. pre-5 Myr record of homind is sparse A-Ramidus is the most is the most apelike hominid ancestor known and its remains suggest that modern apes are probably derived in many characters relative to the last common ancestor of apes and humans. More work at Aramis should further elucidate the sexual dimorphism, locomotion, diet, and habitat of this species.

"The rise of atmospheric oxygen" free access, Kump, Nature 451, 277-278 (17 January 2008)

http://www3.geosc.psu.edu/~jlm80/Geosc497/Kump2008RiseofOxFeature.pdf Clues from ancient rocks are helping to produce a coherent picture of how Earth's atmosphere changed from one that was almost devoid of oxygen to one that is on-fifth oxygen. 1) Earth's earliest atmosphere was devoid of oxygen 2) today's atm is 21% oxygen * the shift from anoxic to oxic ~ 2.5-2 billion yrs ago -lack of 'red beds" in sedimentary rocks in older stratigraphic units -"smoking gun" for rise of oxygen = rocks older than 2.45 bil yrs contain a large degree of mass-independent fractionation (MIF). Rocks younger than 2.32 show none. -to preserve MIF sig: a) very low oxygen b) sufficient sulfur c) substantial cct of reducing gases (methane) Why oxygen levels rose when they did... -establishment of large, thick and stable continental land masses MIF disappears when oxygen levels reach 0.001% of present atmospheric level