Geology Week 11 notes
Geology Week 11 notes GEOL1005
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This 6 page Class Notes was uploaded by Kate Notetaker on Thursday March 31, 2016. The Class Notes belongs to GEOL1005 at George Washington University taught by Catherine A. Forster in Winter 2016. Since its upload, it has received 52 views. For similar materials see Historical Geology in Geology at George Washington University.
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Date Created: 03/31/16
March 29, 2016 Isotopes o Normal Hydrogen represents around 99.98% of all Hydrogen on Earth and is stable o Deuterium represents 0.0026 – 0.0184% of all Hydrogen atoms on Earth and is stable Half life o Each half life is the amount of time it takes for half of the amount of a radioactive element to decay into a stable element o Uranium has a very long half life Gamma-Knife radiosurgery for brain tumors o We know the rate at which the isotopes are decaying o Decay is clock-like Radioactive isotopes are useful for applications that demand a clock or clock-like behavior o Stable isotopes are good for freezing environmental records in time Reconstructing the past climate using stable isotopes o Water cycle sorts isotopically light and heavy oxygen Evaporation, precipitation, etc. Process of sorting this oxygen is fractionation o 1O is going to be evaporated more easily than 18O because it is 13% lighter 18 Water vapor that is depleted of O with respect to the ocean o The 18O that does make it into the clouds is preferentially removed by precipitation as rain Heavier, tends to be the water molecule that falls out as rain Rain water enriched in 1O makes it back into the ocean 18 o Clouds 16at have mad18it far inland have vapor depleted of O O rich and O depleted precipitation in stored in glacial ice Trap that water with a certain isotopic position for a period of time o When it is warmer there is enough energy to evaporate both 1O is and 1O in abundance More 18O stored in ice How can we reconstruct past temperatures using this information? o What kind of data do we need to collect? o Antarctica The coldest place on earth is also a desert Gets 22 millimeters of snow per year Very cold year round As long as Antarctica has been there and covered in ice, then it has deposited year after year 22 millimeters of snow per year Snow becomes compacted and forms glacial ice Drills through the ice until it hits bed rock Gets past record of the ice isotopic information from this ice Heavily compacted ice low in the core has annual cycles from which isotopes can be analyzed Figure out which intervals correspond to a year Annual cycle enriched in 1O is a warmer year 18 Annual cycle depleted of O is a colder year We can measure the CO direc2ly o Can go into the sections of the ice poles o Can measure the CO from2the bubbles in the ice Why are we concerned with CO if we2re worried about reconstructing temperature? o Greenhouse effect CO a2d other gases in the atmosphere trap heat, keeping the Earth warm Some is trapped inside and other heat escapes We can extend the record further into the past by using the stable isotopes present in fossils of marine micro-organisms o Benthic Foraminifera Bottom dwelling Protists with CaCO s3ells o Planktonic Foraminifera Free floating Protists with CaCO s3ells o As long as we know what geological time period these came from o Bivalve and Brachiopod shells are also made of CaCO 3 o CaCO shells of fossil marine micro-organisms allow us to collect 3 proxy temperature and CO reco2ds hundreds of millions of years in the past o Marine invertebrate fossils enriched in 18O is a warmer year Depleted is a colder year Many other proxy systems for collecting paleoclimate data o Annual growth lines in corals Width of those bands Better for the modern record o Tree rings o Looking at fossil leaves Stomata that performs gas exchange functions We can observe patterns of stomatal density vs atmospheric CO 2 Birds have a really efficient respiratory system o Conveyor belt Only occurring when they breathe in and out o Air sacs Pneumatic Foraminae Go into the bone o Benson et al. found a weak but significant correlation between postcranial skeletal pneumaticity and body size in theropods Concluded that the early evolution of postcranial skeletal pneumatisation in theropods was likely driven by gravitational constraints Rate of respiratory evolution in fossil Archosaurs tracks changes in atmospheric oxygen content and temperature o Especially for periods of environmental instability Archosaur lineages that didn’t change their respiratory systems died in major extinctions o Use this and apply it to the environmental changes that we’re seeing today March 31 Land End of the Cretaceous o Dinosaurs o Birds also dinosaurs but a specific branch o Mammals o Angiosperms o Turtles, crocs, lizards, etc. First part of the Cenozoic Paleogene o Dinosaurs go extinct o Birds make it through but suffer a lot of losses Able to radiate and evolve throughout o Mammals suffer losses but make it through Allows mammals to take over because dinosaurs are extinct o Angiosperms suffer losses but make it through o Turtles, crocs, lizards, etc. make it through with no problem at all Other than land End of the Cretaceous o Plesiosaurs o Pterosaurs o Ammonites o Planktonic forams Forams that are at the top because they are photosynthesizers o Benthic forams Live at the bottom of the ocean Don’t necessarily need the light Paleogene o Plesiosaurs go extinct o Pterosaurs go extinct o Ammonites are now known to make it though the extinction Make it through but go extinct eventually o Planktonic forams 95% extinction Just a few survive o Benthic forams Mildly hit Don’t undergo too much extinction All the herbivores and carnivores go extinct o It’s the omnivores that survive o Things that survive have a giant radiation Mammals get back on top o Birds also dominate in the Paleogene as well Climatic cooling at the end of the Cretaceous o Oxygen isotopes show us that things are cooling off at the poles o Polar plants are now changing to more temperate species Global drop in sea level end of the Cretaceous o If sea level drops, we have exposure of some of the continental shelf o Less space for marine organisms Emplacement of another volcanic province end of the Cretaceous o Beginning of the Deccan Traps India moving north at this point o As India moves North, it goes over a hot spot Mantle upwelling of hot magma hot spot o 512000 km of volume of these Deccan Traps o In place in three different phases 1 phase Late Cretaceous nd 2 phase Cretaceous – Paleogene boundary Most of it happens after the boundary Marine o Deep sea cores o Marine sediment on land that crosses the Cretaceous –Paleogene boundary o Planktonic forams Suffering extinctions prior to the boundary In other areas they only suffer extinctions only at the boundary o Ammonites Can see extinctions only at the boundary In other areas there are extinctions leading up to the boundary o Most sections that you look at in the marine Show sudden extinctions right at the boundary Catastrophic extinction event Land o Very few sections of terrestrial sediments that extend from the Late Cretaceous, through the boundary, and to the Paleogene o Hell Creek formation Cretaceous Boundary that goes to the Paleogene Dinosaurs No extinction before boundary Instantaneous extinction Birds Nice and healthy up to the boundary Extinction at the boundary Not a slow extinction but rapid instead 1980 Walter Alvarez o Studying a sequence around Gubbio, Italy o Sampling for iridium Very common in extraterrestrial comets Rains down on Earth from particles from space o At the boundary, there is a huge amount of iridium Huge spike right at the boundary Realized that the only way to have that much iridium must have been a large meteor impact Starts finding this spike globally o Impact hypothesis Was the large extinction due to a large impact? o Shocked quartz Quartz grains that have undergone high pressures Very rare Only commonly found at impact sites and volcanic sites o Tectites (microspherules) Glass o Fern spike Just above the iridium layer Spores from ferns Chicxulub o 112 miles in diameter o Melt sheet o 10 km diameter o K-Pg o Hit in 300 m of water o Tsunamis filled with iridium o Subsurface imaging shows the extent and configuration Huge crater o Greater the angle of impact, effects how much material is thrown into the air 192,000 gigatons of TNT o Billions of tons of rock and dust Upper atmosphere o Block out light o Drop temperatures Impact o Reduced temperatures and light levels o High extinction rates o Fern spikes o Omnivores tended to survive o Smaller animals who could eat anything survived o Crocodiles and snakes didn’t have to eat often That’s why they survived so well After the Extinction o Mammals had diversified and increased in size o Birds radiated
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