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EPS 102 lecture 19

EPS 102 lecture 19 - E PS 102 lecture 19 Thu rsday April 2n...

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EPS 102 lecture 19 Thursday April 2 nd , 2009 Record we have of the Earth and it’s influence on Paleoclimate: The Geological record gives us information, and the basic result that it gives us is that the world has seen very different climates than what we have seen as humans. The Earth has seen more environments in the past than we have seen in terms of human history. Global warming refers to warming in some selective areas. It’s not about whether global warming is good or bad, but in terms of humans, any impact or change can be stressful. If sea level rises, some people may not have to worry about it but in the Bay Area the predictions are as many as a few feet in the rise of the sea level of the bay itself. A million years to a geologist is a short period , but since the KT impact (demise of the dinosaurs) 65 million years ago we have a rich geologic record. The basic theme is: 65 million years ago the global climate was warmer ; there is evidence and problems with this evidence. Around 40 million years ago, the Earth started cooling and from one point of view, we are actually in a cooler than typical period. Global warming is actually “good,” because people think it will bring us back into a more natural or normal period. One can even say that the general cooling trend occurred differently in the Northern and Southern Hemisphere. Evidence includes the marine records from which we get good global coverage and resolution. Data that was collected through the ocean drilling program : we drill out cores of the muds that are on the bottom of the ocean and these muds tell us a story of the climate and ocean salinity/temperature state back in time. A ship goes out and collects cores; the core is not absolutely continuous instead it is choppy. People are looking for fossils and microfossils such as foraminifera and diatoms= bottom of the macroscopic food chain that have shells made of Silica and Carbonates in many cases. This history is explored due to the oil industry. We also know that the species and subspecies formed depend on where you are in the ocean: polar vs. equatorial regions. One of the big steps forward is to go beyond just looking at the shapes of these organisms but looking at geochemical analyses:
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Oxygen isotopes measure the different abundances of oxygen in benthic microorganisms. If you can look at the oxygen in the calcium carbonate: oxygen 16, 17, and 18. Heavy oxygen refers to oxygen 18 versus the lighter oxygen which refers to oxygen 16. If the abundances of heavy and lighter oxygen (these are stable isotopes, meaning they are not radioactive or radiogenic) might vary as a function of temperature, and we can measure that in the fossil record, we can get a record of paleooceanographic and paleoclimatic conditions. The vast predominant isotope of oxygen in our atmosphere is oxygen 16. Smaller percents are oxygen 18 and 17. Oxygen 18 : Oxygen 16 ratios (heavy: light) is studied extensively. Fractionation refers to
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