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5_1 Miocene_Pleistocene Environments_Lecture Script.pdf

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Simon Fraser University
ARCH 131
Dennis Sandgathe

UNIT 5CLIMATE AND THE CONTEXT OF HUMAN EVOLUTION Slide 1 Title slide Slide 2 Researchers studying trends in human evolution have looked for parallels between patterns in Hominid evolution and climatic changes The thinking is that perhaps major trends or changes in our hominin ancestors things like Encephalization and bipedalism were responses to environmental change While direct relationships between climate and specific evolutionary developments may be over simplistic there is little doubt that changes in climate and environment played important roles in human biological and cultural evolution Slide 3 As we have seen in earlier lectures the Cenozoic Era 65 million years ago to present is when most of the evolution of primates occurred This period is marked by a relatively constant decrease in average global temperatures an increased variability in temperature between the equator and the poles and an increase in seasonalitySlide 4 rse This graph illustrates the trend in global temperatures over the couof the Cenozoic Starting about 50 million years ago at the start of the Eocene epoch and ending around 35 million years ago at the end of the Eocene here was a major relatively continuous drop in global temperatures Slide 5 One of the main causes of this temperature decrease was changes in the configuration of the continents and the flow of ocean waters between them This has a major effect on Earths temperature circulation For much of the Earths history the continents were bunched together into a more compact mass which allowed ocean waters to more easily move over more of the Earths surface In particular this allowed waters that were heated at the equator to more easily and readily move north and south spreading warm waters over more of the globe and keeping global temperatures much more homogenous Prior to 50 million years ago the average global temperatures were much higher than today and the difference between temperatures at the equator and at the poles was far less extreme Over the last 50 million years a number of changes in the position of the continents has changed this and reduced the movement of warmed ocean waters into the polar regions Slide 6 Two of the most important changes at the beginning of this period were1 the closing of the Tethys Seaway between the African and Eurasian continents2 and the separation of the S American continent from Antarctica Slide 7 The Tethys Seaway was a narrow course of midlatitude waters hat joined the Atlantic and Pacific oceans between Africa and Eurasia tIt was a major body of water situated near to the equator where it could be heated and then flow freely both east and west It was a major source of heated ocean waters when it existed Slide 8 e African and Arabian Between 50 million and 35 million years ago thplates began colliding with the Eurasian plate partially closing the Tethys Seaway slowing down and eventually cutting off eastwest flow
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