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GEOG 205 (26)

February 4th

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McGill University
GEOG 205
Gail Chmura

February 4 , 2013: Geologic Time and the Evidence of the Land  geologic time divided into eras, periods and epochs  use sediments/fossils from rocks to determine age  rocks that look the same but in different area of the world are from same era  only have relative time ages, not absolute numbers  existence/presence of certain organisms aren’t the same in all location on earth - not simultaneous, so how to determine?  we are living in the Cenozoic era o specifically the Quaternary period  began 2.6 million years ago  Pleistocene Epoch began 2.588 million years ago  Holocene Epoch began 0.0117 million years ago  us  remember what a crevasse & moraine are****  ice ages = Pleistocene epoch  have remnants of the ice ages  scientists questioned erratic boulders that lead to paradigm shifts o boulders lifted & deposited due to flood  fit nicely in religious culture (Noah’s flood); also followed idea that earth formed by series of catastrophic events o drift theory  erratic boulders frozen in icebergs & drifted to location during flood o glacial ice (Louis Agassiz)  suggested erratic boulders moved by glacial ice; not adopted outside of Switzerland; explained how additional features could be formed by glaciers  ice edge creates terminal moraine  very useful for determining furthest extent of a particular ice advance  drumlins are tear shaped hills that tell direction of glacial advance  striations (scratches) on rocks also show direction of glacial movements (rocks carried under ice make the marks)  eskers (curving ridge of sand & gravel) show water flow but not direction  glacial till (not good for agriculture)  loess soils  winds swept away  ice sheet is larger than a glacier  gravel luds deposited during cold periods = greater erosion of watersheds o various levels = terraces o warm period = interglacials or interstadials had more vegetation, less erosion o ages based on assumed rates of erosion  glacial vs. stadial  4 fold theory of glaciations o 4 stages each associated with ice sheet development & advance and based
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