U of M ANTH 1001 - Lecture 17 11-7-17 Paleo-climate (15 pages)

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Lecture 17 11-7-17 Paleo-climate



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Lecture 17 11-7-17 Paleo-climate

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Pages:
15
School:
University of Minnesota- Twin Cities
Course:
Anth 1001 - Human Evolution
Human Evolution Documents
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11 8 2017 Paleo Climate Human Origins 1 Topics for Today Methods of paleoclimatic reconstruction Climate vs weather Milankovitch Cycles Historical contingency of Earth s climate Which came first big brains or bipedality Biomechanics of bipedality 2 1 11 8 2017 How do we know the conditions of natural selection in the past 3 Initial point Climate is not Weather 4 2 11 8 2017 Setting the Stage Global temperature drop at the end of the Miocene Epoch Bipedal apes 5 The primary influence on Earth s climate the Sun Solar energy is unevenly distributed over the surface of the earth because the earth is round a globe far from the equator This amount of energy is distributed over this amount of space 6 at the equator 3 11 8 2017 Variation in Solar Radiation received by the Earth the seasons 7 Milankovitch Cycles 1 Obliquity of spin axis 41 ky cycle greater the tilt the greater the seasonality results in more or less solar radiation between polar and equatorial regions 8 4 11 8 2017 Milankovitch Cycles 2 Eccentricity of the orbit or ellipse 96 ky cycle Weakest theoretically but dominates the periodicity of glaciations after 1 million ago 9 Milankovitch Cycles 3 Precession of the equinoxes 19 23 ky cycle Affects interaction of the first two cycles Results in greater seasonal contrasts 10 5 11 8 2017 The combined effects of tilt eccentricity and precession result in a very accurate prediction of insolation radiation received by the planet which is then mirrored 11 in our best paleoclimate proxies Milankovitch Forcing IS necessary but NOT sufficient to cause an Ice Age it is the feedbacks between the Geosphere Hydrosphere Atmosphere which push the planet over the edge in either direction 12 6 11 8 2017 ALA 9b What type of mating system do chimpanzees practice a Monogamy b Polygyny c Polygynandry d Polyandry e None of the above 13 Plate Tectonics continental drift 14 7 11 8 2017 15 Geosphere positive feedback toward glaciation Snow and ice reflect sunlight and thus heat away from planet albedo Albedo prevents snow melting which leaves snow to make more albedo Orogeny mountain building due to plate tectonics allows for more places with high albedo 16 8 11 8 2017 Hydrosphere positive feedback toward glaciation Drake Passage Still Closed Connection of South America to Antarctica before 25 mya Antarctica exposed to warm waters circulating down from the Equator to the polar region 17 Hydrosphere positive feedback toward glaciation Opening the Drake Passage Separation of South America Antarctica at 25 mya Allows the creation of Antarctic Circumpolar Current by Earth s rotation Cuts Antarctica off from warm southward flowing currents leaving it to freeze Historical contingency of Earth s climate 18 9 11 8 2017 ALA 9c Which of the following contexts are good for fossil preservation List the letters that apply a Weathering b Consumption by carnivores c Rapid burial by fine grained sediments d Rapid burial by coarse grained sediments e Acidic soil f Low energy conditions Setting the Stage Global temperature drop at the end of the Miocene Epoch 20 10 11 8 2017 How do we know what we know about prehistoric global climate The Oxygen Isotope Cycle 21 21 Calcareous shells of Foraminifera planktonic benthic capture oxygen isotopes and thus become proxies for sea water temperature volume 22 22 11 11 8 2017 Deep sea sediment cores marine sludge is good for science If marine sludge is good for science so is freezing your ass off 23 23 24 24 12 11 8 2017 During Glacials light evaporated water gets stuck in glaciers so ice becomes light with 16O 18O 16O 18O Glacier 16O 16 18 16 O O O Sea water becomes heavy with 18O Oce an Delta 18O or 18O ratio recorded in sediments at bottom of the sea 26 25 26 13 11 8 2017 We are currently in Oxygen Isotope Stage 1 OIS 1 Odd numbers Interglacials warm less ice Even numbers Glacials cold more ice 27 27 Take Home Messages for Paleoclimatic Reconstruction 1 Earth s climate is influenced by large scale cycles dictated by orbital parameters 2 The way the large scale cycles affect the Earth are altered by feedback systems between the Geosphere and the Hydrosphere 3 Climate is historically contingent small details in one variable can change the whole system 28 14 11 8 2017 Could carbon dioxideinduced Global Warming simply cancel out the upcoming Ice Age 29 15


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