11/8/20171Paleo Climate & Human Origins1Topics 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 bipedality211/8/20172How do we know the conditions of natural selection in the past? 3Initial point:“Climate” is not “Weather”411/8/20173Setting the Stage: Global temperature drop at the end of the Miocene EpochBipedal apes5The 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).This amount of energyis distributed over this amount of spaceat the equatorfar from the equator611/8/20174Variation in Solar Radiation received by the Earth:…the seasons.7Milankovitch Cycles1) 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)811/8/20175Milankovitch Cycles2) Eccentricity of the orbit or ellipse (96 ky cycle). Weakest theoretically but dominates the periodicity of glaciations after 1 million ago.9MilankovitchCycles3) Precession of the equinoxes (19/23 ky cycle)Affects interaction of the first two cycles.Results in greater seasonal contrasts1011/8/20176The combined effects of tilt, eccentricity, and precessionresult in a very accurate “prediction” of insolation (radiation received by the planet) which is then mirrored in our best paleoclimate proxies11Milankovitch 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.1211/8/20177ALA#9b: What type of mating system do chimpanzees practice?a. Monogamy b. Polygynyc. Polygynandryd. Polyandrye. None of the above13Plate Tectonics: continental drift1411/8/2017815Geosphere 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.1611/8/20179Hydrosphere positive feedback toward glaciation: Drake Passage Still ClosedConnection of South America to Antarctica before 25 mya: • Antarctica exposed to warm waters circulating down from the Equator to the polar region.17Hydrosphere positive feedback toward glaciation: Opening the Drake Passage18Separation 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.11/8/201710ALA#9c Which of the following contexts are goodfor fossil preservation? List the letters that apply.a-Weatheringb-Consumption by carnivoresc-Rapid burial by fine grained sedimentsd-Rapid burial by coarse grained sedimentse-Acidic soilf-Low energy conditionsSetting the Stage: Global temperature drop at the end of the Miocene Epoch2011/8/20171121How do we know what we know about prehistoric global climate?The Oxygen Isotope Cycle2122Calcareous shells of Foraminifera (planktonic & benthic) capture oxygen isotopes and thus become proxies for sea water temperature & volume2211/8/20171223Deep sea sediment cores: marine sludge is good for science2324If marine sludge is good for science …so is freezing your ass off.2411/8/201713OceanGlacier18O16O18O18O16O16O16ODuring Glacials, light evaporated water gets “stuck” in glaciers, so ice becomes “light” with 16OSea water becomes “heavy” with 18O“Delta-18O”or δ18O ratio recorded in sediments at bottom of the sea25262611/8/20171427• We are currently in Oxygen Isotope Stage 1 (OIS 1).• Odd numbers = Interglacials (warm, less ice)• Even numbers = Glacials (cold, more ice)27Take-Home Messages for Paleoclimatic Reconstruction1. 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!2811/8/20171529Could carbon dioxide-induced Global Warming simply cancel out the upcoming Ice
View Full Document
Unlocking...