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The Pleistocene

The Pleistocene. Causes of Glaciation. 1) Why is there ice anywhere on Earth? 2) If there is ice, what makes it contract and expand?. Before 3.5 Ma. After 3.5 Ma. Milankovitch Cycles. Milutin Milankovitch (1879-1958).

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The Pleistocene

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  1. The Pleistocene

  2. Causes of Glaciation • 1) Why is there ice anywhere on Earth? • 2) If there is ice, what makes it contract and expand?

  3. Before3.5 Ma After 3.5 Ma

  4. Milankovitch Cycles Milutin Milankovitch (1879-1958)

  5. Precession of the equinoxes. The direction of the long axis of the ellipse itself rotates slowly. It has the effect that at certain times aphelion will occur during the northern hemisphere winter and at other times aphelion will occur during the northern hemisphere summer. The period of precession of the Earth's orbit is between 19,000 and 21,000 years.

  6. Changes in obliquity. The Earth's axis of rotation is tilted relative to the plane in which the Earth orbits around the sun (the plane of the ecliptic). Currently the tilt (obliquity) is 23.5o, but it varies between 21.5o and 24.5o with a period of about 41,000 years.

  7. Changes in eccentricity of the orbit.The Earth's orbit around the sun is elliptical with the sun at one focus of the ellipse. The eccentricity changes cyclically with a period of about 96,000 years.

  8. The End-Pleistocene Mass-Extinction of Large Mammals

  9. Pleistocene of Alaska

  10. The La Brea Tar Pits

  11. The La Brea Tar Pits

  12. The La Brea Tar Pits Columbian mammoth American mastodon

  13. The La Brea Tar Pits Dire wolf

  14. The Pleistocene Mass-Extinction More than 200 genera of very large herbivores (2 tons or more) go extinct, including 95 % in North America The disappearing mammals in North America included: Mammoths Dire wolves Mastodons Giant jaguar Horses Saber-tooth cat Tapirs Ground sloths Peccaries Four-horned antelopes Giant beaver Camels

  15. The Pleistocene Mass-Extinction The following disappeared from America, Europe and Australia: All herbivores > 1000 kg 75% of herbivores 100-1000 kg 41% of herbivores 5-100 kg < 2% of herbivores < 5kg

  16. The Pleistocene Mass-Extinction It occurred at different times on different land masses: Time of start of major extinction episodes(years before present) Africa and S.E. Asia 50,000 Australia 50,000 North Eurasia 13,000 North America 11,000 South America 10,000 West Indies 4,000 New Zealand 900 Madagascar 800

  17. Possible Causes of the Pleistocene Mass Extinction 1) Climate 2) Human Hunting

  18. Clovis Projectile Points

  19. UF14616Mammuthus columbi (Columbian mammoth)thoracic vertebra spine with cut marksGilchrist County, Florida

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