1. The Pleistocene

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

15. Before 3.5 Ma After 3.5 Ma

17. Milankovitch Cycles Milutin Milankovitch (1879-1958)

20. 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.

21. 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 23.5 o, but it varies between 21.5 o and 24.5 o with a period of about 41,000 years.

22. 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.

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

28. Pleistocene of Alaska

30. The La Brea Tar Pits

31. The La Brea Tar Pits

32. The La Brea Tar Pits Columbian mammoth American mastodon

33. The La Brea Tar Pits Dire wolf

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

39. The following disappeared from America, Europe and Australia: All herbivores> 1000 kg 75% of herbivores100-1000 kg 41% of herbivores5-100 kg < 2% of herbivores< 5kg The Pleistocene Mass-Extinction

43. It occurred at different times on different land masses: Time of start of major extinction episodes (years before present) Africa and S.E. Asia50,000 Australia50,000 North Eurasia13,000 North America11,000 South America10,000 West Indies4,000 New Zealand900 Madagascar800 The Pleistocene Mass-Extinction

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

48. Clovis Projectile Points

50. UF14616 Mammuthus columbi (Columbian mammoth) thoracic vertebra spine with cut marks Gilchrist County, Florida

51. Asian (L) African (R)