the pleistocene. causes of glaciation 1) why is there ice anywhere on earth? 2) if there is ice,...
TRANSCRIPT
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 MaAfter 3.5 Ma
Milankovitch Cycles
Milutin Milankovitch(1879-1958)
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.
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.
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.
The End-Pleistocene Mass-Extinction of Large
Mammals
Pleistocene of Alaska
The La BreaTar Pits
The La BreaTar Pits
The La BreaTar Pits
Columbian mammoth
American mastodon
The La BreaTar Pits
Dire wolf
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
More than 200 genera of very large herbivores (2 tons or more)
go extinct, including 95 % in North America
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
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
The Pleistocene Mass-Extinction
Possible Causes of the Pleistocene Mass Extinction
1) Climate
2) Human Hunting
Clovis Projectile Points
UF14616Mammuthus columbi (Columbian mammoth)thoracic vertebra spine with cut marksGilchrist County, Florida
Asian (L) African (R)
