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Ice Age

World History Ice Age Unit

Lahryn Spencer

on 17 September 2012

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Transcript of Ice Age

photo credit Nasa / Goddard Space Flight Center / Reto Stöckli Since the last 1 million years, our species and our human forebears experienced a dozen or so major glaciations of the northern hemisphere, with the greatest ever occurring around 650,000 years ago. The Ice Age During this period of extreme ice buildup,
the ice advanced deep into the Midwest,
from its center around Hudson Bay in Canada,
and deep into Germany, from its center on
the Scandinavian Shield. So much ice collected in these two major regions and
several lesser ones that the sea level
dropped by some 400 feet and the overall
global temperature was lowered
by around 5°C (about 9°F). Mammoth, mastodon, wooly rhinoceros,
giant bison, camels, horses, and
many large predators (cats, wolves, bears)
roamed the grasslands well south of the rim of the miles-high
ice, both in North America and in Europe. Small bands of humans made a living
by hunting and gathering in Africa, and
perhaps elsewhere. The glaciation that occurred 650,000 years ago
lasted some 50,000 years. After this great glaciation, a succession of
smaller glaciations has followed,
each separated by about 100,000 years
from its predecessor, The last of the ice ages in human experience
(often referred to as the Ice Age)
reached its maximum roughly 20,000 years ago,
and then gave way to warming. Sea level rose in two major steps,
one centered near 14,000 years and the other near
11,500 years.
However, between these two periods
of rapid melting there was a pause in
melting and sea level rise, known
as the "Younger Dryas" period. During the Younger Dryas the climate system
went back into almost fully
glacial conditions, after having offered balmy
conditions for more than 1000 years. Ice Ages and Ice Cores
The carbon dioxide content of the atmosphere
for the last 4 glacial cycles is known
from drilling into the ice in Antarctica,
where ancient air has been trapped
and now can be extracted. These results show that carbon dioxide
follows the change
in sea level rather closely: when
carbon dioxide increases,
sea level rises and vice versa. A similar relationship is seen for methane. Most likely, changes in trace gases help drive
sea level up and down,
Full transcript