LATE PLEISTOCENE EXTINCTIONS :
CAUSES AND CONSEQUENCES
Summarize key events
Much of this occurred during a time of climatic fluctuations – the Ice Ages. or
THE PLEISTOCENE EPOCH
The Ice Ages began 1.8 million years ago, and we are probably still in them.
Characterized by alternating periods of cold, dry (glacials) and warm, wet (interglacials).
Geologic record indicates that there were four major glacial intervals during the past 1.8
The last major advance of ice sheets began about 100,000 years ago and peaked
around 18,000 years ago.
It then ended rather suddenly around 12-10,000 years ago.
record of glaciation has been reconstructed using a variety of kinds of fossil data,
including oxygen isotope ratios in microfossils of shelled marine organisms, shifting
of marine organisms with known environmental requirements, and shifting
plant distributions as revealed by pollen analyses.
Three large glacial centers developed in the Northern Hemisphere during glacial
North America, Greenland, and Scandinavia.
Around 18,000 years ago,
glaciers extended as far south as New Jersey, as evidenced by the sedimentary record.
Glaciers leave clues of their passing such as scratches/gouges on rocks and mixed, poorly
sorted deposits of rocks, pebbles, sand and mud that they plow ahead of themselves as
During glacials, the plants and animals would retreat southwards and then
expand northwards again during interglacials, and this is documented in the fossil record.
Although we have some understanding of what controls the timing of the glacials and
interglacials, it is not at all clear what initiated the pattern.
As was pointed out last
quarter, the cycling of glacial and interglacial phases seems tied to changes in the nature
of the earth's orbit around the sun. But these changes have been going on forever, and so
why do we only see ice ages at certain times in earth history (late Ordovician,
Carboniferous, and Pleistocene)?
The initiation of ice ages seems tied to the presence of