Last Glacial North America

The last glacial period reached a peak between 25 000 and 18 000 years ago according to calibrated radiocarbon dating. Evidence for what the world was like at this time is relatively abundant and well preserved, certainly in comparison with earlier glacial periods whose record has been greatly disturbed by later ice action and other geomorphic processes. Around 21 000 Cal. yr bp, temperatures on land had fallen by as much as 20°C (Wright et al., 1993), although ocean temperatures changed much less. The reconstruction by the CLIMAP project members (1976) indicated that for tropical parts of the ocean, sea-surface temperatures for the last glacial maximum were within 2°C of the present. More recent work has suggested that the true temperature fall may have been nearer to 5 degree Celsius, how­ever, under the full glacial climate, the ice sheets over four kilometer thick lay over North America and northern Europe, and smaller ice caps found in the southern Andes, the Alps, and parts of the East Asia. Most of northern Asia was too dry for ice sheets to form, and Siberia consequently experienced intense periglacial activity. Much of today's deep permafrost layer is, in fact, a relict from the last glacial period.

The build-up and decay of ice sheets locked up and then released water from the hydrological cycle, causing ocean vol­ume to fluctuate and sea levels to rise and fall (Tooley and Shennan, 1987). Global sea levels were lowered on average by more than 100 m at glacial maxima, creating new continental land masses in areas such as Southeast Asia. Land bridges were exposed, so that it became possible to walk from East Asia to Alaska or from Britain to the European mainland. This undoubtedly aided the spread of fauna and of early human populations into new or marginal areas. It was the era of the woolly mammoth, the American sabre-tooth tiger and of the ice-age hunters who portrayed their prey so vividly on the cave walls at Lascaux in southwest France.

Questionnaire:

• Explain about the Last glacial in North America and Europe.