The time at which the total volume of ice began to shrink is hard to determine exactly but was probably close to 18k B.P. This date is often regarded as that of the final maximum of the Wisconsin glaciation.
Conditions south of the ice sheets at 18k BP: There is no question, however, that there were forests, tundra, and grasslands of sufficient extent to nourish a tremendous assortment of larg mammals. The most famous of these were the elephantlike mastodons and mammoths.. .
A multitude of other large mammals loved not far south of the ice sheets. As wide a variety of habitats must have existen then as now, each with its quota of species. Taking them all together, the diversity is impressive...
Herivores that are now extinct included Mexican horse, a small horse that was probably common in the Great Plains, and western camel, which is believed to have grazed in lage herds. These two seices were abundant and, judging from their extant relatives, were animals of grassland rather than of tundra. There was also wooland muskox, which was tallen and thinner than the extant tundra muskox and had the bases of the horn sheaths fused to form a single dome of horn; shrub-ox, with a skull apparently adapted to smash agains that of rivals in heat-to-head combat, as happens with modern bighron sheep; and stag-moose, which resembled modern moose except for its elaborately forked antlers...
The carnivores that are now extinct were far more spectacular. They included the dire wolf, which was similar to the modern timber wolf but much more powerful ...; the famous sabertooth, which was about the size of a modern African lion and had enormous saber teeth, apparently adapted for stabbing; the somewhat smaller scimitar cat, whose comparatively sort scimitarlike canines had shapr, saw-toothed edges fore and aft; the American lion and the American cheetah, which were not unlike their modern African counterparts. The giant short-faced bear may well have been the most awe-nspiring carnivore of them all; it was as tall as a moose, and compared with modern bears of the genus Ursus, rather short bodied, which suggests that it was a swift runner. Its short, broad muzzle must have enabled it to grip and hang on to its quarry. . .
First, the year 10k BP marks the "official" end of the Pleistocene epoch. . . That is to say, it has been defined, by professional geologists (specifically, by a subcommission of the International Quaternary Union, known as INQUA), as the date of the Pleistocene/Holocene transition. The year 10k B.P. is therefore epoch making by definition.
Second, the year 10k B.P., or at any rate a fairly short interval centered on that year,
mark the end of an epoch in the ordinary sense. As noted in chapter 9, the terrestrial biosphere underwent some rapid and important changes at approximately 10k B.P., which are believed to signal a sudden, major climatic change. Three of these abrupt occurrences, as they could be called, deserve particular mention.
The first of them has to do with the amount of carbon dioxide in the atmosphere, which has fluctuated widely over the millennia. The atmospheric concentration of carbon dioxide in times past can be discovered by taking cores of ice from existing ice sheets. The ice consists of datable annual layers, each containing small air bubbles representative of the contemporary atmosphere; the carbon dioxide content of the air in the bubbles can be measured. Ice cores collected at Camp Century in northern Greenland and at Byrd Station in Antartica have been analyzedin this way, and it turns out that carbon dioxide concentration increased steadily, from a value of about 210 parts per million at roughtly 17k B.P. to about 280 parts per million at roughly 10k B.P.(note the unavoidable imprecision). The value remained close to 280 parts per million thereafter, until the human population and industrial explosion of own time caused the value to start climbing again. Pielou 1991,227-
At least ninety percent of the present-day prairies was under water--submerged by an ice front lake--or under stagnant ice for at least a few decades following the disappearance of active ice.
The land that first became available for terrestrial vegetation was therefore certainly wet.. . Precipitation must also have been greater then than it is now; . . . Pielou 1991,232