Radio carbon dating stone
Although the glaciers had retreated, the climate was still quite cold.Paleo Indian had immigrated across the Bering Sea by the land bridge of the Aleutian Island chain (known as Beringia) from Siberia into North America and followed a corridor south between the retreating ice sheets, perhaps to hunt wooly mammoth.A more recent theory propose prehistoric Solutreans of Ice Age France also sailed west to America across the Atlantic Ocean along the south ridge of the polar ice cap more than 18,000 years ago.What was the climate like when people first came here?Northern Illinois has an unusual climate history due to its latitude and geology.It is thought they brought Clovis point technology (earlier, similar points were found in France) and genetic diversity (such as red hair and large noses) to Native Americans.The exact date humans came to North America will not be found soon, but the Hebior and Schaefer Wisconsin mammoth sites about 350 miles northeast of our recovery site were recently carbon-dated to 15,000 to 16,500 years ago and contained artifacts that were basically cutting and skinning tools.Both white spruce (Picea glauca) and black spruce (Picea mariana) were present, as was larch (Larix laricina).
This question has been hotly debated for over a century, especially now with the recent interest in the last Ice Age.According to established theory, sometime during the Pleistocene, around 13,000 years ago, the last great eastern ice sheet, the Laurentian, reached down only to Wisconsin and was already receding.After the Wisconsin glacier retreated from the Chicago region, it still occupied and dammed the northern end of the Lake Michigan basin, forming glacial Lake Chicago.This lake, which covered most of present-day Chicago, was higher than modern Lake Michigan.[By analyzing pollen and fossilized vegetation in this ancient Ice Age lakebed scientists have determined that at the closing of the last Ice Age, the southwestern Chicago region and the northern half of Illinois was like no other place on earth: covered the landscape.
The Chicago region in particular was once under the southern edge of the Wisconsinan ice sheet.
When this massive ice sheet started to retreat 18,000 years ago, it depressed the land and created a widen basin: Much of the city of Chicago lies on beach and lake sediments deposited by Lake Michigan and its predecessor glacial Lake Chicago.