Additional Facts 8. Twenty thousand years ago, a glacial ice sheet over one mile thick covered New York state.
That thick sheets of ice covered much of northern North America can be seen in deposits of terminal moraines of the ice sheet's southern extent for location and for ice sheet thickness by measuring the amout of "glacial rebound" wherein the land is still rising from the unloading effect of the weight of the previously thick glacial ice. So much ice covered the continents that global sea level had fallen nearly 400 feet. Sea level reached near its current position about 7,000 years ago. This tremendous melting occurred over a 10,000 year period with no manmade climate influence so the recent advances and retreats of the glaciers are well within Earth's natural climate oscillations. (See figure below)