The Laurentide Ice Sheet — the massive continental glacier that covered most of Canada and reached into the northern United States — was at or near its greatest extent.

Ice was miles thick over what is now Montreal, Chicago, and Boston.

The Great Lakes did not exist as lakes — the basins they occupy were filled with glacial ice.

Sea levels worldwide were substantially lower than today, because so much of the world’s water was locked in ice.

The Bering land bridge was exposed — a broad, grassy plain connecting northeastern Asia to western Alaska, through which animals and people could move without crossing open water.

The question of whether people were moving through that land bridge at 23,000 years ago is exactly what the White Sands dates complicate.