ENVIRONMENT

The Coldest Millennia

~26,500 to 19,000 years ago

Palaeolithic · Upper Palaeolithic · Last glacial · Last Glacial Maximum

At the Last Glacial Maximum, from about 26,500 to 19,000 years ago, ice sheets kilometres thick lay over Canada and Scandinavia, and the sea stood some 120 to 140 metres lower, welding Asia to America and Australia to New Guinea. Every human being alive then lived through it: populations drew back into refuges, and the habitable world was for a while both larger, where the shelves lay dry, and harsher nearly everywhere.

Why it matters

This is the crucible in which the peopled world was cast. The lowered sea opened the very bridges and coasts by which the Americas were entered; the cold packed peoples into refuges whose separations are still legible in genomes; and when the ice let go, a fifth of the dry land went under, in sight of people who remembered it and moved inland.

Dating & uncertainty

Defined from thousands of dated glacial deposits: nearly all ice sheets stood at their maximum from 26,500 to about 19,000 years ago, with deglaciation in the north beginning at 19,000 to 20,000. The 21,000 anchor marks the conventional centre of the plateau, not an event.

Sources

1. Clark et al. (2009), Science · The Last Glacial Maximumdoi:10.1126/science.1172873
2. Clark (2014), PNAS · Closing the sea level budget at the Last Glacial Maximumdoi:10.1073/pnas.1418970111
3. Gowan et al. (2021), Nature Communications · A new global ice sheet reconstruction for the past 80 000 yearsdoi:10.1038/s41467-021-21469-w

Our species’ history as one day

22:24:001 h 36 min before midnight

if the 315,000 years of Homo sapiens were compressed into a single day