The Last Glacial Maximum
During the Last Glacial Maximum (LGM) (26.5–19.5 TYA) vast ice sheets blanketed much of North America, Europe, and Asia. The greatest extent of glaciation was 22 TYA, though there were regional differences in glacier advance and retreat. At maximum glacial extent, some 30% of Earth’s surface was iced over. Glaciers formed on African mountains. Continental glaciers pushed to the 40th parallel in some places. The north 40th parallel runs near Denver, Philadelphia, Madrid, Ankara, and Beijing.
Because of reduced ocean evaporation, the climate was not only cold but also drier. Forests were fewer, steppe and deserts more extensive.
Massive ice sheets locked water away. Sea levels dropped 130 meters. Continental shelves were exposed, joining land masses together and creating extensive coastal plains.
The world was inhospitable, with frequent storms and an atmosphere laden with dust: 20–25 times dustier than today. This owed to reduced vegetation, stronger global winds, and aridity: less precipitation washing dust out of the sky.
Conversely, interglacials are conducive to life on land, which expanded accordingly. Many remote Pacific islands, including Australia, were settled by humans during the warmer, wetter period preceding the LGM.
Rainfall in Australia declined 90% during the LGM. The Amazon rainforest was bifurcated, with a swath of savanna between them. The tropical rainforests of southeast Asia were similarly affected.