CLIMATE

The Ice Ages

~2.6 million to 11,700 years ago

Phanerozoic · Cenozoic · Quaternary · Pleistocene · Gelasian

Ice sheets grew over North America and northern Europe and melted away again, dozens of times, following slow wobbles in the Earth's orbit that change how much sunlight reaches the north in summer. Sea level went up and down with them by more than a hundred metres. The rhythm itself changed: every 41,000 years until about 900,000 years ago, every 100,000 years after that, and no change in the orbit explains the switch.

Why it matters

Our species evolved inside this beat, and every human society before the last ten thousand years lived through some part of it. The stable warmth we call normal is one interglacial among dozens, and it is the only one anybody has ever farmed in.

Dating & uncertainty

The pacing is well measured and its cause is not fully explained. Ice sheets advanced and retreated every 41,000 years until about 900,000 years ago, then every 100,000 years, a switch that no change in the orbit accounts for.

Sources

1. Hays et al. (1976), Science · Variations in the Earth's orbit: pacemaker of the ice ages
2. Lisiecki & Raymo (2005), Paleoceanography · A Pliocene-Pleistocene stack of 57 globally distributed benthic oxygen isotope records
3. Ford & Chalk (2020), Oceanography · The mid-Pleistocene enigma

Earth history as one day

23:59:1049.1 s before midnight

if Earth’s 4.54 billion years were compressed into a single day