The Mid-Pleistocene Transition begins
Glacial cycles start stretching from 41,000 years to 100,000, and the ice grows far thicker.
- When
- —
- Duration
- 476 thousand years
- Known to
- ± 50 thousand years
- Era
- Early Pleistocene, Quaternary
Beginning around 1.25 million years ago and completing after 800,000, the climate system changes its response to orbital forcing: cycles lengthen to roughly 100,000 years, become strongly asymmetric — slow build-up, rapid collapse — and reach much colder glacial maxima with far larger ice sheets. The orbital forcing itself does not change, which is the puzzle. Leading explanations combine slowly declining carbon dioxide with the glacial stripping of regolith down to bedrock, which lets ice sheets grip and grow thicker.