The Sahara pump
The desert turns green and back again every twenty thousand years, opening and closing a corridor.
- When
- —
- Duration
- 1.8 million years
- Known to
- ± 100 thousand years
- Era
- Early Pleistocene, Quaternary
Precession-driven shifts in the African monsoon repeatedly push rainfall north, converting the Sahara from desert into grassland dotted with lakes and rivers, then back again, on a roughly 20,000-year beat. Each green phase opens a corridor between sub-Saharan Africa and the Mediterranean that animals and hominins can cross; each arid phase closes it and isolates the populations on either side. The Sahara pump is one of the principal mechanisms controlling when anything could leave Africa by land.