C4 grasses take over the world
A new way of doing photosynthesis lets grasses conquer the tropics, and whole faunas change their teeth to match.
- When
- —
- Duration
- 2.7 million years
- Known to
- ± 1 million years
- Era
- Miocene, Cenozoic
C4 photosynthesis concentrates carbon dioxide around the fixing enzyme, which makes it far more efficient than ordinary C3 photosynthesis when carbon dioxide is low, temperatures are high and water is short. C4 grasses exist earlier but between about 8 and 3 million years ago they expand explosively across Africa, Asia and the Americas, creating true tropical grassland and savanna. Carbon isotopes in fossil teeth record the shift directly: herbivores across four continents switch from browsing to grazing within a few million years.