4-2 Ma

  • 4-3 Ma: Pliocene warming interval and higher CO2 concentrations, humid conditions in East Africa, and weak zonal and meridional sea surface temperature (SST) gradients.

  • 3.6-3.4 Ma: Lake phase in NE Africa.

  • Onset of major Northern Hemisphere glaciation between 3.2-2.6 Ma and development of arid conditions in East Africa.

  • 3-2 Ma: Development of strong sea surface temperature gradients in equatorial Atlantic and Indian Oceans.

  • More seasonally-contrasted, cooler, and drier—and perhaps more variable—climate in North Africa.

  • ~2.8 Ma: Increase in eolian dust fluxes around North Africa.

  • After 2.8 Ma: Expanded amplitudes of North African wet-dry cycles.

  • 2.7-2.5 Ma: Deep lake phase in NE Africa.

  • By 1.8 ma: Disappearance of persistent El-Niño like conditions in tropical Pacific.

  • 2.8 Ma: Growth of polar ice sheets and lowered sealevel, onset of glacial/interglacial cycles.


  • Trend for Australopithecus to have larger and taller cheek teeth, reduction of canines, and to maintain a high level of sexual dimorphism.

  • ~ 3-2.4 Ma: Split between australopithecines and Homo.

  • ~2.7 Ma: Evolution of Paranthropus.

  • ~1.8 Ma: Evolution of more carnivorous H. erectus.

  • Australopithecus species disappeared from East African record.

  • 2.58-2.52 Ma: Earliest stone tools.

  • After 2.3 Ma: Stone tools increasingly common.

  • Australopithecines initially associated with fauna that indicates woodland with some grassland or more bushland habitats; first appearance of Equus in Africa and connections with Eurasia grassland expansion, which is coupled with increased body size in Homo.

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