Tuesday, April 28, 2020

Events in Evolution


Events in Evolution
In its 4.6 billion years circling the sun, the Earth has harbored an increasing diversity of life forms:
  • for the last 3.6 billion years, simple cells (prokaryotes);
  • for the last 3.4 billion years, cyanobacteria performing photosynthesis;
  • for the last 2 billion years, complex cells (eukaryotes);
  • for the last 1 billion years, multicellular life;
  • for the last 600 million years, simple animals;
  • for the last 550 million years, bilaterians, animals with a front and a back; 

  • for the last 500 million years, fish and proto-amphibians; 

  • for the last 475 million years, land plants;
  • for the last 400 million years, insects and seeds; 

  • for the last 360 million years, amphibians;
     
  • for the last 300 million years, reptiles; 

  • for the last 200 million years, mammals; 
     
  • for the last 150 million years, birds;
  • for the last 130 million years, flowers; 

  • for the last 60 million years, the primates, 

  • for the last 20 million years, the family Hominidae (great apes);

  • for the last 2.5 million years, the genus Homo (human predecessors);

  • for the last 200,000 years, anatomically modern humans.
Periodic extinctions have temporarily reduced diversity, eliminating:
  • 2.4 billion years ago, many obligate anaerobes, in the oxygen catastrophe; 

  • 252 million years ago, the trilobites, in the Permian–Triassic extinction event; 

  • 66 million years ago, the pterosaurs and nonavian dinosaurs, in the Cretaceous–Paleogene extinction event.
Dates are approximate.



No comments:

Post a Comment