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.