The Precambrian is usually broken into three sections:
The Azoic (or Hadean) Era, 4.5-3.5 billion years ago, during which the Earth cooled after forming (Azoic means "no life");
The Archaeozoic (or Archaean) Era, 3.5-2.8 billion years ago, for which there is a minute evidence of prokaryotic (bacterial) life, similar to that on the Mars Meterorite,
- The Proterozoic Era, 2.8 billion-600 million years ago, whose fossils consist mainly of stromatolites deposited by cyanobacteria and blue-green algae. Eukaryotes first appeared during the Proterozoic and eventually the Ediacarans 1.4 billion years ago. Long, long before Pangaea, the supercontinent Rodinia formed and broke up during the Proterozoic. The "Snowball Earth" theory proposes that the Proterozoic ended with a severe ice age in which glaciers covered the entire surface of the Earth for millions of years.