Earliest Known life forms
From ~2 billion to 500 million years ago
- Early life forms - little evidence
- no hard parts (no teeth, bones, shells or claws)
- Earliest Rocks - limited life forms, single-celled organisms
- 2 billion years ago some rocks show evidence of blue-green algae
- Multi-celled creatures appear 1 billion years ago
- Oxygenated atmosphere developed
- Marine animals with shells widespread by 600 million years ago