The first four-legged animals, or tetrapods, evolve from intermediate species such as Tiktaalik, probably in shallow freshwater habitats.
Mar 16, 900
The first multicellular life develops around this time.
May 1, 1500
Eukaryotic cell organisms develop
The oldest fossils of single-celled organisms date from this time.
Beginning of photosynthesis by blue-green algae which releases oxygen molecules into the atmosphere and steadily works to strengthen the ozone layer and change the Earth's chemically reducing atmosphere into a chemically oxidizing one
The Earth's crust solidifies--formation of the oldest rocks found on Earth
Formation of the approximately homogeneous solid Earth by planetesimal accretion