Earth was able to support life only after it had cooled enough for the crust to solidify and water to condense and accumulate. The first living things in the water were probably primitive heterotrophic prokaryotes (bacteria) that obtained their energy and nutrients from an oxygen-free environment by fermentation. Such organisms are still found today in anoxic environments such as volcanic vents deep in the oceans.


Simple Cells - Prokaryotes

The oldest fossils known are prokaryotes. They are bacteria and cyanobacteria (blue-green algae) without a nuclear membrane protect the cell's limited genetic material (DNA). These simple organisms reproduce by cell division forming exact copies of themselves, a process that allows them to multiply rapidly but to evolve slowly. Therefore prokaryotes have been until today the most successful and most numerous life form on Earth.

Light and Life transform
the atmosphere

Single-celled blue-green algae called cyanobacteria evolved and were capable of photosynthesis. They were able to make their own food using the energy of the sun and CO₂ from the atmosphere. As a byproduct they released oxygen. Increasing numbers of such single-celled algae living in the seas eventually released enough oxygen into the atmosphere to transform the Earth’s environment.