The lack of a rock record makes it difficult to study the early earth. Due to the movements of the earth’s lithosphere the rocks have been recycled destroying any evidence that might have existed. The early atmosphere probably contained a plentiful amount of carbon dioxide for the greenhouse effect. The greenhouse effect was important as the sun’s energy output was much less at this time. The earth’s interior was warmer at this time and probably a great deal of volcanic activity was taking place. Theses eruptions are believed to have put water vapor into the atmosphere to form clouds blocking even more radiation from the sun cooling the earth thus starting the first rains.
Degassing of earth’s interior furnished the water for ocean development. The oceans then stored heat and evaporation took place to supply the atmosphere with more water vapor for cloud formation and the cycle kept repeating itself.
There was no free oxygen in the atmosphere at this time so ozone could not be formed to filter the ultraviolet radiation which is harmful to living things. The climate was warm, humid and rainy when early life forms first appeared about 3.8 billion years ago. These primitive life forms probably added oxygen to the atmosphere which helped to start the ozone layer.
Around 1.4 billion years ago, enter the eukaryotic cell. This is the greatest single leap in evolution as sexual reproduction allowed for a wider variety of organism to evolve. Increased oxygen production was also taking place.
