How life began on earth and in the oceans?

Regarding to scientists, the earth was formed approximately 4.54 billion years ago. It was unhabitable because of its temperature and the lack of water and atmosphere. It seems that the first volcanoes on earth released gases, and water vapor. Due to these different releases, what scientists called “primitive atmosphere” was created.

About the oceans, they seemed to be formed 3.8 billion years ago. At this time, there was still no form of life on earth, and science has still no answer on how life appeared in oceans. But concerning the formation of oceans, they apparently were created by the high temperature in the primitive atmosphere. Indeed, rocks, minerals and volcanoes that contained molecules of water released steam. This steam became clouds, then rain. After millions and millions of years, this accumulated water formed oceans. It is also interesting to know that comets had also a role in the water present on earth. Comets are mostly made of ice and other gas, so when they crashed into the earth, the ice melted into liquid water.

Anyway, at the beginning oceans were not suitable for life, and the atmosphere either. It needed billions of years to make a right balance between the gases on earth, the temperature, and the composition of the oceans to impact the atmosphere and make it possible to any form of life to exist.

The most accepted theory says that the first forms of life appeared around 3.7 billion years ago, in the form of single-celled microorganisms. These microbes are resistant of high and low temperature, with or without oxygen and even in sea with high level of salt. This theory is built on the study of stromatolites, rocks that are made by layers of sediments and mud over time. The discovery of cyanobacteria in these stromatolites was relevant because they were the first organisms able to produce oxygen via photosynthesis. Nowadays they are still present in extreme environment and the stromatolites are still forming in marine and non-marine environments.