It is not very likely that the total amount of water at Earth’s surface has changed significantly over geologic time. Based on the ages of meteorites, Earth is thought to be 4.6 billion years old.
The oldest rocks known are 3.9 billion to 4.0 billion years old, and these rocks, though altered by post-depositional processes, show signs of having been deposited in an environment containing water.
There are three stages in the evolution of the present atmosphere:
- The first stage is marked by the loss of primordial atmosphere.
- In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere.
- Finally, the composition of the atmosphere was modified by the living world. Through the process of photosynthesis.
The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds.
The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen.
The process through which the gases were outpoured from the interior is called degassing.
The earth’s oceans were formed within 500 million years from the formation of the earth. This tells us that the oceans are as old as 4,000 million years.
Sometime around 3,800 million years ago, life began to evolve.
However, around 2,500-3,000 million years before the present, the process of photosynthesis got evolved. Life was confined to the oceans for a long time.
Oceans began to have the contribution of oxygen through the process of photosynthesis.
