what are the various theories that can prove where water came from?

Question

how did the earth come to have a surface of about 78% water?

i know a couple of theories on it, but i want to know all of them.

what have you read (where, a link please?) about how earth became the water planet?

Answer 1

Water is central to our planet. Every living thing requires it. Everything that has ever lived required it. Without liquid water, the Earth is a barren, lifeless rock. Fortunately, the Earth has abundant water.

We can fairly well tell how they probably occurred. Most scientists believe that volcanic eruptions helped form the Earth’s bodies of water. Volcanoes shoot out water vapor when they erupt. Volcanoes would have been blowing this water vapor into the atmosphere for millions of years before the oceans formed. For a significant chunk of time, however, the earth was a giant ball of molten lava. This kept all of the water in vapor form. When the Earth began to cool, the water condensed and formed the oceans.

Scientists don’t agree so easily on when the first large bodies of water appeared. Certainly there was water on Earth before the oceans appeared, but none of it was liquid. There are two schools of thought on when the oceans formed. The first and more popular school believes that the oceans appeared around 500 million years after the formation of the Earth. There is, however, a smaller school of scientists who believe the Earth may have had oceans from as little as 100 million years after its formation. They say that the presence of zircons, a type of crystal, as old as 4.4 billion years suggest there may have been water at this time.

Answer 2

The question really isn't where did all the water come from, but more WHY earth is the only planet in the solar system that has a watery surface.

Anyway, I dug around, looking for references to turekian, Ringwood, Holland and origin of the earth and finally came up with one that gives a fairly good discussion (see ref below).

Most of the links I obtained were for articles that are not accessible without subscription.

Your best bet if you are interested in the subject is to visit your local university library and spend a lot of time.

Basically, the thinking is either that the water was accreted with the other materials or added after the earth cooled enough to retain water. As with most things of this nature, reality is probably a mix of the two, and it becomes a question of which is more important. There are problems with both sides.

Clearly, either mode of origin should also have added water to our sister planets Mars and Venus, and to explain the uniqueness of the watery earth, one also needs to explain why these other planets are not also watery.

There will never be a proof, by the way, just evidence that is consistent or inconsistent with the various models.

Answer 3

There are 2 prominent theories I remember from my planetary geology class. They are not separate from one another but work in conjunction with one another. Outgassing and condensation from the cooling Earth and comet impacts. Comets are mostly ice so when they hit Earth they melted or vapourized to add water to the planet.