Science Forums 2

[LJP07]

I always thought it came from huge meteorite impacts, and as far as I understand it's from two sources Primary Water and Water from Comets.

Two of the elements found in the Universe commonly are Oxygen and hydrogen. They are chemically quite reactive, and so they both combined with various other elements to form chemical compounds. One of these compounds is water, and water quickly became an important part of the earth's surficial layer ( Surficial Layer is the layer which is relating to something happening or being on earth), along with many other familiar chemicals like Silica. Water flowed and flowed which eventually became the oceans as we know it. However, in Earths First Billion years and over the past 4.5 billion years, the main source of water was from comets.

We know that comets consist chiefly of chemical compounds that are either gases or liquids at earth-surface conditions: methane is one common component of comets and water is another. Although I am not an expert in this field, that's how I currently understand it.