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How did water first come to earth? Water was part of the earth when it was first formed. Most scientists agree that almost all the water on earth was a part of the earth when it first formed. However, a very small amount of the water on earth today probably came from comets. Comets are like large dirty snowballs traveling through space. If a very large comet comes into the earth's atmosphere, some of the water may get to earth. Scientists don't always agree on many things and some scientists don't agree about comets bringing water to earth. Some scientists today would say that most of the earth's water came from comets and some would say that none of the earth's water comes from comets. There are scientists whose job is to study this topic to get information to tell who is right. For now the answer most people would agree with is that most of the earth's water was on the earth when it was formed but a very small amount was brought here by comets.