User talk:Spiggot/Origin of water on earth

Nicely written but does not include many current theories. Even those who believe that much of the earth's water comes from either original material or from its aggregation on dust particles are willing to allow that up to half of earth's water arrived with the impact of comets. The discovery of a comet in 1999 by LINEAR lent weight to this theory as the discovered comet has a deuterium content more closely resembling that of the earth's oceans. Therefore, this comet would appear to have originated much closer than the oort cloud or kuiper belt, which would have been the case for many other comets (and asteroids) early in the earth's lifetime.