Asteroids as a Source for Water on Earth

Numerical studies were made in order to investigate the evolution of terrestrial planets and asteroids in the early solar system. Here we give some results of Petit et ah, 2000 [260]. 

The deuterium to protium (D/H) ratio of the deep mantle may be a remnant of the hydrogen isotopic composition of Earth forming planetesimals. The mass of asteroids and comets incident on Earth since the time of its accretion is estimated to be 4 X 10 -2 X 10 kg. The combined use of water D/H ratios, the lunar cratering record, and terrestrial mantle siderophiles would favor a rather low mass fraction of comets among impacting bodies ( 0.01). Asteroids, comets, and the early Earth contributed to 0-0.5, 0-0.1, and 0.5-0.9 of Earth s water inventory, respectively (Dauphas, Robert, and Marty, 2000 [94]). 

The role of comets and primitive asteroids in supplying water and prebiotic organics to early Earth was reviewed by Mumma, 2008 [240]. 

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