Did Comets Create the Earth's Oceans? - Universe Today
Where did the world's oceans come from? Some scientists believe all that water was originally locked into rocks, and slowly leaked out over millions of years. Others believe it was delivered from space by comets crashing into our planet. The European Space Agency's Rosetta spacecraft might help find the answer. When it reaches Comet 67P/Churyumov-Gerasimenko, Rosetta will send down a small lander, Ptolemy, that will measure the chemical signature of the comet's water, and see if that matches our water.