Where did earth’s water come from?

Where did earth's water come from? - Researchers examining hydrogen isotope ratios in meteorites appear to have thrown a spanner in the works of the latest models of how elements such as hydrogen and nitrogen reached the early Earth. The finding throws up questions about where all the Earth's water came from and how life on Earth began. Reference: C M O’D Alexander et al, Science, 2012: (10.1126/science.1223474)