Rosetta Probe Shows "Comets 'Did Not Bring Water to Earth'" -- So Where Did It Come From?

The abundance of water on Earth is one of the most important parameters that make our planet finely tuned for life. But how did Earth come to be so rich in this vital resource? That is a question that has vexed scientists for some time. Smithsonian Magazine explains the problem:

Water molecules were surely part of the dusty swirl that coalesced into the Sun and its planets beginning about nine billion years after the Big Bang. But Earth's early history, including epochs with high ambient temp...