Water at the start, and later
“Liquid acquisition” (SN: 1/15/11, p. 26) discusses two new models about how Earth got its water. But the two models are not mutually exclusive. Indeed, I wonder if perhaps two (or more) sources of water may be the only way to match all of the observed isotopic abundances. Is anybody working along these lines?
Stanley Friesen, Frederick, Md.
A combination of the two proposed scenarios—some of Earth’s water coming from the planet’s immediate surroundings at its formation, some delivered later from space—is definitely possible. Some researchers believe that this may in fact be the best solution to the puzzle. —Ron Cowen
I was glad to see the article (“Microbe swaps arsenic for key ingredient of life,” SN: