About 71 percent of the Earth’s surface is covered by water, and vast quantities of water are also locked up in minerals on and beneath the surface. This image of Earth comes from NASA’s Earth Polychromatic Imaging Camera (EPIC) on NOAA’s Deep Space Climate Observatory (DSCOVR), orbits Earth from a distance of about 1 million miles away. (NASA)
One of the enduring puzzles of our planet is why it is so wet.
Since Earth formed relatively close to the sun, planetary scientists have generally held that any of the water in the building blocks of early-forming Earth was baked out and so was unavailable to make oceans or our atmosphere.
That led to theories explaining the oceans and wet atmosphere of Earth as a later addition, brought to us by meteorites and comets formed beyond the solar system’s so-called “snow line,” where volatile compounds such as water can begin to condense into ice.
This snow line is a general area between Mars and Jupiter, and that means under this theory that our water would have had to come from awfully far away. Further complicating this view is that the isotopic makeup of that distant water ice is somewhat different from ...