Unlike all the planets in our solar system, Earth’s surface is about 70% liquid water, which while favorable for life, is also kind of weird, because all we know about how and when our planet was created says Earth’s surface should be dry as a bone. So, where did water come from?
The story goes like this:
Our solar system was created from the collapse of a large cloud of dust and gas. The dense ball of gas at the center ignited to create the sun, which as a young, unstable star discharged a fierce solar wind. In time this stream of charged particles pushed the leftover gas cloud farther and farther out, leaving only solid particles behind to group together into rocks, planetesimals, and finally, the rocky planets of the inner solar system that we know and love today.
And here is the problem:
Water, in the form of ice, couldn’t have been one of the solid particles that stuck around, because the beginning of the inner solar system was far too hot for frozen water to survive, and any water vapor would have been shot away by the same solar wind.
If Earth didn’t begin it’s life with H2O, how did we end up with such vast and beautiful oceans?
Where did water come from?
We know it wasn’t created here over the ages, because natural processes like combustion, breathing and photosynthesis manufacture and destroy roughly equal volumes of water – and either way, the amounts in question are so tiny that they can’t account for all the riches of the stuff on the planet today.
Since Earth’s H2O was neither part of the original package nor created here, it must have come in from far away, on meteoroids or comets or other bodies made in the outer solar system where they were far enough from that ball of fire, so frozen water can exist.
The dirty ice balls, we call comets, are a valid candidate for the source of our water, but they were ruled out when we discovered that they are far too abundant in heavy hydrogen then Earth water.
Heavy hydrogen has a neutron as well as a proton in its nucleus. ( Just to let you guys know. ) And for every million hydrogen atoms in our water, about 150 are heavy ones, while common comet water has twice that many. These different chemical signatures point that Earth’s water could not have arrived on comets.
It looks like that the most likely candidate for the water on our planet is a type of meteorite called a carbonaceous chondrite. “Chondrite” is just the label given to the class of stony meteoroids that most regularly bombard the Earth. But only carbonaceous chondrites have water – and lots of carbon, if you couldn’t figure out that from their name.
They have water in them because they formed out beyond the sun’s “frost line“, and their water has levels of heavy hydrogen identical to that of earth H2O, strongly indicating that these earth-crashers are the source or our rivers, lakes, clouds, oceans, and ice caps.
The above post was made from the following materials:
Campbell, I. H., & O’Neill, H. S. C. (2012). Evidence against a chondritic Earth.Nature, 483(7391), 553-558.
Drake, M. J. (2005). Origin of water in the terrestrial planets. Meteoritics & Planetary Science, 40(4), 519-527.
Greenwood, J. P., Itoh, S., Sakamoto, N., Warren, P., Taylor, L., & Yurimoto, H. (2011). Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon. Nature Geoscience, 4(2), 79-82.
Hauri, E. H. (2013). Planetary science: Traces of ancient lunar water. Nature Geoscience, 6(3), 159-160.
Marty, B. (2012). The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters, 313, 56-66.
Pepin, R. O. (2006). Atmospheres on the terrestrial planets: Clues to origin and evolution. Earth and Planetary Science Letters, 252(1), 1-14.
Robert, F. (2001). The origin of water on Earth. Science, 293(5532), 1056-1058.
Robert, F. (2011). Planetary science: A distinct source for lunar water?. Nature Geoscience, 4(2), 74-75.
Saal, A. E., Hauri, E. H., Van Orman, J. A., & Rutherford, M. J. (2013). Hydrogen Isotopes in Lunar Volcanic Glasses and Melt Inclusions Reveal a Carbonaceous Chondrite Heritage. Science, 340(6138), 1317-1320.