It may seem like scientists spend an inordinate time studying water but there’s a pretty good reason for that. Water is fundamental to all forms of life on Earth so understanding its origins and what roles it plays is crucial to understanding how life came to be and where we might find it. The vast majority of Earth’s water is contained in its oceans which were thought to have formed when comets bombarded its surface, seeding them across the world. However recent research has shown that the oceans may have formed in a different way and that Earth may have much more water contained in it than previously thought.
A recent study done by Steven Jacobsen and his team at Northwestern University has revealed that Earth has a subsurface reservoir that may contain 3 times the volume of the Earth’s surface oceans. They discovered this information by using data from a wide variety of seismometers, those instruments that measure the intensity of the pressure waves of earthquakes, and figuring out how the waves travelled through the Earth’s interior. This is nothing new, it’s how we’ve figured out the rough compositions of the different layers of the Earth’s inner layers previously, however Jacobsen postulated that water in ringwoodite would slow the waves. After testing a sample of ringwoodite to confirm this theory (shown above) his team found data to support the existence of a large layer of ringwoodite in the Earth’s mantle. Whilst this isn’t a subsurface ocean like some heavenly bodies in our solar system have it is a rather interesting discovery, one that supports an entirely different theory of how our surface oceans formed.
The initial hypothesis (at least the one I’m familiar with) is that the Earth bound itself together out of all the varying bits of debris that existed after the sun had formed itself. At this point Earth was a ball of lava, a fiendishly unfriendly environment devoid of any kind of life. Then, as the planet cooled, comets rained down on its surface, supplying the vast amounts of water we now see today. The discovery of this layer of ringwoodite on the other hand suggests that the water may have been present during the initial formation and that instead of other comets providing all the water it instead seeped up, filling all the crevices and crags of the Earth’s surface. It’s interesting because it now links Earth more directly to our other celestial neighbours, those which you’d never consider Earth-like at all.
Saturn’s Europa and Jupiter’s Ganymede for instance are both hypothesized to have vast bodies of water under their surfaces. Up until this discovery you would be forgiven for thinking that their initial formation was likely due to their immediate environment (I.E. those massive gas giants right next to them) however it’s more likely that all heavenly bodies form along a similar path. Thus oceans like ours are probably more likely than not for planets of similar size to ours. Of course there are also numerous other factors that can push things in one way or another (see Mars and Venus for examples of Earth like planets are nothing like Earth) but such similarities really can’t be ignored.
In all honesty this discovery surprised me as I had always been a subscriber to the “comet bombardment” theory of Earth’s oceans. This evidence however points towards an origin story where water formed a core part of Earth’s structure, only to worm its way to the surface long after it cooled. Come to think of it this probably also explains (at least partially) how Earth’s atmosphere likely came to existence, the gases slowly seeping out until it was blanketed in carbon dioxide, only to be turned into the atmosphere we know today by plants. I’m keen to see what other insights can be gleaned for this data as I’m sure this isn’t the only thing Jacobsen’s team discovered.
Correction: My good friend Louise correctly pointed out that our atmosphere started off being almost completely carbon dioxide and only had the composition we know today thanks to plans. She also pointed out I used the wrong “it’s” in the title which, if I didn’t know any better, would say to me that she wants to be my copy editor 😉