Could Deep Oceans Hide Life?

What could live in the world’s deepest ocean?

We aren’t talking about the Mariana Trench or Challenger Deep; recent diamond finds support a long-running theory that there is an ocean of water trapped underneath the upper mantle. As anyone in the geology know-how can tell you, plate tectonics don’t always play nice. Occasionally one plate is sucked under another (known as subduction), melted down by the lower mantle, and either left to hang around below the crust or spat back up as magma somewhere else. This process, like many others when left to Mother Nature, takes a long, long time to get going. For billions of years, this “conveyor belt” effect has repeated innumerable times all over the Earth, and- in the case of ocean subduction zones- has dragged huge amount of water along with it.

So where does all this water go? Most of the water in Earth’s mantle is squeezed into tiny spaces between the crystals of the mantle itself- hardly an ocean, no matter how much you squint your eyes. However, recent evidence suggests that an unusual formation inside the mantle led to a sort of reservoir forming far beneath our planet’s surface.

The estimated location of the underground oceans (Ricochet Creative Productions, LLC)

Which, of course, begs the question; what could live in such an environment?

Unfortunately, our horror-movie hopes of aliens or Cthulhu-like squids remain science fiction (sorry, H.P. Lovecraft). In fact, there probably isn’t much of anything living in those newly found waters. Even the most resilient of archaebacteria- a group of bacteria infamous for living in extreme conditions that have been found in Antarctic lakes, thriving in water that’s up to 9% salt (compared to the 0.9% in seawater), and floating around in boiling-hot geysers- would throw in the towel when faced with this.

Besides being chock-full of dissolved salts and minerals, the water would be just a little too hot for life. Even in the areas closest to the crust, the temperature of the mantle can reach between five hundred and nine hundred degrees Celsius– that’s more than a thousand degrees Fahrenheit. Again, even archaea can’t survive in water heated much past 100 C. In situations like these, it’s important to remember that the presence of water does not necessarily guarantee the presence of life.

So, what could live in the world’s deepest ocean? Nothing- that we know of, at least for now. However, recent discoveries of deep oceans on Enceladus and Europa suggest that that deep water, probably under high pressure and temperature, are not uncommon in the solar system. While our current definitions of life suggest that nothing should be alive at these depths, we can’t say for absolute certainty that there couldn’t be something swimming around down there, in its insanely hot salty unlivable habitat, happily defying science as we know it.

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