When people think of unexplored environments, they think of outer space and alien worlds. Less commonly, they think about the bottom of the ocean, or some liminal cyberspace or innerspace. But there is an even weirder environment much closer to us than any of those. Just go down.
Anyone who has been down into a cave knows things get weird quickly underground. But go down just a few miles and you’re at the mantle, superheated rock kept in solid form purely by the immense lithostatic pressure. Can you imagine what that looks like? It would take some extremely advanced technologies to make it livable in any sense. Just getting there with a drill is at the outer edge of our technological abilities.
How far does life extend down into the earth, and what percentage of the overall biome is subterranean? We know that big animals like ourselves don’t go down very far. Worms go down about a mile. Plants that rely on photosynthesis have a serious, unsurmountable problem. So the life that is deep down there is strange to us — stuff that lives for thousands of years or more, uses very little energy, and feeds on the minerals around it. Single-celled life can be very hardy, but at extreme temperatures cellular structures break down quickly. Organisms that have evolved in the deep have to rely on biological mechanisms that are alien to us surface-dwellers. However, even these extremophiles have their limits. The mantle is most of the volume and mass of the planet. While Earth is thought of as a planet abundant with life, it seems likely to me that most of this rock is as inhospitable and lifeless as Mercury.
While the depths are largely unknown and unexplored, the underground is also our refuge if the worst happens. If the bombs drop, or the big asteroid hits, or our atmosphere is lost, or the planet is thrown out of the Sun’s orbit, I am confident we can survive down there for a long while, with the help of our machines. It has all the building blocks we need, and remains remarkably stable no matter how chaotic things are on the surface. So it’s worth getting to know our underground neighborhood a little better, in case we ever feel the need to crawl into our hidey-holes.
