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The mysterious microbes living deep inside the earth — and how they could help humanity
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The mysterious microbes living deep inside the earth — and how they could help humanity It may seem like we're all standing on solid earth right now, but we're not. The rocks and the dirt underneath us are crisscrossed by tiny little fractures and empty spaces. And these empty spaces are filled with astronomical quantities of microbes, such as these ones. The deepest that we found microbes so far into the earth is five kilometers down. So like, if you pointed yourself at the ground and took off running into the ground, you could run an entire 5K race and microbes would line your whole path. So you may not have ever thought about these microbes that are deep inside earth's crust, but you probably thought about the microbes living in our guts. If you add up the gut microbiomes of all the people and all the<b> animals </font></b>on the planet, collectively, this weighs about 100,000 tons. This is a huge biome that we carry in our bellies every single day. We should all be proud. But it pales in comparison to the number of microbes that are covering the entire surface of the earth, like in our soils, our rivers and our oceans. Collectively, these weigh about two billion tons. But it turns out that the majority of microbes on earth aren't even in oceans or our guts or sewage treatment plants. Most of them are actually inside the earth's crust. So collectively, these weigh 40 billion tons. This is one of the biggest biomes on the planet, and we didn't even know it existed until a few decades ago. So the possibilities for what life is like down there, or what it might do for humans, are limitless. This is a map showing a red dot for every place where we've gotten pretty good deep subsurface samples with modern microbiological methods, and you may be impressed that we're getting a pretty good global coverage, but actually, if you remember that these are the only places that we have samples from, it looks a little worse. If we were all in an alien spaceship, trying to reconstruct a map of the globe from only these samples, we'd never be able to do it. So people sometimes say to me, "Yeah, there's a lot of microbes in the subsurface, but ... aren't they just kind of dormant?" This is a good point. Relative to a ficus plant or the measles or my 's guinea pigs, these microbes probably aren't doing much of anything at all. We know that they have to be slow, because there's so many of them. If they all started dividing at the rate of E. coli, then they would double the entire weight of the earth, rocks included, over a single night. In fact, many of them probably haven't even undergone a single cell division since the time of ancient Egypt. Which is just crazy. Like, how do you wrap your head around things that are so long-lived? But I thought of an analogy that I really love, but it's weird and it's complicated. So I hope that you can all go there with me. Alright, let's try it. It's like trying to figure out the life cycle of a tree ... if you only lived for a day. So like if human life span was only a day, and we lived in winter, then you would go your entire life without ever seeing a tree with a leaf on it. And there would be so many human generations that would pass by within a single winter that you may not even have access to a history book that says anything other than the fact that trees are always lifeless sticks that don't do anything. Of course, this is ridiculous. We know that trees are just waiting for summer so they can reactivate. But if the human life span were significantly shorter than that of trees, we might be completely oblivious to this totally mundane fact. So when we say that these deep subsurface microbes are just dormant, are we like people who die after a day, trying to figure out how trees work? What if these deep subsurface organisms are just waiting for their version of summer, but our lives are too short for us to see it? If you take E. coli and seal it up in a test tube, with no food or nutrients, and leave it there for months to years, most of the cells die off, of course, because they're starving. But a few of the cells survive. If you take these old surviving cells and compete them, also under starvation conditions, against a new, fast-growing culture of E. coli, the grizzled old tough guys beat out the squeaky clean upstarts every single time. So this is evidence there's actually an evolutionary payoff to being extraordinarily slow. So it's possible that maybe we should not equate being slow with being unimportant. Maybe these out-of-sight, out-of-mind microbes could actually be helpful to humanity. OK, so as far as we know, there are two ways to do subsurface living. The first is to wait for food to trickle down from the surface world, like trying to eat the leftovers of a picnic that happened 1,000 years ago. Which is a crazy way to live, but shockingly seems to work out for a lot of microbes in earth. The other possibility is for a microbe to just say, "Nah, I don't need the surface world. I'm good down here." For microbes that go this route, they have to get everything that they need in order to survive from inside the earth. Some things are actually easier for them to get. They're more abundant inside the earth, like water or nutrients, like nitrogen and iron and phosphorus, or places to live. These are things that we literally kill each other to get ahold of up at the surface world.  |
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