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Imagine taking all of the trees, grass, animals, insects, fish, coral, and bacteria on the surface of the Earth and in the sea. Basically, every living thing on the planet.
If you were to add it all up, all of the biomass, it would be quite a bit.
Yet according to some scientists, that might not even account for most of the life on Earth.
Learn more about the Deep Biosphere on this episode of Everything Everywhere Daily.
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To start, when I’m talking about the deep biosphere, I’m not talking about soil, the layer where all the worms and roots are. For all practical purposes, I’m calling that the surface.
What I’m talking about, is everything below that. Starting at about 2 meters down all the way to 5 kilometers down on land, and everything below the bottom of the seafloor, down to about 10 kilometers in the ocean.
You might be thinking, how is this possible? If you go down that far, you encounter solid rock. There is no light. There is no oxygen. There is too much heat and pressure. How is it possible that anything could live, yet alone to have so much life that might rival everything on the surface?
Well, to explain that we have to back up a bit.
If you think that life can’t possibly exist that far down, you aren’t alone. No one ever really considered it. The idea defies everything we know about what makes life possible.
Moreover, it is extremely difficult to explore deep beneath the earth. The only way to do it is via drilling or very deep mining, and our ability to go really deep is a rather recent development.
In the 1920, researchers noted that some oil wells were bringing up hydrogen sulfide and bicarbonates. These things are normally the product of bacteria, but the wells were deep enough that there shouldn’t be any life.
Nonetheless, when they took samples of the water from the well, they were able to grow bacteria.
In the 1930s, scientists were able to grow bacteria that came from coal. Not only did they find bacteria, but when they heated the coal to 160 Celcius, well above the boiling point of water, the bacteria started to rapidly grow!
As ocean drilling became a thing, whenever samples were taken from ocean sediment or below, they always found bacteria.
However, most of this evidence was dismissed. The consensus view was that life was impossible for all the reasons I gave before. They assumed that any bacteria found from such depths or under such conditions must have been contaminated from the surface.
Nonetheless, the same results kept coming in.
In the 1980s, the United State’s Deep Sea Drilling Project began taking core samples from below the surface of the ocean, and they found more microbes. Lots of microbial life in fact.
The thing which began to change everyone’s perception was a paper written in 1992 by Thomas Gold from Cornell University. Gold wasn’t a biologist or even a geologist. He was an astronomer.
His paper titled “The Deep, Hot Biosphere” resulted in a fundamental shift in how we viewed microbial life below the surface of the Earth.
His article began as follows:
“New forms of microbial life are being discovered in such abundance deep inside the Earth that some scientists are beginning to suspect that the planet has a hidden biosphere extending miles down whose total mass may rival or exceed that of all surface life. If a deep biosphere does exist, scientists say, its discovery will rewrite textbooks while shedding new light on the mystery of life’s origins. Even skeptics say the thesis is intriguing enough to warrant new studies of the subterranean realm.”
In the 30 years since the paper was written, the evidence has only gotten stronger to support Gold’s hypothesis.
They have found all three domains of life deep in the Earth. These aren’t plants, animals, and fungi, which are kingdoms, but one step up, the various single cell life. Archaea, Bacteria, and Eukarya.
They have found nematodes, which are tiny animals, living at the bottom of the deepest mine in the world in South Africa.
They have found evidence of life in the mud volcanoes at the bottom of the Mariana Trench, the deepest place in the ocean. This mud is being brought up from hundreds or thousands of meters below that.
The reason why there might be more microbial life below the surface of the Earth is just that there is so much of it and it goes down so far. If you think about it, most life on the surface of the Earth is only about 1 or 2 meters up or down from the surface. Microbes, however, keep going for miles and miles.
So how do they do it? How can life live down there when it’s mostly rock?
For starters, solid rock really isn’t solid. There are very small pores in the rock about the size of a micron. Just big enough for microbes to fit. Some rocks which are sedimentary might be much more porous, enough for water to flow through them.
What do they live on? The microbes that far down have found novel ways to get energy, including using things like hydrogen, sulfur, and iron, and food. Almost all of them are anaerobic, which means they do not use oxygen.
Moreover, they have extremely slow metabolisms. They can lie dormant for an extremely long time.
By extremely long, I do mean extremely long. In 2020, Japanese researchers found bacteria taken from coring samples under the seafloor which they believe have been dormant for 100 million years!
Moreover, they were able to get them to reproduce once they were taken into the lab.
There is an incredible diversity of life that far down. There are estimates that there might be more than 1 trillion species of microbes on and in the Earth
So what are the implications of this? If there are all these microbes below us, why does that matter?
The biggest implication is that if life can exist so far below the surface, even in a dormant state, then it might be possible elsewhere. Perhaps somewhere like Mars. Just looking on the surface might not be sufficient if we are looking for signs of life. Even if life is no longer on the surface of Mars, it might still be somewhere below the surface.
Another implication is that the microbes in the Earth may have had a role in the evolution of life on the planet. It might not be that left started on the surface and went down, it might be that it started below and came up.
So, the next time you are walking around with grass below your feet, realize that most of the life below you isn’t the grass, it is the tons and tons of microbes and bacteria which are filling up the pores in the rocks.