The boundaries of life: how deeply has the biosphere “bitten” into the earth’s crust? (6 photos)

Where are the boundaries of the biosphere? It’s a good question, especially since there hasn’t been a clear answer to it yet. With the upper limit, everything is clear: when leaving the planet, all living things are quickly sterilized by solar radiation and vacuum. But with the lower boundary of the biosphere, everything is not so clear.





Already a hundred meters underground, such terrible creatures can be found. The photo shows a cave salamander.

The deepest point where people have discovered life is the Challenger Deep, the bottom of the Mariana Trench. There are no more fish there; they seem to be unable to withstand such water pressure. But at depths of 10-11 kilometers, numerous invertebrates live, such as sea cucumbers. They are accompanied by incredibly large single-celled organisms, the length of which can reach 20 centimeters!



No, this is not a brain thrown to the mercy of fate, but an amoeba-like single-celled, xenophyophore.

And yet, by the standards of other deep ecosystems, life here is quite comfortable. Benthic ecosystems receive enormous amounts of resources in the form of deep-sea snow - the remains of organisms that died at higher ocean levels.





Organic particles continuously and very slowly fall lower and lower into the ocean. At great depths it resembles real snowfall. Snowfall of food!

Cave dwellers, for example, have it much worse. If the first tens and hundreds of meters are actively supplied with organic matter from the surface, then at the bottom of deep caves, 1-2 kilometers underground, there are extremely few resources. The main source of energy at this depth is bacteria that destroy rocks.



Some large caves form separate ecosystems that can only be found in enclosed spaces.

They are devoured by white eyeless snails and woodlice, which, in turn, are hunted by equally blind arachnids. Fungi grow on the remains of their feasts, and their numbers are kept in check by small arthropods. This is a blind world, each inhabitant of which has an almost extrasensory sensitivity to smells and vibrations.



All living creatures living in caves are almost always colorless and have no eyes.

But life exists not only in caves, but also right in the rock mass! Moreover, there is so much of it that biologists had to invent a new term - the deep biosphere. It includes all organisms living at depths below 1 meter from the soil level. And there are a lot of them there. Research shows that at depths of up to 500 meters, the density of organisms ranges from 10^4 to 10^8 single-celled organisms per gram. For reference, in fertile soil there are on average 10^9 single-celled organisms per gram. At the moment, researchers have been able to detect bacteria at a depth of 2200 meters, and according to theoretical calculations, they can live even deeper, up to 5 kilometers.



The unique conditions of life underground lead to unique evolutionary solutions. Here is a colony of underground bacteria Jeongeupia sacculi. Despite the fact that they are primitive non-nuclear organisms, bacteria within the colony are divided into specializations. They behave like a real multicellular organism!

According to recent estimates, up to 90% of prokaryotic species live in the deep biosphere, and their mass can reach up to 15% of the mass of all living things on the planet. Yes, there are very few resources in the rocks, but the conditions are very constant; they may not change for millennia. And primitive single-celled organisms needed very little to maintain life, so they organized millions of microscopic closed ecosystems.