Stir a finger in a glass of water, send the water to a lab, and the sequencer will find flakes of your skin. Compare them against a library of DNA and it can tell that a person was here.
Alexander Osadchiev, an oceanologist and leading researcher at the Shirshov Institute of Oceanology, uses this picture to explain what happens when you do the same with the sea. Sequence a bottle of seawater and you read the DNA of everything that swam past lately and shed a little of itself. You never see the animals. Fungi and bacteria show up too, the creatures you only notice up close.
Then people started drilling for oil and gas, because it pays. Say three kilometres of water down to the seabed, and then another three kilometres into it. Someone sequenced the ground that came up.
Under the ocean floor there were fungi, bacteria and viruses, and plenty of them.
Osadchiev tells this as an aside, and he hedges it once. By some estimates from that drilling, the biomass of these microbes is larger than all other life on Earth put together.
By some estimates, the biomass of these viruses, fungi and bacteria in the seabed exceeds the biomass of all other living things on Earth.
По некоторым оценкам, по этому бурению, биомасса этих вирусов, грибов и бактерий в морском дне превышает всю биомассу всего остального живого на Земле.
— Alexander Osadchiev, Gleb Solomin Podcast, 08:57
For us, he says, the conditions down there are unnatural. For them they are normal. That is where the stakes for an ordinary reader sit: if people learn to use these organisms, he thinks they are a key to ageing and to new medicines, antibiotics among them. He is careful to add that humans are only taking the first steps.
Other measurements give smaller shares, and it is fair to set them next to his. A 2012 paper in the Proceedings of the National Academy of Sciences, by Jens Kallmeyer and colleagues, counted the microbes in sediment beneath the seafloor: about 2.9·10^29 cells, holding 4.1 petagrams of carbon. That is roughly 0.6% of all living biomass on Earth. A 2018 PNAS estimate by Yinon Bar-On and colleagues puts all life at about 550 gigatons of carbon, around 80% of it plants. The deep subsurface holds about 15% of the total.
So the published figures put the underground biosphere in the hundreds of millions of times... no. They put it well below the whole of everything else. Still, 15% sits beneath our feet, out of sight, and the seabed alone carries trillions upon trillions of cells.
Nobody went down there looking for them. The drillers wanted oil and gas, and the mud turned out to be full of life.
