The "cellar" of the earth is teeming

Quadrillions of microbes live in the continental underground

Microbes from a depth of around 2, 000 meters under the electron microscope © Hiroyuki Imachi / JAMSTEC
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Hidden lifeworld: Kilometers deep in the earth's crust exists surprisingly much life. Despite permanent dark, enormous pressure and barren nutrients, the "cellar" of our continents harbors several hundred quadrillion cells, new estimates suggest. Bacteria appear to be much more abundant than archaea, the researchers report in the journal Nature Geoscience.

Even miles below our feet teeming with life: Whether below the oceans or on the continents - inside the earth's crust, there are unique ecosystems to marvel at. Scientists have repeatedly come across the microbial inhabitants of this underworld in recent years. They even found bacteria living under 2, 500 meters below the ocean floor.

Life in the "basement" of the Earth defies darkness, scorching heat and high pressure and is likely to account for a significant portion of our planet's prokaryotic biomass. Nevertheless, this so-called deep biosphere is still a big unknown to scientists: how many organisms live there exactly and which factors influence their occurrence?

Even inside the earth, there is life. © Adventtr / istock

How many cells?

"While significant progress has been made in exploring the subsurface marine biosphere in the past, estimates of continental biomass are currently subject to great uncertainties, " write Cara Magnabosco of the Simons Foundation in New York and her colleagues. Therefore, they have now devoted themselves to this knowledge gap.

For their study, the researchers evaluated data from more than 200 publications with approximately 3, 800 measurements of cell concentration and biodiversity in the continental subsoil. The data came mainly from samples from North America, Europe and Japan. Taking into account influencing factors such as temperature, depth and rock type, the team calculated on this basis how many cells live in total in this underworld. display

Supervised by an order of magnitude

The result: "We estimate that the continental subsoil harbors two to six times 10 29 cells, " write the scientists. Although this number is not set in stone, it is particularly uncertain because there were hardly any samples from South America, Africa and Australia available for the analyzes.

"As long as these regions do not show dramatically different biomass trends, however, our new estimate means that previous calculations will sometimes outnumber biomass in the deep biosphere by one order of magnitude have, "said Magnabosco and her colleagues.

More bacteria than archaea

But what about biodiversity? What determines where the biotic community of the underworld is particularly diverse? The researchers could only answer this question in part. Thus, they failed to identify certain factors that can reliably predict the diversity of the deep biosphere.

However, it emerged that bacteria on the continental surface appear to be much more abundant than archaea. These bacteria-like organisms belong to the oldest forms of life in the world and are especially often found in the extreme environments.

The evaluations also showed that the composition of the bacterial community seems to be mainly dependent on the rock.

Many questions

As the scientists emphasize, despite their new findings, many questions remain unanswered. The nature of life in the cellar of the earth remains a mystery for the time being. "Understanding this life can in the future lead to a better understanding of the carbon cycle in the deep biosphere and also help in the search for life forms on other planets, " they conclude. (Nature Geoscience, 2018; doi: 10.1038 / s41561-018-0221-6)

(Nature, 26.09.2018 - DAL)