How much life is on Earth?

Posted by Kate Taylor

The total mass of all life on Earth is about one third less than thought, a new analysis has indicated.

According to previous estimates about one thousand billion tons of carbon are stored in living organisms, of which 30 percent are single-cell microbes in the ocean floor and 55 percent land plants.

But a team from the GFZ German Research Centre for Geosciences and University of Potsdam now says there's a lot less carbon than thought stored in subseafloor microbes - about four billion tons in all.

Previous estimates were based on drill cores that were taken close to shore or in very nutrient-rich areas.

"About half of the world's ocean is extremely nutrient-poor. For the last 10 years it was already suspected that subseafloor biomass was overestimated," says Dr Jens Kallmeyer. "Unfortunately there were no data to prove it."

He and his team collected sediment cores from areas that were far away from any coasts and islands. The six-year work showed that there were up to one hundred thousand times less cells in sediments from open-ocean areas - often dubbed 'deserts of the sea' due to their extreme nutrient depletion - than were found in coastal sediments.

With these new data the scientists recalculated the total biomass in marine sediments and found these new, drastically lower values.

"Our new results show the need to re-examine the other numbers as, for example, the amount of carbon in deep sediments on land," says Kallmeyer.

In particular, he says, there's still little research into the deep biosphere - life found a kilometer or so down inside Earth's crust.