Buried inside 86 million-year-old red clay, they are surviving on tiny amounts of oxygen - so little that they barely qualify as life. Indeed, the discovery could have implications for the search for life on alien planets, as it implies life may need much fewer resources than thought.
A team from Aarhus University in Denmark, Germany's Potsdam University and the University of Rhode Island collected mud samples from sediment columns deep below the ocean floor, on a cruise along the equator and into the North Pacific Gyre.
Sediment columns build up layer by layer on the seafloor and can be kilometers thick, with the youngest material on top and the oldest on the bottom. Using needle-shaped oxygen-sensors, the team discovered that the bacteria living in these sediments are alive and actively using up oxygen - albeit very, very slowly.
The microbes turn over their sediment biomass at a rate of once every few hundred years to once every few thousand years.
This may reflect cell division, but could also simply indicate a one thousand year cell repair cycle, says the team.
At the bare minimum, microbes need energy to maintain an electric potential across their membrane and to keep their enzymes and DNA working. The scientists suspect these microbial communities may be living at the minimum energy requirement needed to subsist.
"But, it’s clear that this microbial community - which has not received food from the outside world since the dinosaurs walked the earth - is still alive and active," says the team.
"The study suggests that all the knowledge scientists have accumulated about fast-growing laboratory microorganisms probably doesn’t apply to slow life beneath the ocean." Via TG Daily