On Earth circa four billion years ago, life was hard. Frequent asteroid strikes turned parts of the planet into molten rock. Food and livable spaces were few and far between. What was a microbe to do to survive? Some very early life could have made it by staying deep—living as far as six miles below the seafloor.
(From National Geographic / by Claudia Geib) — That’s the implication from a new study that found signs of microbes alive today below the deepest place on Earth, the vast underwater canyon called the Mariana Trench. (Also see pictures that reveal one of the last unexplored places on Earth near the Mariana Trench.)
The trench is part of a subduction zone, where the Pacific tectonic plate slips beneath the Philippine Sea plate. The surrounding seafloor is littered with hydrothermal vents and mud volcanoes, churning out ingredients from the deep Earth.
In the new study, published today in the Proceedings of the National Academy of Sciences, researchers sampled mineral-rich mud from the South Chamorro seamount, a mud volcano near the Mariana Trench fueled by the subduction zone below it. Though the team did not find intact microbes, they did discover tantalizing traces of organic material, which may add to evidence that life can survive in the most extreme of environments.
“This is another hint at a great, deep biosphere on our planet,” says study leader Oliver Plümper, a researcher at the Netherlands’ Utrecht University. “It could be huge or very small, but there is definitely something going on that we don’t understand yet.”
Life may be able to survive so deep because subduction zones are relatively cool; magma doesn’t hit the sinking crust until it reaches a lower point in the mantle. As such, Plümper extrapolated that the known temperature limit of life—around 250 degrees Fahrenheit—wouldn’t come until a depth of at least six miles below the ocean floor.
That could make these microbes the deepest life known on our planet, trumping microbes found in seafloor sediment as much as three miles down.
“I think the main take-home of this paper is how this has the potential to place life at some of the deepest environments on the planet,” says Matthew Schrenk, a geomicrobiologist at Michigan State University who studies the microbial ecosystems that live off serpentinization.
“If we’re looking for the depth limits of the biosphere, this could extend it by a lot.”
Read the full article here: http://news.nationalgeographic.com/2017/04/deepest-life-earth-mariana-trench-astrobiology-science/