Hunting for life deep within the earth
Along with the life found at the ocean floor in the deepest place on the planet, the Challenger Deep in the Mariana Trench, there are now indications that life may exist 10 km further down within the crust itself. Earth scientists from Utrecht University and elsewhere have found complex organic molecules trapped in rock fragments from the earth’s crust that have been spewed out by enormous mud volcanoes on the ocean floor. They published their results in Proceedings of the National Academy of Sciences (PNAS).
We can see with our own eyes that life is present on the earth’s surface. We also know that there are living organisms smaller than can be seen with the naked eye. But we rarely consider the life deep beneath our feet, buried far below in the earth's crust. Just how deep life could exist and how it obtains its energy remain unanswered questions.
Mud volcanoes and organic materials
Enormous mud volcanoes above the spot where the Pacific Plate disappears under the Philippine Plate spew out rock fragments originating around 20 km below the ocean floor. The fluids released from the lower plate produce chemical reactions in the rock formations deep within the lithosphere. This process is called serpentinisation, and it may provide the energy for lifeforms deep in the earth.
Message in a bottle
Encased in chunks of these serpentinised rocks is organic material. “It is a kind of message in a bottle,” explains Oliver Plümper, earth scientist at Utrecht University and primary author of the article. “Although we cannot specify the exact origin of the organic material, our chemical analysis suggests that there is life deep within or even underneath the mud volcano.”
These findings agree with the researchers’ calculations based on the heat limit for life, namely 122 degrees Celsius, and the temperatures that the researchers expect to find under the mud volcano. This suggests that life can exist even 10 km below the Mariana mud volcanoes.
“The mud volcanoes offer a unique window into the deep underground, and allow us to trace back processes that would otherwise remain concealed,” says Helen King, earth scientist at Utrecht University and co-author of the publication. “Finding organic material in the ejected rock fragments was amazing given that they indicate the possibility of a deep biosphere under the mud volcanoes.”
This research contributes to the Origins Centre, the new national research initiative derived from the National Science Agenda looking into the origin of life. Inge Loes ten Kate, astrobiologist at Utrecht University and member of the core group of the Origins Centre explains: “These results produce entirely new insights into the habitability of our planet and what makes the earth unique in comparison with the rest of our solar system. This is one of the main themes of the new Origins Centre.”
Plümper O., King H.E., Geisler T., Liu Y., Pabst S., Savov, I.P., Rost D., Zack T. (2017) Subduction zone forearc serpentinites as incubators for deep microbial life. Proceedings of the National Academy of Sciences of the United States of America (PNAS)