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One third of Earth’s biomass may still lie undiscovered in the most unexpected places, deep ocean subsea floors.
Texas A&M oceanographer Heath Mills’ research is at the forefront of this watery new frontier.
In the past decade, the discovery of deep-sea microbes has challenged what scientists consider the basis of life.
“What we knew of as biology and the requirements for life seven to ten years ago suggested nothing could live that deep down; and yet, everywhere we have drilled looking for life we have found it,” Mills said.
The biodiversity is astounding. From the compounds these deep-sea creatures breathe; nitrate, iron, manganese, and sulfate; to the places they thrive; hydrothermal vents and the dark cold miles beneath the ocean surface; these microbes are far from conventional.
 Microbial community collected from a shallow subsurface sediment sample taken from the Gulf of Mexico
“You may think life on Earth means bright sunshine, an abundance of oxygen, and warm temperatures. Now we see that even more so life on earth is cold, dark, and doesn’t involve oxygen,” Mills said. “Our planet holds more life under the conditions we see as extreme than what we see here.”
The implications of biology in deep-sea exploration go further than just finding new microbes.
Subsurface environments look similar to what scientists predict of early Earth. Understanding the processes and metabolic activities of deep-sea microbes could provide insight into the origins and evolution of life itself.
This research also expands what is known to be the true habitable zone on this planet. Some scientists are extrapolating that if life can exist at these extreme conditions; life could possibly be on other planets.
Mills’ molecular biology research has taken him around the world, from the coast of Japan to the Great Barrier Reef to the middle of the Atlantic Ocean, with the Integrated Ocean Drilling Program (IODP), an international research program that retrieves sub-seafloor sediments and rocks.
 Mills on board Expedition 336, sampling sediment from the Mid-Atlantic Ridge
Mills’ research is a breakthrough for the IODP, which has historically concentrated on the physical formations and behavior of Earth’s processes.
“What we are seeing now is that a lot of these processes are active and there is more biomass, activity, and biological alteration of the subsurface than what was previously considered,” Mills said. “Just as chemistry, hydrology, and geology changes the subsurface, so does biology. And microbes may be altering it at faster rates and on a broader scale than what we assumed.”
The future of deep-sea microbial research lies in exploring deeper and more diverse locations.
Mills participated on the IODP’s latest expedition, which explored beyond the sediment and into the basalt-the hard basement material beneath the sediment, or soil.
“This transition into examining basement communities is a needed step,” Mills said.
“To understand the life on this planet you must understand the subseafloor biosphere,” Mills said.
Texas A&M is the IODP’s United States Implementing Organization responsible for vessel and drilling operations, ship- and shore-based science laboratories, and housing the samples in core repositories.
Learn about Mills’ past expeditions with the IODP and follow his future work on his blog.
Katy Ralston, '12
March 29, 2012
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