A team of researchers from the Graduate School of Oceanography at the University of Rhode Island and their collaborators have found that numerous microbes living in ancient sediments under the seabed are supported mainly by chemicals created by the natural radiation of water molecules.
The team found that the formation of these chemicals was greatly enhanced by minerals in marine sediments. Contrary to the conventional wisdom that life in sediment feeds on photosynthetic products, an ecosystem fueled by irradiated water begins just meters from the seabed in much of the open ocean. This radiation-flooded world is one of the largest ecosystems on Earth by volume.
“This work provides an important new perspective on the availability of resources that subsurface microbial communities can use to sustain themselves. This is fundamental to understanding life on Earth and limiting the habitability of other planets such as Mars.”Justine Sauvage, Research Fellow, University of Gothenburg
The process behind the research team’s findings is called water radiolysis, which is the splitting of water molecules into hydrogen and oxidants as a result of exposure to natural radiation. The resulting molecules become the main source of food and energy for microbes living in sediments.
Marine sediments actually enhance the production of these beneficial chemicals. If there is the same amount of radiation in clean water and in wet sediments, there will be much more hydrogen in wet sediments. Precipitation makes hydrogen production much more efficient.
Why this process is enhanced in wet sediments is unclear, but scientists speculate that the minerals in the sediments may behave like semiconductors, making the process more efficient.
These discoveries were the result of a series of laboratory experiments conducted at the Rhode Island Nuclear Research Center. Scientists irradiated vials of wet sediment from various locations in the Pacific and Atlantic oceans collected by the Integrated Ocean Drilling Program and US research vessels. They then compared hydrogen production with similarly irradiated seawater and distilled water tubes. The sediment increased the results 30 times.
“This research is a unique combination of sophisticated laboratory experiments integrated into a global biological context.”Arthur Spivak, URI professor of oceanography
If life in subterranean marine sediments and other subterranean environments can be sustained through the natural radioactive splitting of water, then perhaps life can be sustained in the same way in other worlds. Some of the same minerals are present on Mars, and as long as these wet catalytic minerals are present, this process will continue. If the production of radiolytic chemicals at high rates can be catalyzed in the humid interior of Mars, then life can potentially be kept at the same level as in marine sediments.
The research team’s findings also have implications for the nuclear industry, including how to store nuclear waste and how to manage nuclear accidents. If nuclear waste is stored in sediment or rocks, it can generate hydrogen and oxidants faster than pure water. This natural catalysis can make these storage systems more aggressive than is commonly believed.
The next steps of the research group will be to study the effect of hydrogen production through radiolysis in other environments on Earth and beyond, including the oceanic crust, continental crust and the interior of Mars. They will also seek to deepen understanding of how underground microbial communities live, interact and develop when their primary energy source comes from the natural radiolytic breakdown of water.