Ocean Crust Teems with Life
The research, just published in the journal PLoS One, showed that a significant number and amount of bacterial forms were present, even in temperatures near the boiling point of water. The study provides new information about evolutionary mechanisms and the limits of life on Earth. This can help astrobiologists identify environments on other worlds that might be habitable for life as we know it.
“This is a new ecosystem that almost no one has ever explored,” said Martin Fisk, a professor in the College of Oceanic and Atmospheric Sciences at Oregon State University. “We expected some bacterial forms, but the long list of biological functions that are taking place so deep beneath the Earth is surprising.”
Oceanic crust covers about 70 percent of the surface of the Earth and its geology has been explored to some extent, but practically nothing is known about its biology – partly because it’s difficult and expensive, and partly because most researchers had assumed not all that much was going on.
The temperature of the sediments and rock increases with depth, and scientists now believe that the upper temperature at which life can exist is around 250 degrees. The ocean floor is generally composed of three levels, including a shallow layer of sediment; basalt formed from solidified magma; and an even deeper level of basalt that cooled more slowly and is called the “gabbro” layer, which forms the majority of ocean crust.
A research expedition drilled more than 4,600 feet into this formation, into rock that was very deep and very old, and found a wide range of biological activity. Microbes were degrading hydrocarbons, some appeared to be capable of oxidizing methane, and there were genes active in the process of fixing, or converting from a gas, both nitrogen and carbon.
The findings are of interest, in part, because little is known about the role the deep ocean crust may play in carbon storage and fixation. Increasing levels of carbon dioxide, a greenhouse gas when in the atmosphere, in turn raise the levels of carbon dioxide in the oceans.
The researchers also noted that methane found on Mars could be derived from geological sources, and concluded that subsurface environments on Mars where methane is produced could support bacteria like those found in this study.
“These findings don’t offer any easy or simple solutions to some of the environmental issues that are of interest to us on Earth, such as greenhouse warming or oil spill pollution,” Fisk said. “However, they do indicate there’s a whole world of biological activity deep beneath the ocean that we don’t know much about, and we need to study.”
Microbial processes in this expansive subseafloor environment “have the potential to significantly influence the biogeochemistry of the ocean and the atmosphere,” the researchers wrote in their report.