It is common knowledge that life-sustaining oxygen can be produced by plants, algae, and some types of bacteria using sunlight in photosynthesis. A discovery was made by scientists regarding the possibility of having oxygen in underground ecosystems.
A World of Hidden Life
A huge biosphere teeming with billions of hidden microbes in the soil and rocks beneath our feet. Also known as "deep biosphere," this concealed world involves a patchwork of ecosystems in the Earth's deep terrestrial habitat.
For over a decade, scientists of the Deep Carbon Observatory have committed to mapping the weird wildlife of subsurface environments as part of the global research program designed to understand the quantity, movement, and forms of carbon within deep Earth. They discovered that about 70% of bacteria and archaea on Earth live in the subsurface and constitute a huge amount of carbon, about 245 - 385 times greater than the carbon mass of all humans.
Scientists initially assumed that most of these underground worlds are oxygen-deprived dead zones inhabited only by primitive microorganisms that keep their metabolisms at a crawl and scrape by on traces of nutrients. As the resources depleted, experts thought the subterranean realms became lifeless with greater depth.
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Chemical Trick for Making Oxygen
In a new research led by S. Emil Ruff, evidence was presented that challenges the previous assumptions about the deep biosphere. The research team studied the groundwater reservoirs 656 feet (200 meters) below the fossil fuel fields of Alberta, Canada. Since the huge cattle farming and agricultural industries heavily rely on groundwater, the local government actively monitors the acidity and chemical composition of the water. However, no systematic study of groundwater microbiology has been done yet.
In this study, the experts looked at deep aquifers in Alberta containing rich deposits of underground tar, oil sands, and hydrocarbon. They collected groundwater from 95 wells across Alberta and performed basic microscopy on the microbial cells from the samples.
In surveying sediments under the seafloor, the number of microbial cells usually decreases with depth since the older samples cannot sustain as much life due to the deprivation of nutrients made by photosynthetic plants and algae near the surface. However, Ruff's team discovered that the older, deeper groundwaters contain more cells than the fresher waters did. It also did not make sense that many of the microbes identified by the team were aerobic bacteria, which require oxygen to digest methane and other compounds.
Ruff and his colleagues also found that subterranean inhabitants generate and release so much "dark oxygen," like the scale of oxygen from photosynthesis in the Amazon rainforest. The underground cells diffuse enough gas to create favorable conditions for oxygen-dependent life in the surrounding groundwater and strata.
To solve these puzzles, the scientists sequenced the genomes of the community of microbes in the groundwater samples. They also tracked down the biochemical pathways and reactions that most likely produce oxygen in the light-deprived subsurface.
The answer points back to the discovery made by Marc Strous of the University of Calgary more than ten years ago. While working in a laboratory in the Netherlands, Strous noticed the strange lifestyle of methane-feeding bacteria often found in lake sediments and wastewater sludges. Instead of taking in oxygen from the surroundings like typical aerobes, these bacteria create their oxygen by breaking down nitrites using enzymes. The bacteria then use the self-generated oxygen to split methane for energy.
Breaking microbes this way is called dismutation, a process initially considered rare for generating oxygen. However, recent laboratory experiments reveal that the oxygen created from dismutation can leak out of the cells and into the surrounding medium.
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