The trapping of carbon in buried sediment allowed oxygen to accumulate in the atmosphere 500 million years ago. That buried carbon came to form fossil fuel deposits and carbon-rich rocks like the black shale pictured above. Photo by University of Wisconsin
MADISON, Wis., Jan. 3 (UPI) -- Why did atmospheric oxygen spike 500 million years ago? Research has shown photosynthesis had been around for at least 2.5 billion years prior to the oxygen uptick and subsequent Cambrian explosion -- the dramatic diversification of animal life.
Researchers at the University of Wisconsin-Madison believe the raw materials of fossil fuels may explain the phenomenon.
In a new paper published in the journal Earth and Planetary Science Letters, scientists argue the burial of plant matter -- and the denial of the oxidation process -- allowed for the accumulation of oxygen in the atmosphere.
Coal, oil and natural gas form through the slow breakdown of buried organic matter. Instead of becoming oxidized at the surface, the raw carbon becomes pressure-cooked between layers of earth.
If there is less oxidation happening, less oxygen is being converted into carbon dioxide, and thus oxygen builds up in the atmosphere. Researchers surmised historic records would reveal a link between oxygen levels and sedimentary rock deposition -- the more organic matter becomes subsumed by sediment, the more oxygen accumulated in the atmosphere.
Researchers compared prehistoric oxygen levels with corresponding rock data provided by Macrostrat, an amalgamation of North American geologic information. Their analysis revealed a link between oxygen and sediment.
"It's a correlation, but our argument is that there are mechanistic connections between geology and the history of atmospheric oxygen," postdoctoral fellow Jon Husson said in a news release.
Husson and his advisor Shanan Peters, a professor of geoscience, found a link between sediment deposition and fossil fuel fields, like those found in the Permian Basin in Texas and the Pennsylvania coal fields of Appalachia.
"Burying the sediments that became fossil fuels was the key to advanced animal life on Earth," Peters added.
Researchers aren't exactly sure what geologic processes triggered spurts of increased sediment storage, but suspect altered tectonic plate movements and shifts in magmatic conduction in the mantle both played a role.