Fossils from the Ordovician Period

Oxygen levels link to ancient explosion of life, researchers find

Oxygen has provided a breath of fresh air to the study of the Earth’s evolution some 400-plus million years ago.


“This oxygenation is supported by two approaches that are mostly independent from each other, using different sets of geochemical records and predicting the same amount of oxygenation occurred at roughly the same time as diversification,” said Cole Edwards, the principal investigator of the study conducted when he was a postdoctoral fellow in the lab of the paper’s senior author, David Fike, associate professor in Earth and Planetary Sciences in Arts & Sciences.  The other authors are Matthew Saltzman of Ohio State University and Dana Royer of Wesleyan University in Connecticut.

“We made another link between biodiversification and oxygen levels, but this time during the Ordovician where near-modern levels of oxygen were reached about 455 million years ago,” said Edwards, assistant professor in geological and environmental sciences at Appalachian State in Boone, N.C. “It should be stressed that this was probably not the only reason why diversification occurred at that time. It is likely that other changes — such as ocean cooling, increased nutrient supply to the oceans and predation pressures — worked together to allow animal life to diversify for millions of years.”





Jerry Naunheim Jr./Washington University)

“This study suggests that atmospheric oxygen levels did not reach and maintain modern levels for millions of years after the Cambrian explosion, which is traditionally viewed as the time when the ocean-atmosphere was oxygenated,” Edwards said. “In this research, we show that the oxygenation of the atmosphere and shallow ocean took millions of years, and only when shallow seas became progressively oxygenated were the major pulses of diversification able to take place.”



“Oxygen and animal life have always been linked, but most of the focus has been on how animals came to be,” said Saltzman, professor and school director of Earth Sciences at Ohio State. “Our work suggests that oxygen may have been just as important in understanding how animals came to be so diverse and abundant.”

The photograph shows the Shingle Pass section in east central Nevada, where late Cambrian to Middle Ordovician (460 to 495 million years ago) limestone rocks are exposed. These strata were sampled for carbon and sulfur isotopic analysis in order to estimate atmospheric oxygen levels based on certain isotopic trends. At Shingle Pass, oxygen levels do not appear to increase until near the end of the evolving section (460 million years ago), and perhaps this is just about the spot where an abundance of macro fauna fossils begin to be seen, such as trilobites, corals and cephalopods. In the graph, the red line represents modeled oxygen levels using carbon and sulfur isotope trends from carbonate rocks, the blue line represents modeled oxygen levels using paired carbon isotopic data from carbonate rocks and organic matter, and the black line represents global biodiversity levels. (Graphic: Cole Edwards)

The research was funded by: Evolving Earth Foundation; Geological Society of America Graduate Student Research Grant; Paleontological Society Student Research Grant; and National Science Foundation grants EAR-0819832 and EAR-0745452.

This article originally appeared in the Source.

Leave a Comment: