Mass Extinctions on Earth Coincided With Out-of-Whack Carbon Cycles

Fossil skeleton of a Pteradactyl, from the British Museum's collection

Previous mass extinctions in Earth’s history can illuminate how much carbon human civilization can pump into the environment before risking a catastrophic climate change — and that point may be coming up within a century.

That’s the conclusion of Daniel Rothman, a geophysicist at the Massachusetts Institute of Technology, who built a database of fossil records going back half a billion years. Rothman found the periods in which large percentages of existing species died off coincided with big swings in the carbon isotopes found in those records, suggesting the planet’s carbon cycle was out of whack.

“It implies changes in the carbon cycle are likely both an indication of some kind of serious change and possibly a player in amplifying those changes,” Rothman told Seeker.

In a stable environment, carbon ebbs and flows from organic materials. Carbon dioxide fuels photosynthesis in plants, which store it as they grow; when they die and decay, it’s released back into the skies and the oceans.

But human civilization has been pumping more carbon into the environment by burning carbon-rich fossil fuels like coal, oil, and natural gas. On the current trajectory, the oceans are expected to absorb at least another 300 billion tons of carbon by 2100 — an amount that could end up producing long-term changes to the environment, Rothman concluded.

Sedimentary rocks at Meishan, China contain signatures of a disturbance in the carbon cycle immediately preceding Earth's greatest mass extinction.

Passing the threshold Rothman has calculated could mean abrupt environmental change — abrupt in biological and geochemical terms meaning within 10,000 years, Rothman said.

“It’s not that the date 2100 is a magic date,” he said. “It’s that the projection of the amount of carbon that will have been added by anthropogenic means — fossil fuel burning — for the most part suggest that 300 gigaton limit will have been surpassed by end of the century. But it may happen sooner. The question in the end is: What happens next?”

The study was published Wednesday in the research journal Science Advances.

Rothman isn’t alone in warning of a potential extinction. Some scientists argue a sixth such event is under way already, with about two species a year disappearing and thousands seeing their populations and ranges shrink. And scientists have long warned that an increase in global average temperatures beyond 2 degrees Celsius (3.6 degrees Fahrenheit) could have catastrophic consequences.

Read more at Seeker