Kate Lunau, writing for Motherboard: A new paper in Science Advances finds that a mass extinction period mirroring ones from our planet's ancient past could be triggered when humanity adds a certain amount of carbon to the oceans, which are home to the majority of all plants and animals on our planet. The paper pegs that amount at 310 gigatons. According to lead author Daniel Rothman of MIT, based on projections from the Intergovernmental Panel on Climate Change, we're on course to hit that number by 2100. After that, we enter "unknown territory." [...] Previous mass extinctions have happened over the course of thousands or millions of years, but the period of change we're in right now has lasted centuries at best, making it hard to compare them. Although plenty of experts say Earth is already experiencing a sixth mass extinction, that remains "a scientific question," Rothman, who is professor of geophysics in the MIT Department of Earth, Atmospheric and Planetary Sciences, told me. Once our planet hits the threshold he identified in this paper, he explained, it will kickstart changes that will "amplify" everything that came before. These same changes, to reiterate, have been associated with all previous mass extinctions on Earth.