It took only 60,000 years to kill more than 90 percent of all life on Earth, according to the most precise study yet of the Permian mass extinction, the greatest die-off in the past 540 million years.
The new timeline doesn't reveal the culprit behind the die-off, though scientists have several suspects, such as volcanic eruptions in Siberia that belched massive quantities of climate-changing gases. But pinning down the duration of the Permian mass extinction will help researchers refine its potential trigger mechanisms, said Seth Burgess, lead study author and a geochemist at MIT.
Radioactivity and extinctions
The Permian mass extinction marks the end of the Permian geologic period, which ended approximately 252 million years ago. More than 96 percent of marine life and 70 percent of land species perished. By comparison, 85 percent of life died off during the dinosaur-killing extinction at the end of the Cretaceous period, 66 million years ago.
The best record of the Permian "great dying" is in Meishan, China. In past decades, hundreds of geologists collected and analyzed rocks in Meishan that date from before, during and after the Permian extinction. Researchers analyzed these rocks to better understand what caused the Permian event. Volcanic ash beds interlaced with Meishan marine rocks have tiny minerals called zircons that can be precisely dated.
Burgess and his co-authors improved the Meishan rock ages with the latest high-resolution, uranium-lead zircon dating techniques. Zircon traps minute amounts of naturally occurring radioactive uranium inside its crystal structure. Uranium decays into lead, and counting the ratio of the two elements provides an age estimate for the zircons.
The new dates show that the mass extinction started 251.941 million years ago (plus or minus 37,000 years) and ended at 251.880 million years ago (plus or minus 31,000 thousand years). The extinction's end also marks the start of the Triassic period, and coincides with the first fossil appearance at Meishan of a toothy, eel-like creature called Hindeodus parvus (a conodont, the source of the earliest teeth found in the fossil record).
Finding the killer(s)
The new timeline also provides greater accuracy for the environmental blows linked with the mass dying. For example, previous work has found an increase in carbon dioxide, a greenhouse gas, before the mass extinction began. In the Permian rocks, atmospheric carbon dioxide shifts are recorded as changes in the ratio of carbon isotopes.
The new study suggests the increase in carbon dioxide was sudden and short-lived, Burgess said. "It precedes the extinction by 20,000 years or so, and lasts 10,000 or 15,000 years. It was very short-duration event," he said.
But there are other potential tipping points for extinction beyond atmospheric greenhouse gases. For example, sea surface temperatures also rose about 10 degrees. And the sudden carbon dioxide increase may have made the oceans more acidic.
60,000 Years to Kill Nearly Everything