Research Outcome

About 252 million years ago, the largest mass extinction and the largest volcanic eruptions in Earth history occurred apparently synchronously:

  • Worldwide 90% of marine species and 70% of terrestrial species went extinct.
  • In Siberia 6,000,000 cubic kilometers of magma erupted, enough to cover the continental U.S. to almost a mile in depth.

What caused the eruption? What caused the extinction? Were they linked? Over the past nine years, my colleagues and I have made eight trips to central Siberia to investigate this apparent coincidence.

We can count the causes of global extinctions on less than one hand: giant meteoroid impact, nuclear war, and chemical change of the atmosphere. That’s about it. At the end-Permian there is no geological evidence of a major meteoroid impact: no ash layer, no iridium enrichment from space material, no crater, no layers of spheres of scattered and fallen melt from impact. We can pretty safely assume there was no nuclear war at the end-Permian. That leaves us with a chemical change of the atmosphere.

Eruption: But How Big?

A volcanic eruption can certainly chemically change the atmosphere, but for years, many experts were skeptical about whether flood basalts could do that. Flood basalts lie somewhat outside the plate tectonic paradigm — most of the volcanoes on Earth today lie along plate boundaries, either where new plates are being formed (mid-ocean ridges) or where one is sinking down beneath another (for example, Japan). Flood basalts occur in the middle of plates. Though there are no flood basalts erupting on Earth today, we see the many thin layers of lava of past eruptions in a number of places around the world.

These aren’t explosive eruptions like Mt. St. Helens or Pinatubo. Instead, the runny lavas flood out of fissures to spread across the countryside. Though several seem to have coincided in time with extinction events, many others did not. Furthermore, flood basalts did not seem to carry the kinds of climate-changing gases and the explosive ability to launch those gases into the stratosphere that are needed to change global climate.

But our research team thought that the Siberian flood basalts had something to do with the extinction. Henrik Svensen and Sverre Planke at the University of Oslo discovered that the magmas heated the rocks they passed through on the way to eruption, and those heated rocks gave off climate-changing gases. We wondered whether the magmas themselves had carried enough gases to change the climate.

Climate-Changing Gases

Along with the carbon and sulfur, which we had expected, we found that the magmas carried surprisingly high levels of fluorine and chlorine. These levels could not have come from melting in the Earth’s mantle; they had to come (as we subsequently proved) from the sedimentary rocks and hydrocarbon reservoirs that the magmas traveled through and rested in on their way to the surface.

Thus these normally quiet flood basalt lavas carried and released a world of trouble into the end-Permian atmosphere. And that trouble came in the form of halocarbons, the same family of chemicals now banned by international treaties because they were destroying our ozone layer. Work by Ben Black, Jeff Kiehl, Jean-Francois Lamarque, and Christine Shields at the National Center for Atmospheric Research showed that the halocarbons released by the Siberian flood basalts would have destroyed as much as 70 percent of the Earth’s ozone, worldwide. And the sulfur compounds would have made rain in the northern hemisphere as acidic as lemon juice.

A Question of Timing

Finally, we had to demonstrate that the eruption and extinction were truly related in time. We set out to improve the date measurements and demonstrate that the volcanic eruptions began, and then the extinction happened. If the extinction happened first — well, we are pretty sure that extinctions don’t cause volcanoes, so we would have been left with an astounding coincidence. Though this simple sentence cannot do justice to the many years of effort it took, Seth Burgess and Sam Bowring of MIT have now definitively shown that the eruptions completed a majority of their volume before the extinction occurred.

We now know that the Siberian flood basalts did cause the end-Permian extinction, though changing atmospheric chemistry with the same chemicals that humankind is releasing into the atmosphere today. Along the way to this new knowledge we trained many young scientists, we created strong and lasting ties among scientists in eight different countries and across many disciplines, and we helped produce a film that was shown on the Smithsonian Channel, along with many pieces of popular writing in several different languages. Thus the fundamental scientific research became a source for strong friendships across nationals, and of broader education.