Most mass extinctions began with vast convulsions of Earth’s interior—can we detect that?
“The revolutions and changes which have left the earth as we now find it, are not confined to the overthrow of the ancient layers” – Georges Cuvier, 1831.
Our planet Earth has extinguished large portions of its inhabitants several times since the dawn of animals. And if science tells us anything, it will surely try to kill us all again. Working in the 19th century, paleontology pioneer Georges Cuvier saw dramatic turnovers of life in the fossil record and likened them to the French Revolution, then still fresh in his memory.
Today, we refer to such events as “mass extinctions,” incidents in which many species of animals and plants died out in a geological instant. They are so profound and have such global reach that geological time itself is sliced up into periods—Permian, Triassic, Cretaceous—that are often defined by these mass extinctions.
Debate over what caused these factory resets of life has raged ever since Cuvier’s time. He considered them to be caused by environmental catastrophes that rearranged the oceans and continents. Since then, a host of explanations have been proposed, including diseases, galactic gamma rays, dark matter, and even methane from microbes. But since the 1970s, most scientists have considered the likely root cause to be either asteroid impacts, massive volcanic eruptions, or a combination of both.
Those asteroid (or comet) impacts have captured the public imagination ever since 1980, when Luis and Walter Alvarez found global traces of iridium, which they inferred to be extraterrestrial, at the geological boundary that marked the disappearance of the dinosaurs. The identification of the Chicxulub impact crater in Mexico soon after sealed the deal. Impacts have been proposed to explain other mass extinctions, but there’s very little actual evidence to support those links. In the words of researchers David Bond and Stephen Grasby, who reviewed the evidence in 2016: “Despite much searching, there remains only one confirmed example of a bolide impact coinciding with an extinction event.”
Not just a random series of unfortunate events
Volcanism, on the other hand, has coincided with most, if not all, mass extinctions—it looks suspiciously like a serial killer, if you like.
This isn’t your regular Vesuvius/St. Helens/Hawaii style volcanism. It’s not even super-volcanoes like Yellowstone or Tambora. I’m talking about something far, far bigger: a rare, epic volcanic phenomenon called a Large Igneous Province or “LIP.”
LIPs are floods of basalt lava on an unimaginable scale: the Siberian Traps LIP, which erupted at the end-Permian extinction, covers an area the size of Europe. It’s estimated that over 3 million cubic kilometers of rock were vomited onto the planet’s surface, The end-Triassic Central Atlantic Magmatic Province, stretching from Canada to Brazil into Europe and West Africa, was just as large. Others are similarly gigantic.
In the words of Bond and Grasby, “Four of the ‘Big Five’ extinctions are associated with LIPs—too many to be mere coincidence —implying that large-scale volcanism is the main driver of mass extinctions.”
Even the extinction of the dinosaurs at the end of the Cretaceous was simultaneous with the Deccan Traps LIP in India. It’s possible that the combination of the Chicxulub asteroid impact and the Deccan eruptions, rather than just the impact, pushed life over the edge. And recent evidence points to a LIP trigger for the second phase of the end-Ordovician extinction, the one missing from Bond and Grasby’s quote. If confirmed, that would link LIPs to all five of the Big Five extinctions.