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Every once in a great while, something almost unspeakable happens to Earth. Some terrible force reaches out and tears the tree of life limb from limb. In a geological instant, countless creatures perish and entire lineages simply cease to exist.

The most famous of these mass extinctions happened about 66 million years ago, when the dinosaurs died out in the planet-wide environmental disruption that followed a mountain-sized space rock walloping Earth. We can still see the scar from the impact today as a nearly 200-kilometer-wide crater in the Yucatan Peninsula.

But this is only one of the “Big Five” cataclysmic mass extinctions recognized by paleontologists, and not even the worst. Some 252 million years ago, the Permian-Triassic mass extinction wiped out an estimated nine of every ten species on the planet—scientists call this one “the Great Dying.” In addition to the Big Five, evidence exists for dozens of other mass extinction events that were smaller and less severe. Not all of these are conclusively related to giant impacts; some are linked instead to enormous upticks in volcanic activity worldwide that caused dramatic, disruptive climate change and habitat loss. Researchers suspect that many—perhaps most—mass extinctions come about through the stresses caused by overlapping events, such as a giant impact paired with an erupting supervolcano. Maybe the worst mass extinctions are simply matters of poor timing, cases of planetary bad luck.

Or maybe mass extinctions are not matters of chaotic chance at all. Perhaps they are in fact predictable and certain, like clockwork. Some researchers have speculated as much because of curious patterns they perceive in giant impacts, volcanic activity and biodiversity declines.

In the early 1980s, the University of Chicago paleontologists David Raup and Jack Sepkoski found evidence for a 26-million-year pattern of mass extinction in the fossil record since the Great Dying of the Permian-Triassic. This 26-million-year periodicity overlaps and closely aligns with the Big Five extinctions, as well as several others. In subsequent work over the years, several other researchers examining Earth’s geological record have replicated Raup and Sepkoski’s original conclusions, finding a mass-extinction periodicity of roughly 30 million years that extends back half a billion years. Some of those same researchers have also claimed to detect similar, aligned periodicities in impact cratering and in volcanic activity. Every 30 million years, give or take a few million, it seems the stars align to make all life on Earth suffer. Yet for want of a clear mechanism linking all these different phenomena together, the idea has languished for years at the scientific fringe.

It may not be a fringe idea much longer. According to a new theory from Michael Rampino, a geoscientist at New York University, dark matter may be the missing link—the mechanism behind Earth’s mysterious multi-million-year cycles of giant impacts, massive volcanism and planetary death.

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