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How Dark Matter Could Have Helped Kill the Dinosaurs

The Milky Way’s galactic disc is a death trap, and guess what? We’re in it right now.
​The Milky Way. Image: ESO/S. Brunier

For decades, researchers have observed a bizarre pattern in the fossil record. Every 26 to 30 million years or so, extinction rates accelerate, with impacts and geothermal activity often to blame for the sudden biodiversity losses.

Interestingly enough, these catastrophes often correlate with the solar system's passage through the Milky Way's galactic disc, leading many scientists to speculate that the two cycles are related. For example, there is a widespread theory that the disc's tidal forces redirects Oort Cloud comets into the inner solar system, thus increasing deadly impacts. The timing of these periodic bombardments syncs up with major extinction events, including the one that killed off the dinosaurs 66 million years ago.

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Now, it turns out that there is another fascinating wrinkle to this repeating, galactic death trap: dark matter. This mysterious form of subatomic matter is thought to account for a quarter of the universe's mass, but it is observable only via its gravitational effects. And according to a study published today in the Monthly Notices of the Royal Astronomical Society, it might contribute the eerily cyclic destruction of life on Earth.

The Sun's location in the Milky Way. Image: NASA

For one thing, dark matter could exacerbate the tidal forces of the disc's visible matter. "The dark matter (and visible matter) in the disc gravitationally disturb the Oort Cloud of comets at the extreme edge of the solar system, and some fall inward towards the Sun," study author Michael Rampino, a biologist based at New York University, told me over email.

This might explain why impacts seem to increase during Earth's passage through the disc, but what about the uptick in geothermal activity every 30 million years? As it happens, dark matter might be behind that effect as well.

"Dark matter particles can pass into the Earth with no problem since they interact very weakly with ordinary matter," Rampino said. "Once [dark matter] is gravitationally captured, it loses energy and falls to the center of the Earth."

"The [dark matter] particles can become concentrated enough so that they annihilate each other, and this creates an extra source of heat that can cause change in the circulation of the core, and cause plumes of hot rock to rise from the core-mantle boundary," he continued. "This would happen preferentially during the disc crossing."

The craziest part of all of this is that the solar system is currently passing through this cosmic danger zone. "The last time we were at the mid-disc position was only three [million years ago], so we are essentially there now," Rampino said. "Several scientists have suggested that we are at present in a comet shower."

But before we panic in the face of an impending Dark Matter Doomsday scenario, scientists must collect more evidence that this correlation actually exists. "We need to discover and accurately date more impact craters on the the Earth to see if impacts really follow the cycles," Rampino said.

"We can also use the composition of the melted rock at an impact site to determine whether the impactors were asteroids or comets," he continued. "Better dating for all the geologic events would help test the hypothesis."

It is somewhat disquieting to accept that we're traversing through a disc that might make comet orbits go haywire, or force the Earth to burp up its molten contents. Galactic living offers some beautiful vistas, but as with every other structure in the universe, it is apparently not without apocalyptic trappings.