Mass extinctions of Earth’s animals have occurred every 27 million years, a new study has found — suggesting that these events are not as random as we thought.
And according to the cyclic pattern, we’re currently about 20 million years away from the next predicted mass extinction. (That’s, of course, if climate change doesn’t wipe us out sooner.)
The extinction of land-dwelling animals — including amphibians, reptiles, mammals, and birds — follows a cycle of about 27 million years, a pattern that coincides with previously reported mass extinctions of ocean life, according to a new analysis published in the journal Historical Biology.
The researchers compared the timing of recorded extinction events with the age of impact craters formed by asteroids and comets crashing into the planet’s surface, and found that they often coincided; these impacts led to widespread dark and cold conditions due to crash debris blocking the sun’s rays, and also caused wildfires, acid rain, ozone depletion, and other effects that jeopardized the existence of both terrestrial and marine life. One of the most well-known asteroid strikes occurred 66 million years ago and wiped out 70% of the Earth’s species.
The team also matched the timing of mass extinctions with that of flood basalts, giant volcanic eruptions that flood large areas with lava and also cause lethal greenhouse heating (due to the massive release of carbon dioxide and methane into the atmosphere), anoxia and acidification of oceans, and the potential release of poisonous gases from the anoxic oceans.
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“These new findings of coinciding, sudden mass extinctions on land and in the oceans … lend credence to the idea of periodic global catastrophic events as the triggers for the extinctions. In fact, three of the mass annihilations of species on land and in the sea are already known to have occurred at the same times as the three largest impacts of the last 250 million years, each capable of causing a global disaster and resulting mass extinctions,” the study’s lead author Professor Michael Rampino, from the department of biology at New York University, told the media.
“It seems that large-body impacts and the pulses of internal Earth activity that create flood-basalt volcanism may be marching to the same 27-million-year drumbeat as the extinctions, perhaps paced by our orbit in the galaxy,” Professor Rampino added in his statement to USA Today.
The researchers do have a hypothesis to explain why the pattern appears to repeat itself. The solar system passes through a crowded part of the Milky Way galaxy every 30 million years or so — facilitating the attraction of large space objects into Earth’s orbit and setting them on a collision course. Further, the team suggests that while volcanic eruptions are, generally, perceived to be the result of Earth’s internal dynamics, they could also be related to astrophysical factors that get triggered periodically as the Earth traverses the universe.
