Asteroids aren't completely random? Mass extinctions of Earth's land animals follow a cycle, study finds
Mass extinctions of life on Earth appear to follow a regular pattern, a new study suggests.
In fact, widespread die-offs of land-dwelling animals – which include amphibians, reptiles, mammals and birds – follow a cycle of about 27 million years, the study reports.
The study also said these mass extinctions coincide with major asteroid impacts and devastating volcanic outpourings of lava.
"The global mass extinctions were apparently caused by the largest cataclysmic impacts and massive volcanism, perhaps sometimes working in concert," said study lead author Michael Rampino of New York University, in a statement.
Paleontologists had previously discovered that similar mass extinctions of marine life, in which up to 90% of species disappeared, were not random events, but seemed to come in a 26-million-year cycle.
How could this be? Aren't asteroid or comet impacts completely random? Apparently not, the study suggests, and it's because of the orbit of our planet through the galaxy.
The solar system passes through the crowded part of our Milky Way galaxy about every 30 million years. During those times, comet showers are possible, leading to large impacts on the Earth.
"These new findings of coinciding, sudden mass extinctions on land and in the oceans, and of the common 26- to 27-million-year cycle, lend credence to the idea of periodic global catastrophic events as the triggers for the extinctions," Rampino said.
"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 said that the impacts can create conditions that would stress and potentially kill off land and marine life, including widespread dark and cold, wildfires, acid rain and ozone depletion. The most infamous asteroid strike we know of is the one that killed off the dinosaurs some 66 million years ago, which overall wiped out 70% of the species on Earth.
"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," Rampino said.
And as for where we are in the current cycle, he told USA TODAY that we're about 20 million years away from the next predicted mass extinction that's due to a comet strike or volcanic activity.
The study was published Friday in the journal Historical Biology.
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This article originally appeared on USA TODAY: Earth mass extinctions of life occur in 27-million-year cycles: Study
