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11 Dec, 2020 13:50

Global mass extinctions follow regular 27-million-year cycle, may be linked to Earth’s journey through Milky Way

Global mass extinctions follow regular 27-million-year cycle, may be linked to Earth’s journey through Milky Way

Researchers at New York University have discovered that mass extinction events throughout Earth’s history have an underlying cycle of roughly 27 million years, which may be tied to the planet’s path through the galaxy.

Mass extinction events affecting land-dwelling animals from mammals and birds to amphibians and reptiles have occurred numerous times throughout our planet’s history, but the researchers concentrated on 10 distinct episodes of intensified extinctions over the past 300 million years.

Their new analysis, published in the journal Historical Biology, finds that mass extinction events closely align with asteroid impacts and increased volcanic activity in the form of flood-basalt eruptions.

“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,” said Michael Rampino, a professor in New York University’s Department of Biology and the study’s lead author.

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Scientists have long studied the mass extinction event roughly 66 million years ago, during which some 70 percent of all species disappeared from the face of the Earth.

Similar mass extinctions in the world’s oceans also appeared to follow a similar, though slightly shorter, pattern. 

Rampino and his colleagues pored over troves of paleontological data and realized there was a strong correlation between the mass extinction events on land and in the seas. 

The land-based extinction events appeared to reoccur in 27.5-million-year cycles while the oceanic events followed a 26-million-year cycle. 

Impact craters from asteroids and comets striking Earth also appear to follow a pattern that aligns with this 26- to 30-million-year extinction cycle. 

Astrophysicists suspect these great die-offs may occur when the solar system passes through the particularly crowded mid-plane of the Milky Way, at which point the Earth is subjected to more cosmic violence than normal. 

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During these periods, comet showers become more frequent, increasing the likelihood of Earth impact which, in turn, triggers periods of dark and cold caused by vast dust clouds, as well as other threats to life such as wildfires, acid rain, ozone depletion and acidification of the oceans. 

“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,” Rampino said.

Curiously, eight of the mass die-offs closely studied by the researchers also coincided with flood-basalt eruptions which would also have created planetary conditions that are toxic for many forms of life through an accelerated greenhouse effect which increases acidity in the world’s oceans while reducing oxygen content. 

“The global mass extinctions were apparently caused by the largest cataclysmic impacts and massive volcanism, perhaps sometimes working in concert,” Rampino added.

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