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After analysing the records of mass extinction events of land animals, scientists have said that these events typically follow a cycle of about 27m years.
While not exactly precise, scientists in the US claim that the mass extinctions of land-dwelling animals have followed a rather regular cycle. In a new study published to Historical Biology, a team led by researchers at New York University found that these events occur about every 27m years, coinciding with previously reported mass extinction events of ocean life.
The study also found that these mass extinctions align with major asteroid impacts and volcanic outpourings of lava called 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 27m-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.
Around 66m years ago, 70pc of all species – both on land and sea – went extinct following the collision of a massive asteroid with the Earth, ending the dinosaur age. Subsequently, palaeontologists discovered that such mass extinctions of marine life – in which up to 90pc of species disappeared – were not random events, but seemed to come in a 26m-year cycle.
As part of this new study, the research team examined the records of mass extinctions of land animals and concluded that they coincided with the extinction of ocean life. It also performed new statistical analyses of the extinctions of land species and demonstrated that those events followed a similar cycle of about 27.5m years.
Possible explanations
“These new findings of coinciding, sudden mass extinctions on land and in the oceans, and of the common 26- to 27m-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 250m years, each capable of causing a global disaster and resulting mass extinctions.”
One possible explanation for these events is the periodic comet showers that occur in the solar system every 26m to 30m years. However, the team was surprised to find that giant volcanic eruptions could also be a possible explanation, as all eight of the coinciding mass die-offs matched times with such eruptions.
These events would have created severe conditions for life on Earth, including brief periods of intense cold, acid rain, ozone destruction and increased radiation.
Rampino said: “The global mass extinctions were apparently caused by the largest cataclysmic impacts and massive volcanism, perhaps sometimes working in concert.”
