Mass extinctions of land-dwelling animals — including amphibians, reptiles,
mammals, and birds — follow a cycle of about 27 million years, coinciding
with previously reported mass extinctions of ocean life, according to a new
analysis published in the journal Historical Biology.
The study also finds that these mass extinctions align with major asteroid
impacts and devastating volcanic outpourings of lava called flood-basalt
eruptions — providing potential causes for why the extinctions occurred.
“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.
Sixty-six million years ago, 70 percent of all species on land and in the
seas, including the dinosaurs, suddenly went extinct, in the disastrous
aftermath of the collision of a large asteroid or comet with the Earth.
Subsequently, paleontologists discovered that such mass extinctions of
marine life, in which up to 90 percent of species disappeared, were not
random events, but seemed to come in a 26-million-year cycle.
In their Historical Biology study, Rampino and co-authors Ken Caldeira of
the Carnegie Institution for Science and Yuhong Zhu of NYU’s Center for Data
Science, examined the record of mass extinctions of land-dwelling animals
and concluded that they coincided with the extinctions of ocean life. They
also performed new statistical analyses of the extinctions of land species
and demonstrated that those events followed a similar cycle of about 27.5
million years.
What could be causing the periodic mass extinctions on land and in the seas?
Mass extinctions are not the only events occurring in cycles: the ages of
impact craters — created by asteroids and comets crashing to the Earth’s
surface — also follow a cycle aligning with the extinction cycle.
Astrophysicists hypothesize that periodic comet showers occur in the Solar
System every 26 to 30 million years, producing cyclical impacts and
resulting in periodic mass extinctions. The Sun and planets cycle through
the crowded mid-plane of the Milky Way Galaxy about every 30 million years.
During those times, comet showers are possible, leading to large impacts on
the Earth. 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.
“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,” said Rampino. “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 researchers were surprised to find another possible explanation beyond
asteroids for mass extinctions: flood-basalt eruptions, or giant volcanic
eruptions that cover vast areas with lava. All eight of the coinciding mass
die-offs on land and in the oceans matched times of flood-basalt eruptions.
These eruptions also would have created severe conditions for life,
including brief periods of intense cold, acid rain, and ozone destruction
and increased radiation; longer term, eruptions could lead to lethal
greenhouse heating and more acid and less oxygen in the ocean.
“The global mass extinctions were apparently caused by the largest
cataclysmic impacts and massive volcanism, perhaps sometimes working in
concert,” added Rampino.
Reference:
A 27.5-My underlying periodicity detected in extinction episodes of
non-marine tetrapods
Michael R. Rampino ,Ken Caldeira &Yuhong Zhu
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