Recently paleontologists have discovered something that many will find rather chilling. According to new research, mass extinctions of land-dwelling animals, including amphibians, reptiles, mammals, and birds, follow a cycle spanning about 27 million years. Interestingly, this mass extinction cycle also coincides with previously reported mass extinctions of ocean life. The study has found that mass extinctions align with significant asteroid impacts and volcanic eruptions on Earth.
There are five major mass extinction events in the fossil record. Those mass extinctions include one at the end of the Ordovician period 443 million years ago, one at the end of the Denovian period 360 million years ago, one at the end of the Permian period 250 million years ago, one at the end of the Triassic period 201 million years ago, and one at the end of the Cretaceous period 65 million years ago.
Other minor extinction events have happened over the eons. Statistical analysis performed during the study of the extinction of land species suggests the events following a cycle of every 27.5 million years. Authors of the study compared the ages of extinction events with ages of impact craters created by asteroids and comets impacting the Earth or massive volcanic eruptions or series of eruptions that cover large areas of land and lava and emitted greenhouse gases into the atmosphere.
Researchers on the study say that the new findings lend credence to the idea of periodic global catastrophic events as triggers for extinctions. Aside from asteroid and comet impacts, researchers also suggest that mass extinctions on land and the oceans also matched the time of flood-basalt eruptions. These last several millennia releasing toxic gases into the atmosphere leading to extreme warming and gases being washed into the sea, acidifying the ocean.
The study offers no conclusive explanation of what controls the periodic mass extinction events. One controversial theory is that a companion star to the Sun in a massive orbit might stir comets, throwing them at the Earth every 26 million years. Flood-basalt eruptions every 25 to 30 million years could result from long-term cycles of plumes rising in the Earth’s mantle.