For decades, scientists have pondered the hypothesis that mass extinctions do not happen randomly, but operate on a cycle of around 27 million years. Now a new study sheds more weight on this idea that mass extinctions of land animals, including amphibians, reptiles, mammals, and birds, occur once every 27 million years; after all, the end of Cretaceous event is only the most recent of these stages of global catastrophe on Earth.
Paleontologists recognize, in fact, five major mass extinction events in the fossil record:
- At the end of the Ordovician period , about 443 million years ago, in which it is estimated that 86% of all marine species disappeared.
- At the end of the Devonian period, about 360 million years ago, when 75% of all species became extinct
- At the end of the Permian period , about 250 million years ago, it represented the worst extinction event yet, with an extinction rate of 96%.
- At the end of the Triassic period, about 201 million years ago, when 80% of all species disappeared from the fossil record.
- At the end of the Cretaceous, about 65 million years ago, when 76% of all species became extinct, including the famous dinosaurs.
The study published in the journal Historical Biology also finds that these mass extinctions line up with major asteroid impacts and devastating volcanic eruptions.
American scientists performed statistical analyzes on the dates of 10 recognized mass extinction events that killed any tetrapod (animals with four limbs). They detected an underlying “statistically significant” frequency of mass extinctions in a similar cycle of approximately 27.5 million years. This data coincides with the fact that it is known that three of the massive killings of species on land and in the sea occurred at the same time as the three largest impacts of the last 250 million years , each capable of causing a global disaster. and lead to extinctions.
What causes these cycles?
If mass extinctions coincide with eruptions and massive asteroid impacts, the challenge now is to explain what mechanism could make these eruptions so regular, how they align with these rocky collisions from space.
Thus, astrophysicists hypothesize that periodic comet showers occur in the solar system every 26-30 million years, producing cyclical impacts and leading to periodic mass extinctions. And considering that the Sun and planets traverse the crowded mid-plane of the Milky Way approximately every 30 million years, during those times, comet showers are possible, causing large collisions on Earth.
“It appears that large-body impacts and pulses from Earth’s internal activity creating a flooded basalt volcanism may be marching at the same rate of 27 million years as extinctions, perhaps at the rate of our orbit on the Via Milky, -which unleashes showers of comets that have the potential to end all life on our planet- “said Michael Rampino, researcher in the Department of Biology at New York University and leader of the study.
Extinction triggers
Comet showers would cause major impacts on Earth, creating conditions that would stress and potentially kill terrestrial and marine life, as well as widespread darkness and cold, forest fires, acid rain and ozone depletion. Meanwhile, volcanic eruptions would cover vast areas with lava and create an environment very unsuitable for life, including brief periods of intense cold, ozone destruction and increased exposure to radiation, as well as acid rain.
When would the next event be?
The most recent mass extinction event referred to by the authors was 7.25 million years ago , suggesting that another such catastrophe will not occur for another 20 million years.
Referencia: Michael R. Rampino et al. A 27.5-My underlying periodicity detected in extinction episodes of non-marine tetrapods. Historical Biology, published online December 10, 2020; doi: 10.1080/08912963.2020.1849178
