Determining what killed the dinosaurs 66 million years ago at the end of the Cretaceous Period has been a topic of debate for a long time.
Some scientists think comets are the most likely cause of mass destruction, while others think volcanic eruptions were the cause. The key driver of mass extinctions may have been volcanic activity, according to a new study.
It is clear from the findings that the link between major volcanic eruptions and wholesale species turnover is not a matter of chance.
The researchers say that four of the mass extinctions are related to a volcanic eruption. lava in the blink of a geological eye floods vast areas, even an entire continent. They leave behind giant fingerprints that show the presence of large igneous provinces.
To be considered a large province, it must have at least 100,000 km of magma. The eruption of Mount St. Helens involved less than a kilometer of molten rock. Most of the volcanoes in the study erupted on a million times more lava than that, according to the researchers.
The temporal connection between mass extinction and large igneous provinces was examined by the team.
"The large step-like areas of igneous rock from these big volcanic eruptions seem to line up in time with mass extinctions and other significant environmental events," says lead author Theodore Green, who is now a graduate student.
A series of eruptions in Siberia triggered the most destructive mass extinctions in history, releasing a huge pulse of carbon dioxide into the atmosphere. The largest region of volcanic rock in the world is called the Siberia Traps.
Around the time of the great dinosaur die-off, volcanic eruptions in India created the Deccan plateau. This would have had far-reaching global effects, blanketing the atmosphere in dust and toxic fumes, as well as altering the climate on long time scales.
The theories in favor of asteroid impact are based on the fact that the dinosaurs went extinct at the same time as the Chicxulub impactor.
When the impact crater was discovered, all other theories about the death of the dinosaurs were thrown out the window. There isn't much evidence of similar impact events that coincide with the other mass extinctions.
Green set out to find a way to quantify the apparent link between eruptions and extinctions and see if there was evidence of a causality between the two. Green recruited the supercomputers at the Dartmouth Discovery Cluster to crunch the numbers for the book.
The estimates of flood basalt eruptions were compared with periods of extinctions in the geological timescale. They looked at whether the eruptions would line up just as well with a randomly generated pattern if they repeated the exercise with 100 million such patterns. The agreement with extinction periods was more likely than random chance.
Our results make it hard to ignore the role of volcanism in extinction because it is difficult to determine if a particular volcanic eruption caused one particular mass extinction. The correlation between volcanic basalt floods and mass extinctions has not been observed.
The research team ordered the volcanic events based on the rate at which they released lava. The volcanic events with the highest eruptive rates caused the most destruction.
The results show that there would have been a mass extinction regardless of whether there was an impact or not. Things were made worse by the impact.
The numbers were run for asteroids as well. When the Chicxulub impactor was not considered, the coincidence of impacts with periods of species turnover was weakened even more.
The Deccan Traps in India show that the stage was set for widespread extinction even without an asteroid. He says the impact sounded the death knell for the dinosaurs.
Flood basalt eruptions are rare in the geologic record. About 16 million years ago in the Pacific Northwest, there was a large scale event.
"While the total amount of carbon dioxide being released into the atmosphere in modern climate change is still very much smaller than the amount emitted by a large igneous province, fortunately, we're emitting it very fast, which is reason to be concerned." According to Green, carbon dioxide emissions are similar to the rate of flood basalts. He says that this places climate change in the framework of environmental catastrophes.
More information: Theodore Green et al, Continental flood basalts drive Phanerozoic extinctions, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2120441119. Journal information: Proceedings of the National Academy of Sciences
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