What killed dinosaurs’ life on Earth

Determining what killed the dinosaurs 66 million years ago at the end of the Cretaceous Period has long been the topic of debate, as scientists set out to determine what caused the five mass extinction events that reshaped life on planet Earth in a geological instant. Some scientists argue that comets or asteroids that crashed into Earth were the most likely agents of mass destruction, while others argue that large volcanic eruptions were the cause.

A new Dartmouth-led study published in the Proceedings of the National Academy of Sciences (PNAS) reports that volcanic activity appears to have been the key driver of mass extinctions. The findings provide the most compelling quantitative evidence so far that the link between major volcanic eruptions and wholesale species turnover is not simply a matter of chance.

Four of the five mass extinctions are contemporaneous with a type of volcanic outpouring called a flood basalt, the researchers say. These eruptions flood vast areas—even an entire continent—with lava in the blink of a geological eye, a mere million years. They leave behind giant fingerprints as evidence—extensive regions of step-like, igneous rock (solidified from the erupted lava) that geologists call “large igneous provinces.”

To count as “large,” a large igneous province must contain at least 100,000 cubic kilometers of magma. For context, the 1980 eruption of Mount St. Helens involved less than one cubic kilometer of magma. The researchers say that most of the volcanoes represented in the study erupted on the order of a million times more lava than that.

The team drew on three well-established datasets on geologic time scale, paleobiology, and large igneous provinces to examine the temporal connection between mass extinction and large igneous provinces.

“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 climatic and environmental events,”says lead author Theodore Green ‘21, who conducted this research as part of the Senior Fellowship program at Dartmouth and is now a graduate student at Princeton.

In fact, a series of eruptions in present-day Siberia triggered the most destructive of the mass extinctions about 252 million years ago, releasing a gigantic pulse of carbon dioxide into the atmosphere and nearly choking off all life. Bearing witness are the Siberian Traps, a large region of volcanic rock roughly the size of Australia.

Volcanic eruptions also rocked the Indian subcontinent around the time of the great dinosaur die-off, creating what is known today as the Deccan plateau. This, much like the asteroid strike, would have had far-reaching global effects, blanketing the atmosphere in dust and toxic fumes, asphyxiating dinosaurs and other life in addition to altering the climate on long time scales.

On the other hand, the researchers say, the theories in favor of annihilation by asteroid impact hinge upon the Chicxulub impactor, a space rock that crash-landed into Mexico’s Yucatan Peninsula around the same time that the dinosaurs went extinct.

Science Daily