Volcanic Winters May Have Weakened Dinosaurs Prior Extinction Due to Asteroid Blast, Study Suggests

Since the discovery of a 65-million-year-old impact crater below the Gulf of Mexico, experts have debated whether massive volcanic eruptions or the impact of the asteroid alone is most responsible for the demise of dinosaurs. A collaborative study entitled "Recurring volcanic winters during the latest Cretaceous: Sulfur and fluorine budgets of Deccan Traps lavas" suggests that before their eventual extinctions, these giant reptiles might have faced repeated "volcanic winters."

What is Volcanic Winter?

Volcanic winter refers to reducing global temperatures due to massive amounts of volcanic ash and sulfur aerosols deposition in the Earth's atmosphere. It is believed that this phenomenon has occurred several times throughout Earth's history, with varying degrees of severity.

Sulfur aerosols reflect incoming solar radiation and absorb land radiation, causing the troposphere to cool down. Enough loading of these droplets can result in climate changes at the global scale for years after the event. Long-term effects include crop failures, cooler temperatures, and unusual weather conditions across the planet.

Investigating Deccan Traps Volcanism

To answer whether volcanic eruptions had a role in the extinction of dinosaurs, an international team of scientists from the US, Canada, Norway, and Italy have looked at the environmental impact of the Deccan Traps eruptions. This feature is a large igneous province in west-central India, which takes the form of a large shield volcano.

The Deccan Traps began forming at the end of the Cretaceous period, about 66.25 million years ago. Its formation could have been triggered by the bulk of volcanic eruptions at India's Western Ghats mountain range between 66 and 65 million years ago.

The research team analyzed trapped sulfur and fluorine compounds in samples obtained from the lava pile in the Western Ghats. Led by geologist Don Baker, the experts determined the minute concentrations of the compounds through synchrotron radiation X-ray fluorescence spectrometry. They also estimated the sulfur and fluorine compounds that had flooded the atmosphere during the Cretaceous period.

The analysis revealed that the sulfur and fluorine released by the Deccan Traps 200,000 years before the extinction-level event likely dropped global temperatures as much as 18 degrees Fahrenheit (10 degrees Celsius). A steady drop in temperature during the late Cretaceous period coincided with higher concentrations of sulfur compounds in several layers of ancient lava from the Deccan Traps.

In these layers, sulfur content was as high as 1,800 parts per million. The team's calculations also indicate that a volume of sulfur gas measuring between 20,000 and 112,000 cubic miles (86,000 and 466,000 cubic kilometers) erupted into the prehistoric atmosphere. Meanwhile, fluorine gasses may not majorly contribute to climate change, but their concentrations have other local, toxic effects.

From these findings, Baker and his colleagues assumed that Deccan Trap volcanism set the stage for a global biotic crisis. The instability of climatic conditions would have made life difficult for all ancient plants and animals, weakening the dinosaur before the final blow from the asteroid impact. The study highlights the intricate connections between environmental factors that led to one of history's most significant extinction events.

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