Earth's greatest crime scene
Around 66 million years ago, western India was torn apart by one of the largest volcanic events in Earth's history. Over hundreds of thousands of years, fissure eruptions unleashed a staggering volume of basaltic lava, which today covers 500,000 square kilometers (200,000 sq mi). Originally, the lava may have covered 1.5 million square kilometers, an area half the size of modern India. The accumulated layers of solidified lava are in some places more than 2 kilometers (1.2 miles) thick, forming the step-like landscape that gives the Deccan Traps their name. The total volume of erupted material is estimated at 1 million cubic kilometers (240,000 cu mi).
This colossal outpouring of lava occurred in several pulses. High-precision dating using zircon crystals found in ash layers between the lava flows reveals the main eruptive phase began about 250,000 years before the mass extinction event. This phase, which accounted for about 80-90% of the total lava volume, continued for 750,000 years. The eruptions spewed immense quantities of sulfur dioxide and carbon dioxide into the atmosphere, causing climate shifts. The sulfurous gases likely caused a drop in global temperatures by about 2°C, leading to a "volcanic winter," while the carbon dioxide drove long-term greenhouse warming and ocean acidification.
Prime suspect or accomplice?
The timing of this immense volcanic event and the Chicxulub asteroid impact is, geologically speaking, simultaneous. For decades, scientists have debated which catastrophe was the primary killer in the end-Cretaceous mass extinction. The impact of a 10-kilometer-wide asteroid would have created an "impact winter" by throwing dust and aerosols into the atmosphere, blocking sunlight. The Deccan eruptions were slower, more prolonged planetary stressor, poisoning the atmosphere and oceans over millennia.
One hypothesis suggests the two events are causally linked. The seismic shock from the Chicxulub impact—estimated to be equivalent to a magnitude 9 earthquake or larger everywhere on Earth—could have intensified the ongoing volcanism in India. Evidence suggests that about 70% of the Deccan Traps' lava volume erupted within 100,000 years of the impact. This theory proposes that the impact's seismic waves increased the permeability of the Earth's mantle, allowing vast quantities of already-present magma to surge to the surface. This would have turned a persistent volcanic problem into an acute, world-ending cataclysm, delivering the final blow to the already-stressed ecosystems and the non-avian dinosaurs.