Mumbai’s Basalt Rocks Date Back to Volcanic Era Linked to Dinosaur Extinction

Around 66 million years ago, a roughly 10-kilometre-wide asteroid struck the Gulf of Mexico, driving more than 75 per cent of Earth’s species to extinction, including the dinosaurs. The impact created the Chicxulub crater on Mexico’s Yucatan Peninsula, a formation more than 110 miles wide. The collision struck with the force of billions of atomic bombs, triggering fires, tsunamis and climatic shifts.

At almost the same time, on the other side of the world, western India was experiencing one of the largest volcanic events in Earth’s history. The entire western tract of Maharashtra is built from basaltic lava flows known as the Deccan Traps, dated to around 67.4 million years ago. These layered flood basalts are more than 2,000 metres thick in places and cover about 500,000 square kilometres.

The close timing of the two events has intrigued scientists for years. In 2015, a team led by UC Berkeley researcher Mark Richards examined the “uncomfortably close” occurrence of the Chicxulub impact and the largest phase of the Deccan Traps eruptions, arguing that the timing was unlikely to be a coincidence.

The research found that the impact could have generated seismic energy dense enough to travel through the upper 200 kilometres of Earth’s mantle, potentially triggering volcanic eruptions worldwide. However, the same paper acknowledged that Deccan volcanism had already begun well before the asteroid impact, while a direct melting effect from Chicxulub could not by itself explain the coincidence. The hypothesis remains debated among geologists and has not been proven.

Mumbai’s own geology carries traces of this period. The city, made up of islands linked by land reclamation, is built predominantly on volcanic rock, with basalt exposed at sites such as Borivali in Sanjay Gandhi National Park. Nearby, the Elephanta Caves, carved from Deccan basalt, remain one of the best places near the city to see the ancient rock up close.

Whether the asteroid alone wiped out the dinosaurs or whether Deccan volcanism dealt a compounding blow remains an open question in palaeontology. What is settled is that Mumbai’s dark, layered rock is a direct physical remnant of one of the most consequential periods in the planet’s history.