Mumbai's skyline stands atop Deccan Trap basalt formed during one of Earth's largest volcanic episodes, which occurred around the same time as the asteroid impact linked to the extinction of the dinosaurs.
According to an old report by Science, around 66 million years ago, a roughly 10-kilometre-wide asteroid struck the Gulf of Mexico, driving over 75% of Earth's species to extinction, including the dinosaurs. The strike formed the Chicxulub crater on Mexico's Yucatan Peninsula, a formation more than 110 miles wide, and it struck with the force of billions of atomic bombs, triggering fires, tsunamis and climatic shifts.
According to another research published in ScienceDirect titled Deccan Traps, at almost the same time, on the other side of the world, western India was in the grip of 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, and these layered flood basalts are more than 2,000 metres thick in places, covering some 500,000 square kilometres.
According to a report by Geological Society of America, the closeness of the timing 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, and argued this was unlikely to be coincidence. The paper found that the impact could have generated seismic energy dense enough to reach through the upper 200 kilometres of Earth's mantle, potentially enough to trigger volcanic eruptions worldwide. Crucially though, the same paper acknowledged that Deccan volcanism was already under way well before the impact, and that a direct melting effect from Chicxulub could not by itself explain the coincidence. The hypothesis remains debated among geologists and has not been proven.
According to GeoExpro Magazine, Mumbai's own geology bears the traces of this era. 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 this 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.
