The second suspect
Around 66 million years ago, as non-avian dinosaurs entered their final act, the Indian subcontinent was an island drifting north. It passed over the Réunion hotspot, a mantle plume that triggered one of the largest volcanic events in Earth's history. For thousands of years, fissure eruptions poured out basaltic lava, eventually covering 500,000 square kilometers of land in layers up to 2 kilometers thick. This immense volcanic province is known as the Deccan Traps.
The sheer volume of these eruptions released climate-altering gases. Estimates suggest the volcanoes pumped as much as 10.4 trillion tons of carbon dioxide and 9.3 trillion tons of sulfur into the atmosphere. This would have caused intense acid rain and wild temperature swings, from initial cooling due to sulfur aerosols to long-term warming from carbon dioxide. The main phase of the eruption began just before the Chicxulub asteroid impact, making it a suspect, or at least a major accomplice, in the end-Cretaceous mass extinction.
Life between the flows
The Deccan Traps were not a single event but a series of pulses. Between eruptions, life returned to the barren volcanic plains. Sediments washed into lakes and rivers, creating layers of mudstone, siltstone, and sand between the hardened basalt flows. These "intertrappean beds" contain fossils, recording the ecosystems that existed during the volcanic chaos.
These beds contain a surprising diversity of fossils. There are freshwater mollusks, ostracods (seed shrimp), and the remains of fish and turtles. Plant fossils, including palms and ferns, show that tropical forests grew on the temporary landscapes. One of the most significant finds is the toothed frog Indobatrachus, a representative of an early frog lineage with relatives in Australia, pointing to the ancient Gondwanan connection of the Indian landmass. Even dinosaur remains, including eggs and bone fragments, appear in the layers just below and between the earliest lava flows, showing they lived in this volcanic world right up to the extinction boundary.
The basalt rock of the Deccan Traps eventually weathered into a dark, fertile soil called regur. Today, this soil makes the region a productive agricultural area. The stepped, canyon-like topography created by the lava flows also forms the Western Ghats, a mountain range recognized as a biodiversity hotspot. This area hosts hundreds of endemic species, including the four-horned antelope (Tetracerus quadricornis), the Indian giant squirrel (Ratufa indica), and the Jerdon's courser (Rhinoptilus bitorquatus), a bird once thought to be extinct. The ancient lava flows that witnessed the end of one era became the foundation for the unique biodiversity of another.