There are a number of scientists who disbelive the theory that an asteroid impact killed the dinosaurs. They point to evidence that some species of sauropod may have survived the Chicxulub impact—widely hailed as the smoking gun in the dinosaur extinction—as proof that the event was simply not big enough to be a knockout blow. Now, according to Sankar Chatterjee of Texas Tech University, new information reinforces his claim that a much larger impact that he has named Shiva, actually did the dinosaurs in.

Dr Chatterjee has found a bigger crater—much bigger—in India. Estimated to be around 65 million years old, the massive sea floor structure was created at about the same time as a number of other impact craters and the Cretaceous-Tertiary (KT) extinction event. Although the site has shifted since its formation because of sea floor spreading, the formation is approximately 600 kilometers long by 400 km wide. It is estimated that a crater of that size would have been made by an asteroid or comet approximately 40 km (25 mile) in diameter. The explosion that caused it may have been 100 times the size of the one that created Chicxulub.

The Shiva crater is located beneath the Indian Ocean, west of Mumbai, India. It was named by paleontologist Chatterjee after Shiva, the Hindu god of destruction and renewal. At the time of the KT extinction, India was located over the Réunion hotspot of the Indian Ocean. Hot material rising from the mantle flooded portions of India with a vast amount of lava, creating a plateau known as the Deccan Traps. It has been hypothesized that either the crater or the Deccan Traps associated with the area are the reason for the high level of oil and natural gas reserves in the region.

Three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter) at the Mumbai Offshore Basin, western shelf of India from different cross-sectional and geophysical data. The overlying 4.3-mile-tick Cenozoic strata and water column were removed to show the morphology of the crater. Credit: S. Chatterjee.

Chatterjee presented his latest findings on Shiva to the annual meeting of the Geological Society of America in Portland, Oregon, on October 18th. He has identified an underwater mountain called Bombay High, off the coast of Mumbai, which measures 3 miles (5 k) tall from the ocean floor (about the height of Mount McKinley) from sea bed to peak and is surrounded by Shiva’s crater rim. Dr Chatterjee’s analysis shows that it formed from a sudden upwelling of magma that destroyed the Earth’s crust in the area and pushed the mountain rapidly upward. He argues that no force other than the rebound from an impact could have produced this kind of vertical uplift. Here are further arguments from a previous paper:

The KT boundary sections in India, though mostly destroyed by the Deccan lavas, have yielded an iridium anomaly, iridium-rich alkaline melt rocks, shocked quartz, nickel-rich spinels, nickel-rich vesicular glass, sanidine spherules, fullerenes, glass-altered smectites, and tsunami deposits. The last dinosaurs occur immediately below the iridium anomaly layer. The synchroneity of the Deccan Traps with the KT boundary, their geographic proximity with the crater, and the occurrence of a thick shocked quartz layer below the lowermost lava flow strongly imply that the Deccan volcanism may have been triggered by the Shiva impact. The impact was so intense that it led to several geodynamic anomalies: it sheared and deformed the lithospheric mantle across the western Indian margin and contributed to major plate reorganization in the northwestern Indian Ocean. This resulted in a 500-km displacement of the Carlsberg Ridge and initiated rifting between India and Seychelles. The oblique impact may have generated spreading asymmetry, possibly linked to the sudden northward acceleration of the Indian plate in Early Tertiary.

During the late Cretaceous, India was an island continent much like Australia is today. The sub-continent did not take up its familiar position in the south of Asia until 50m years ago, when it collided with that continent. The late Cretaceous was also a period of great volcanic activity, a time when huge eruptions created fields of basalt as much as two kilometers thinck. Before the discovery of the Chicxulub crater, these eruptions had been put forward as an explanation for the death of the dinosaurs—altering the climate and hastening their extinction. Even after Walter Alvarez's discovery of iridium deposits around the world and the identification of the Chicxulub crater in the Yucatan, some argued that the eruptions were a major contributing cause to the extinction.

The world around the time of the KT boundry. Credit: C Scotese.

Further examination of the crater revealed rich deposits of shocked quartz and iridium, minerals that are commonly found at impact sites. More importantly, the rocks above and below Shiva date it to 65m years ago, the time of the KT extinction . Dr Chatterjee therefore suggests that an object 40km in diameter hit the Earth off the coast of India and forced vast quantities of lava out of the Deccan Traps. As well as killing the dinosaurs the impact caused the Seychelle Islands to break away from India. These islands and their surrounding seabed have long looked anomalous to geologists, being made of continental rather than oceanic rock. The seem more like a small part of a continental land mass rather than genuine oceanic islands.

Some say that the Shiva complex adds weight to the theory that the KT extinction was caused by a massive asteroid fragmenting and hitting the Earth in several locations, known as the “multiple impact theory.” Extensive dating research at Chicxulub has suggests that the impact occurred 300,000 years earlier than the dinosaur extinction, meaning there really should be two ejecta layers. That no one had noticed two distinct layers previously could be explained by the fact that the accumulation of sediment in most rocks is so slow that the two layers merged together. After all, 300,000 years is a blink of an eye in geologic terms. Alternatively, it could be that no one has been looking for two layers, so they have not noticed the double signature or have ignored its significance. Indeed, two iridium layers have been found in some places. One such site is at Anjar, an Indian town north of the impact site.

This painting depicts an asteroid slamming into tropical, shallow seas. The aftermath of this immense asteroid collision, which occurred approximately 65 million years ago, is believed to have caused the extinction of the dinosaurs and many other species on Earth. Painting by Donald E. Davis, NASA.

This is an excellent example of how science is continually updated and refined. This new information does not make Walter Alvarez wrong or a bad scientist, any more than Einstein's theories proved that Newton was wrong. It merely shows that there was even more to the cataclysmic events that transpired 65 million years ago than first suspected. As always, science did not rest but continued to seek more evidence which lead to new conclusions. It also underscores what a dangerous place the solar system we live in actually is (see “Forget Global Warming, The Sky Really Could Fall”). It now seems that the Chicxulub strike, as bad as it was, was only a warning shot. The dinosaurs, the dominant lifeforms on the planet at the time, didn't take the hint and evolve sufficiently to create a space program capable of deflecting subsequent asteroids: sic transit gloria mundi.

The picture that has emerged requires a set of coincidences, but as I have noted before in this blog, given a half a billion years or so and any set of coincidences can happen, perhaps more than once. The true nature of the universe is revealed in the chain of events that transpired. The scenario goes like this: First, two of the biggest impacts in history happened within 300,000 years of each other; second, the impacts coincided with one of the largest periods of volcanic activity in the past billion years; and third, one of them just happened to hit where the volcanoes were most active. As The Economist put it, “what really killed the dinosaurs was a string of the most atrocious bad luck.”

Be safe, enjoy the interglacial and stay skeptical.

Beastly bad luck, old boy.