Monday, 21 November 2011

A Devastating Double Death For The Dinosaurs

In March, 2010, a panel of scientists concluded that the widely acclaimed Chixulub meteorite strike, 65 million years ago, was the primary cause of the extinction of the dinosaurs. Yet it is thought that there were many secondary factors and events which contributed to this sudden destructive event. One of the most popular was that massive, global volcanic events caused huge climatic shifts over such a short space of time, that the dinosaurs were unable to adapt and so died out, leaving behind nothing but bones and their avian descendants.

Yet a team of scientists, led by Dr Gerta Keller from the Department of Geoscience at Princeton University, believe that they have found substantial evidence to suggest that the Cretaceous Earth did indeed suffer a double death from the meteorite strike and volcanic events. Their research was centred around a massive marine eruption known as the Deccan Trap Basalt Floods. A basalt flood event occurs on a plate boundary. A sudden seismic shift allows a vast body of magma to flood out of the Earth's mantle.

The volume of magma is so great that the surrounding water does not cool the mass down to a solid state and so the hundreds of million of tones of molten material surge across the sea bed, destroying all in its path. The Deccan traps released so much magma, that an area covering 1.5 million square kilometres was entombed in rock. The event was actually composed of multiple eruptions over a period of 30,000 years. The team used plankton fossils embedded within the sediment and volcanic strata to gauge the magnitude of the events.

When they correlated the data with the proposed series of events, they came to the conclusion that the massive, prolonged eruptions caused a gradual elimination of species that lived during the K-T boundary. The largest miniature extinction event coincided with the elimination of nearly 100% of the planktonic species in the area. A sub-division within the team also found evidence of a small meteorite strike near to the Deccan traps which stuck close to the time period of the largest event.

The fossil plankton arranged to represent the decline in diversity during the Deccan Trap events
This impact event would have released a blast of energy 2 million times more powerful than the Hiroshima bomb. When Dr Keller looked at all of the evidence, she came to the conclusion that the Chixulub collision would not have been enough to destroy the dinosaurs as well as the thousands of other species which perished 65 million years ago. Yet the largest Deccan Trap event coupled with the small meteorite strike, and the Chixulub event, would have released enough energy to cause such an extinction.

'Our work in Meghalaya and the Deccan Traps provides the first one-to-one correlation between the mass extinction and Deccan volcanism,' said Keller. Keller is one of the prominent scientists who reject the importance of the Chixulub event in the K-T extinction event. Her basis for this theory is the way the dates do not align with the dates of the extinction. A sediment core taken from the impact crater in 2003 shows that the meteorite struck the Gulf of Mexico 300,000 years prior to the death of the Cretaceous dynasty. 

However the Deccan trap events lie far closer to the K-T boundary. There were three eruptions. One pre-dates the extinction by 2 million years and one occured 300,000 years after, roughly at the same time as the Chixulub event. However the middle event, Deccan phase-2, coincided exactly with the iridium rich layer which marks the K-T boundary and accounts for 80% of the total volcanism. This second event alone released 30 times the amount of sulphur and carbon dioxide than the Chixulub event.

This would have sent the Earth's climate into an erratic and highly volatile phase. The meteorite that stuck the Gulf of Mexico was simply the final nail in the coffin of the dinosaurs. 'Our data suggest that the mass extinction of the dinosaurs and other species was caused by the harsh conditions resulting from massive Deccan eruptions and the coincidence of multiple meteorites,' Keller said. 'In light of this new evidence, the single-impact story seems more like an article of faith at this point.'