The chances that asteroid impacts and huge bouts of volcanism coincide randomly to cause mass extinctions may be greater than previously imagined. UK researchers conducted statistical tests to determine the probability of such catastrophic events happening at the same time in Earth history. They found massive releases of lava and space collisions should have overlapped three times in the last 300 million years. Details will be published in a future issue of the geological journal Lithos. The work has been done by Dr Rosalind White and Professor Andy Saunders of the University of Leicester. The probabilities they calculated assumed there was no causal link between the two phenomena - that impacts from space did not set off the volcanism. Flood basalts, as the term suggests, are formed by massive outpourings of lava from beneath the Earth. Hundreds of thousands of cubic km of material can be spewed on to the surface in short geological timescales. These eruptions have, like space impacts, been blamed for some of Earth's mass extinctions due to the environmental changes they may trigger. The Leicester authors contend that because impacts and flood basalts occur more frequently than mass extinctions, it is unlikely the two phenomena bring about mass extinctions on their own. However, mass extinctions may be triggered when the two events occur together, they argue. There is evidence of both phenomena happening at the same time 65 million years ago, when the dinosaurs disappeared from the fossil record. The impact that created the 180km-wide impact crater at Chicxulub in Mexico is generally thought to have played a major part in this extinction.
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