Published on Jan 11, 2013
250 million years ago, long before dinosaurs roamed the Earth, the land and oceans teemed with life. This was the Permian, a golden era of biodiversity that was about to come to a crashing end. Within just a few thousand years, 95% of the lifeforms on the planet would be wiped out, in the biggest mass extinction Earth has ever known. What natural disaster could kill on such a massive scale? It is only in recent years that evidence has begun to emerge from rocks in Antarctica, Siberia and Greenland.
The demise of the dinosaurs, 65 million years ago (at the so-called K/T boundary), was as nothing compared to the Permian mass extinction. The K/T event killed off 60% of life on Earth; the Permian event 95%. Geological data to explain the destruction have been hard to find, simply because the rocks are so old and therefore subject to all kinds of erosion processes. It seems plausible that some kind of catastrophic environmental change must have made life untenable across vast swathes of the planet.
In the early 1990s, the hunt for evidence headed for a region of Siberia known as the Traps. Today it’s a sub-Arctic wilderness but 250 million years ago, over 200,000km² of it was a blazing torrent of lava. The Siberian Traps were experiencing a ‘flood basalt eruption’, the biggest volcanic effect on Earth. Instead of isolated volcanoes spewing out lava, the crust split and curtains of lava were released. And the Siberian flood eruption lasted for millions of years. Could volcanic activity over such a long time alter the climate enough to kill off 95% of life on Earth?
Vincent Courtillon used a much smaller flood basalt eruption, in Iceland in 1783, as the basis for some calculations. Writing in the 18th century, Benjamin Franklin (then American Ambassador in Paris) described 1784 as a year without a summer. Ash from the eruption blacked out the sky and crops failed across Europe. Courtillon extrapolated the climatic impact of the Siberian Trap eruption from the records of the Icelandic event. He deduced that a ‘nuclear winter’ lasting decades would be followed by rapid global warming due to the increased level of greenhouse gases in the post-eruption atmosphere.
Vincent believes the disruption of cooling followed by warming could cause the Permian extinction but other geologists disagree. Peter Ward returned to the Siberian Trap data to estimate the amount of carbon dioxide – and global warming – that could result. His worst case scenario is a temperature rise of 5°C, enough to kill off many species but not the 95% wipeout that ended the Permian.
If the Siberian eruptions were not deadly enough, what other effects might be at work? To try to answer that, Michael Rampino set out to establish an even more fundamental piece of data: how long did the extinction take? He studied rock sedimentation rates in the Alps and concluded that the Permian killer had stalked the planet for just 8,000-10,000 years, far less than had been thought. His mind turned to ways of causing such catastrophic destruction in – on geological timescales – the blink of an eye. He wanted to explore the possibility of a meteorite strike.