12 December 2013
Long before the dinosaurs died off, the “Great Dying” killed nearly all life in the ocean, 70 percent of terrestrial animals and even insects. But this mass extinction more than 250 million years ago – Earth’s greatest natural disaster – is still a scientific mystery. Little evidence remains of why and when life on the planet crashed to this long pause.
The event is, however, etched in stone. A thin layer of rock reveals it occurred at the end of the Permian period, before the Triassic. Several years of research suggest the trigger may have been volcanic. Massive eruptions in present-day Siberia occurred during the same period. They released enough magma to cover the United Sates in a mile-deep lava layer.
The deadly deluge might have triggered the apocalypse at the end of the Permian, but scientists are not sure the eruptions came before the extinction. Recent research using EARTHTIME, an improved technique for radioisotope analysis, suggests the outpouring of magma preceded the deadly standstill.
Researchers from the Massachusetts Institute of Technology re-analyzed uranium and lead isotope ratios in zircon crystals from south China, and found striking differences in the age of these previously studied samples.
“We attribute the difference in dates on the same rock from two different studies, in part, to different tracer composition,” said Seth Burgess, a geochronologist at MIT who presented the new work Wednesday morning at the American Geophysical Union’s Fall Meeting in San Francisco.
New samples from the Siberian magma deposits also suggest the geologic ruckus started 340,000 years earlier than previously thought. It also ended quickly. Rather than extending over a period of 100,000 years, the extinction event probably ended within approximately 60,000 years. The samples also reveal hundreds of meters of volcanic rocks and lava erupted just before the start of the extinction.
“Nobody really knows where all that magma came from, and how such a massive amount of magma was generated in the crust at that time,” Burgess said.
For now, the new dates firmly place volcanic activity before the massive die-off. Having a more precise timeline allows researchers to correlate biological and climate data with geological records to understand the end-Permian extinction.
“For the first time ever, we can say the relative timing of these two events permits a causal connection between the two – not that it definitely caused the extinction,” Burgess said.
The extreme volcanic activity might have set off cataclysmic environmental changes across the globe, according to a model of prehistoric climate presented by Benjamin Black, geology researcher at MIT.
The models predicted vast swaths of land that received years of acid rain as strong as undiluted lemon juice. Within weeks of such showers green leaves turned to blistered blobs, biologists have shown. Over the course of a year, the sulfurous rain might have stunted prehistoric vegetation across large parts of the planet. The chemical cocktail that caused acid rains may have also punched a giant hole in the ozone layer, adding higher UV radiation to the uncomfortable end of the Permian.
“Potentially in conjunction with other kinds of environmental stresses, these kind of atmospheric changes can provide a direct link between Siberian volcanism and biological effects,” Black said.
– Jyoti Madhusoodanan is a science communication graduate student at UC Santa Cruz