The Earth giveth and the Earth taketh away

We all know the story of the great big asteroid impact that brought about the demise of the dinosaurs (and this geological event is so popularly known that I'm sure it will feature as the subject of a future postcard). However, the dinosaur-ending mass extinction pales in comparison to one particular event that occurred about 250 million years ago.

This event marks the boundary between the Permian and Triassic geologic periods. The Permian was a time when the Earth contained a single supercontinent—Pangaea—vast areas of which were covered by arid deserts. But in a relatively abrupt period a large proportion of life on Earth was lost. In all, over 90% of marine species and 70% of terrestrial vertebrates became extinct.

The Pangaea supercontinent existed during the Permian and Triassic periods.
Credit: Mikkel Juul Jensen / Bonnier Publications / SPL

Until recently, however, the cause of this 'Great Dying' has remained unclear. But new work, presented at the American Geophysical Union's December 2013 Fall Meeting in San Francisco, provides us with a smoking gun.

Accurate measurements, conducted by geologists Seth Burgess and Samuel Browning at MIT, on rocks from Meishan in the Zhejiang Province of China give a new and precise age for the actual Permian–Triassic boundary that marks this extinction. They show that the extinction began 251.941 million years ago and lasted until 251.880 million years ago, i.e., lasting for 61,000 years.

That time frame shortly follows the first eruptions of vast volcanic flows in Siberia 252.28 million years ago. These Siberian Traps cover an area of about 2 million km² (about the size of western Europe) and represent one of the largest eruptive events in Earth's history.

Part of the vast Siberian Traps. Credit: Jon Ranson

For decades scientists have questioned whether these two great, and closely spaced, markers in Earth's life could be linked and if the volcanic eruptions may have somehow caused the extinction. With the new age dating it is possible to at least show that the volcanism temporally preceded the mass extinction.  It is up to other scientists to work out what mechanism(s) link the two and could have caused so much destruction.

One recently proposed scenario sees huge amounts of sulfur dioxide from the volcanic eruptions being injected into the atmosphere. Acid rain, with the pH of lemon juice, would have then rained down on the northern hemisphere to wreak havoc on its vegetation and for the animals reliant upon it. Other materials, originating from the coal deposits through which the Siberian Traps were erupted, are likely to have been forced into the atmosphere. A resulting toxic metal-bearing layer of ash is thought to have blanketed the northern hemisphere and played a large part in the extinction event.

Although our Earth provides us with the conditions and materials to sustain life, it can also turn on its geological nastiness from time to time and try its hardest to kill us. I'd send some of these informative rocks from southern China and Siberia into space for one of our alien planetary geologists to find. So they know just how Mother Earth likes to do her 'loving'.