The Biggest Extinction on Earth

Yet the late Permian era suffered a second affliction. Over thousands of years, greenhouse gases belched out by the traps accumulated in deadly quantities. Carbon dioxide, water vapor and methane shrouded the earth, trapping heat. It is estimated that levels of carbon dioxide were up to six times higher than today. All this translates to a 10ºC temperature rise in the Karoo basin.

Its effect can be read in the Karoo rock strata. Above the blues, grays and greens of the floodplain mud sits a layer of fiery red rock. This represents the moment that iron minerals in the mud and soil oxidized as they became exposed to the air. It marks the time that the lush oasis became the parched, dead land that we see today.

Effects in the oceans

Examples of some fossils from the Permian era.

The oceans also suffered. Geologist Paul Wignall from the University of Leeds in the UK examined the marine fossil record in Iceland from the Permian era. He found that the number of fossils gradually diminished, until there were none at all. At this point, Wignall analysed the rock and found that it contained many pyrite crystals. He points out that pyrite, also known as fools’ gold, cannot form in the presence of oxygen.

If pyrite was forming in the ocean, there couldn’t have been much oxygen. Normally, the deep ocean gets its oxygen from the poles: cold water absorbs oxygen from the atmosphere. This cold, dense, oxygenated water then sinks and moves along the sea floor towards the equator.

Two hundred and fifty million years ago, the oceans, like the land, heated up. Wignall has calculated that around the equator, temperatures would have approached 38 C, about the temperature of bath water. Near the poles, temperatures were more akin to what we experience in California today.

With no cold water at the poles, the oceans’ circulation system shut down. Life in the oceans began to die. Without oxygen, organic debris can’t decompose properly, and the bacteria that breaks down this dead matter produces toxic hydrogen sulphide. Today, this deadly, rotten-egg smelling gas is found in low oxygen environments like bogs and swamps. Back then, it devastated the oceans, making them stinking and poisonous.

These putrid oceans released vast amounts of hydrogen sulphide into the atmosphere, marking the final death toll for the few remaining species on land already battling drought and famine. A measly 5% of species escaped obliteration.

It took around 6 million years for biodiversity to return to normal. Today, it’s been 65 million years since the last major extinction event. Life is thriving, and it’s easy for us to forget that the world around us has been fundamentally shaped by colossal natural disasters. Our existence is more fragile than we imagine. Huge flood basalts, asteroid impacts, gamma ray bursts… they do happen. And they will happen again.

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National Geographic Magazine - When Life Nearly Came to an End - The Permian Extinction
http://www.nationalgeographic.com/ngm/0009/feature4/

BBC - The Day theh Earth Nearly Died
http://www.bbc.co.uk/science/horizon/2002/dayearthdied.shtml