The Big Extinction

20 December 2001


The fall to earth of a asteroid some 65 million years ago was the death knell for the dinosaurs. The ash and debris from the collision and subsequent forest fires changed the earths climate causing a collapse of the food chain. The dinosaurs, at the top of that chain, were destined only to live in our imagination through the fossil cases of museums.

As dramatic as this was, it has not been the only catastrophe for life on our planet. In fact at least eight other world-wide mass extinctions have taken place and current evidence points to the majority of these being caused by climate change.

The most dramatic extinction event took place some 251 million years ago at the end of the period of time geoscientists call the Permian. This was the true big extinction as over 95% of all species dies out.

But what could case such as dramatic event? Many theories have been put forward, including massive volcanic eruptions and the impact of a comet. However, the latest theory getting a great deal of recognition involves the release of naturally occurring methane, a bad greenhouse gas, from beneath the ocean floor.

In some places on earth methane gas is produced as the result of the decay of dead plants and animals. When the conditions are right, such as in sediments on the sea floor, this methane can combine with water and, under the weight of the water and sediment above, freeze to produce substances known as gas hydrate.

Gas hydrate is a crystalline solid consisting of gas molecules, normally methane, each surrounded by a cage of water molecules. It looks very much like water ice. Gas hydrate is stable in ocean floor sediments at water depths greater than 300 meters. Recent surveys undertaken by Geoscience Australia with the French government have found what appears to be massive gas hydrate deposits on the Lord Howe Rise between Australian and New Caledonia.

Some geoscientists now believed that in the Permian sea levels dropped so that the gas hydrates were no longer stable and massive amounts of methane was released into the atmosphere. This increased in methane caused a super greenhouse situation in the atmosphere causing the land to heat up killing plant and animal life and the ocean currents to stagnate killing almost all marine life. This was a catastrophic event!

Scientists at Geoscience Australia have been undertaking research into the fossil evidence, and in particular those microscopic fossils from the period, at the time of this extinction to better understand what might have happened. In particular, the so called 'fungal spike' - the world wide growth of fungus on all the dead and decaying material during the extinction - is being investigated, and it may not be what it appears.

Surely all the talk of human caused greenhouse and climate change needs to be taken into perceptive when living things on earth have already been through these horrific super greenhouse events. It does tell us one thing, while we human might not survive in the long term, life and our planet surely will.

Topic contact: media@ga.gov.au Last updated: October 4, 2013