A prominent mathematician has closely analysed the Earth’s five previous mass extinction events and found that a sixth is just around the corner.
Over the last 540 million years our planet has experienced five of these devastating ecological events and in almost every case they involved disruption to the cycling of carbon through the oceans and then the atmosphere.
Since the 19th century, the planet has seen carbon dioxide levels rise alarmingly. However because we don’t have a point of reference with which to base it on it’s very difficult to judge if we are in fact heading for the sixth of these natural disasters.
To help us understand whether what we’re going through is the build up to an extinction event, Daniel Rothman, professor of geophysics in the MIT Department of Earth, has analysed the previous five mass extinction events and found that in all five examples there are “thresholds of catastrophe” in the carbon cycle, that if exceeded will ultimately lead to a mass extinction event.
So what is a threshold of catastrophe? Well put simply it can be one of two scenarios. The first is that if slow changes in the carbon cycle still manage to outstrip a global ecosystem’s ability to adapt. The second is when carbon unbalances take place over a much shorter timescale, at which point adapting goes out of the window and it’s simply the scale of the unbalance that determines how likely we are to have an extinction event take place.
Using this reasoning, Rothman applied his theory to our current rise in carbon dioxide levels and found that if a certain amount of carbon dioxide was added to the oceans on top of its existing levels it would result in a sixth mass extinction event.
In case you’re wondering how much carbon dioxide Rothman actually worked it out. It’s around 310 gigatons. Now while that might sound like a staggering amount (it is), it’s actually a line that the Earth will cross within this century.
As Rothman points out, unlike most disaster movies come 2100, the world wouldn’t simply just end.
“This is not saying that disaster occurs the next day,” Rothman explains. “It’s saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would behave in a way that would be difficult to predict. In the geologic past, this type of behaviour is associated with mass extinction.”
In fact a sixth mass extinction could take as long as 10,000 years. The end result however would still be the same.
It’s not all bad news, humanity has been able to drastically reduce the amount of carbon it places into the atmosphere, instead Rothman sees this as more of a wake-up call.
“There should be ways of pulling back [emissions of carbon dioxide],” Rothman says. “But this work points out reasons why we need to be careful, and it gives more reasons for studying the past to inform the present.”
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Five Previous Mass Extinctions
Ordovician-Silurian mass extinction
This happened around 433 million years ago. Most of the Earth’s living creatures were found in the oceans and a vast number of them died out over two distinct dying periods that lasted hundreds of thousands of years.
Late Devonian mass extinction
This took place around 359 million years ago and saw almost 75% of all life on Earth die out. The process took several million years but it resulted in almost all coral life being destroyed.
Permian mass extinction
This took place around 250 million years ago and is by far and away the worst extinction event to have taken place on Earth. Almost 96% of all living things on Earth died out. Astonishingly everything that lives on our planet is descended from the tiny 4% that survived.
Triassic-Jurassic mass extinction
Climate change combined with volcanic activity are all to blame for this smaller but no less deadly event that took place around 200 million years ago. Roughly half of all species on Earth died out during this period however it’s interesting to note that most plant life actually survived.
Cretaceous-Tertiary mass extinction
The latest and perhaps most well-known extinction event this is the one that killed off the dinosaurs. Climate change and flood basalt eruptions had already critically damaged the Earth’s ecosystem at which point a vast asteroid hit the planet, an act that many believe was the final nail in the coffin.
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