Are we facing the sixth extinction?

  • September 10, 2013

Roelant Savery's The Paradise, showing a dodo in the lower right corner. Image courtesy of Wikipedia Commons

Five major extinctions have rocked life on Earth, one of which was characterised by unprecedented increases in temperature. Simply put, it became too hot to survive. With temperatures rising every year, are we headed for a similar fate?

“Humankind has a critical responsibility, now more than ever, to avoid a sixth mass extinction. We have the opportunity to change the impact we are having,” says Lindsay Marshall, marketing and communications manager at Maropeng.

During the five periods of mass extinction, huge numbers of species of life died out due to wide-scale environmental changes. Although the debate surrounding the extinction of dinosaurs will no doubt continue for many years to come, a hybrid theory, volcanism combined with an asteroid strike, seems to answer most questions surrounding the disappearance of the dinosaurs.

Using radiometric dating analysis of rock and ash samples, an international team of scientists has established that the dinosaurs died out around 66 038 000 years ago, a more accurate date than was previously believed.

This is according to the findings published in the February 8 issue of Science journal by a research team headed by Paul Renne, and comprising scientists from Berkeley Geochronology Center and the University of California at Berkeley in the US, Glasgow University in the UK, and Vrije Universiteit Amsterdam in the Netherlands.

The findings show a correlation between the latest extinction date with a theory that an asteroid that hit Mexico killed off all dinosaurs except birds.

“The hybrid theory, however, suggests that it was in fact a combination of climate change prompted by volcanic eruptions, and culminating in the asteroid strike, that led to the extinction,” explains Marshall.

There is evidence that animals that roamed the Earth at the time were stressed by several unseasonal cold snaps towards the end of the Cretaceous Period. The discovery of iridium in the 1980s by father-and-son team Luis and Walter Alvarez established that a layer of clay found throughout the world, which marks the end of the Cretaceous period, is iridium-enriched. Iridium is a common component of space rocks, which led to their theory that an asteroid impact had wiped out the dinosaurs.

The Chicxulub crater, formed by the impact of an estimated 10km-diameter asteroid, would have resulted in a sunlight-blocking dust cloud that wiped out plant life and reduced global temperature. The force of the Chicxulub impact would have been equal to the simultaneous explosion of two million hydrogen bombs. However, the asteroid impact may still not be the whole story in the end-Cretaceous extinction.

Volcanism, as well as climate change, could have played a powerful catalytic role. Volcanoes have caused dramatic changes in the world’s climate. The 1815 eruption of Mt Tambora in Indonesia, for example, blasted 100 cubic kilometres of rock into the atmosphere. The climatic effects of the eruption of Tambora were so extreme, the year Tambora erupted was often referred to as "the year with no summer" because those living in north-eastern United States experienced frost nearly every day.

However, scientists believe volcanism alone was not enough to cause extinction. It’s more likely that volcanism was a contributing factor to a change in the world’s environment.

“We also know that there were changes in sea level around the same time, possibly due to a decrease in global temperatures as a result of climate change or due to one of the cyclical events experienced by planet Earth,” Marshall says.

So while climate change appears to have played a part in the extinction of dinosaurs, it was not the only time climate played a role in mass extinction.

Going back to around 250-million years ago, before dinosaurs ruled the Earth, there was the end-Permian mass extinction, which was followed by tens of thousands of years without the appearance of new species.

Scientists now believe that this was because extremely high temperatures (around 50°C on land) severely reduced the chances of survival at the time.

If alarm bells are ringing, it’s because the rise in temperature over the past 100 years or so is exactly what environmentalists are concerned about.

In fact, many scientists claim that currently we are experiencing a sixth mass extinction, propelled by human industrial development. The lack of life following the end-Permian extinction was caused by a breakdown in a familiar cycle: plants converting carbon dioxide (CO2) into oxygen. After the extinction, there was significantly less plant life, and that meant more CO2, which in turn meant higher temperatures.

“We may be facing a similar scenario – not because of a lack of plant life, but because of the significant increase in CO2 levels as a result of a variety of human activities. The reality is that we need to be conscious of our activities and what the effects are on our planet, or the consequences could be devastating. Now is the time to act and start making a difference,” Marshall concludes.

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