Scientists know that the Earth has witnessed five mass extinctions to date, and there is growing concern that we might be headed toward the sixth.
Now, new research regarding the most deadly mass extinction -- which occurred some 252 million years ago, at the end of the Permian period -- provides an unsettling picture of what can happen when the earth's atmosphere is inundated with greenhouse gases -- namely carbon and methane.
In this event, coined “the Great Dying,” over 90% of marine species and 70% of terrestrial vertebrate species went extinct. It took about 10 million years for life on Earth to recover from this catastrophic event.
Scientists have proposed a number of possible culprits responsible for this mass extinction, including an asteroid impact, mercury poisoning, a collapse of the ozone layer, and acid rain. Heavy volcanic activity in Siberia was suspected to play a key role in the end-Permian event.
But new research from Dr. Benjamin Burger of Utah State University’s Uintah Basin Regional Campus shows that the Great Dying might have transpired a bit differently than previously suspected.
During the Permian, Earth’s continents were still combined as one Pangea, and modern day Utah was on the supercontinent’s west coast. Samples from the end-Permian have been collected from rock layers in Asia, near the volcanic eruptions, but Utah was on the other side of Pangaea. Burger’s samples could thus provide a unique perspective of what was happening on the other side of the world from the eruptions.
Burger's data revealed a menacing situation brewing on Earth at the end of the Permian period:
A sharp drop in calcium carbonate levels indicated that the oceans had become acidic. A similar decline in organic content matched up with the immense loss of life in the oceans during this period. The presence of pyrite pointed to an anoxic ocean (without oxygen), meaning the oceans were effectively one massive dead zone.
Bacteria ate the oversupply of dead bodies, producing hydrogen sulfide gas, creating a toxic atmosphere. The hydrogen sulfide oxidized in the atmosphere to form sulfur dioxide, creating acid rain, which killed much of the plant life on Earth. Elevated barium levels in the samples had likely been carried up from the ocean depths by a massive release of methane.
And the cause of the Earth's turmoil at this time? Burger believes it very well might have been coal deposits, formed during the Carboniferous period and ignited by underground magma resulting from the Siberian volcanic eruptions 300,000 years earlier.
The coal ignition triggered the series of events that led to Earth’s worst mass extinction. Its sulfur emissions created the acid rain that killed forests. Its carbon emissions acidified the oceans and warmed the planet, killing most marine life. The dead bodies fed bacteria that produced toxic hydrogen sulfide gas, which in turn killed off more species. The warming of the oceans produced a large methane release, which accelerated global warming faster yet.
It is difficult not to draw comparisons between Burger's portrayal of events preceding the Great Dying and environmental concerns today -- from warming oceans and growing dead zones to the potential for massive doses of methane released from thawing permafrost.
There are an increasing number of dead zones in the oceans. Burning coal was causing acid rain, although we largely solved that problem through Clean Air Acts, and in the US, a sulfur dioxide cap and trade system implemented by a Republican administration.
We’ve had less success in tackling carbon dioxide pollution, which continues to rise. As a result, the oceans are becoming increasingly acidic, and temperatures increasingly hot. Scientists today also worry about potentially large releases of methane from the ocean floor and Arctic.
"[T]here are clear indications that losing species now in the ‘critically endangered’ category would propel the world to a state of mass extinction that has previously been seen only five times in about 540 million years. Additional losses of species in the ‘endangered’ and ‘vulnerable’ categories could accomplish the sixth mass extinction in just a few centuries. It may be of particular concern that this extinction trajectory would play out under conditions that resemble the ‘perfect storm’ that coincided with past mass extinctions: multiple, atypical high-intensity ecological stressors, including rapid, unusual climate change and highly elevated atmospheric CO2."