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Burning coal was likely the key component of the world’s worst extinction event

As dramatic as a good asteroid strike can be, giant falling space rocks aren’t the only thing that has wiped out life on Earth. The mass extinction that ended the Age of Dinosaurs was actually the fifth time nearly everything died. Before the first dinosaur was ever born, an extinction event known as “The Great Dying” took place, a horrific series of events that choked, poisoned or burned multitudes of animals on both the land and in the seas. 70 percent of terrestrial vertebrates and 90 percent of sea life went extinct during this time 252 million years ago, with the devastation taking at least 10 million years to show signs of recovery. While many of the terrible details about how things died have previously been discovered, research out of Utah is helping piece together what started all this destruction in the first place.

Indirect effects of eruptions

With no sign of an asteroid strike in sight, researchers have been looking for other events that might have knocked the world’s climate and atmosphere so far out of balance that it became toxic for most creatures to breathe. There’s evidence that massive volcanic eruptions took place in Asia around the end of the Permian period, but they predated the fossil records of the Great Dying by 300,000 years. Furthermore, analysis of rock layers from Utah don’t show signs of direct volcanic impact at that time— instead of the metals like nickel that you’d expect to  be carried from underground by a volcano’s magma, deposits from the end of the Permian have extra mercury, lead and carbon-12, all of which are associated with burning coal.

The picture that then emerged was one where volcanic eruptions were a trigger for The Great Dying, but not the exact cause, as their ash wasn’t influential enough to reach around the world, such as to what is now Utah. Instead, the erupting lava seems to have hit and ignited massive coal beds that were originally deposited in Asia in the Carboniferous period. As that coal burned, it spread around the world, setting off the bigger chain of events that led to mass extinctions.

From coal to corrosion

The fallout from the burning coal might be enough to make a prehistoric therapsid dream of asteroid strikes. The soot from the coal led to severe changes in the planet’s climates, raising temperatures, and acidity, of the oceans. As the oceans warmed, barium levels indicate that more methane was released from the sea floor, trapping even more heat in the atmosphere. After all this, an abundance of pyrite that was formed at this time suggests that the oceans became depleted of oxygen, naturally leading to more dead marine animals. Those deaths were so abundant that the bacteria that set to work consuming corpses released an immense amount of hydrogen sulfide gas (H2S), bringing us to what happened to the poor creatures living on land.

Hydrogen sulfide gas is toxic in large doses, but more importantly can react with moisture in the air to form acidic sulfur dioxide (SO2). So as bacteria tried to clean up the oceans, their waste led to acid rain that started killing plant life on land. Between the toxic, burning atmosphere and a lack of plants, the food chain understandably would have collapsed, taking both herbivores and the carnivores that ate them with it.

Current costs of burning coal

The scariest part of all this is probably just how mundane the idea of burning coal seems today. Thanks to industrialization, we don’t even need the help of a volcano to burn massive amounts of the stuff around the world. Thankfully, air quality legislation has managed to take steps to reign in acid rain, so we’re not corroding our forests into pulp right now. However, the seas do seem to be starting to relive some of the Great Dying, as temperatures and pH levels have been rising in various patches of the ocean. Thankfully, unlike a volcano or asteroid strike, there’s more we can actually do to head off The Great Dying II, because that’s definitely a sequel nobody wants to ever see.

Source: Burning coal may have caused Earth’s worst mass extinction by Dana Nuccitelli, The Guardian

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