The same noxious compounds released from burning coal and crude oil may have devastated forests and the early dinosaurs that lived in them 200 million years ago.
Scientists have known for decades of a massive dying between the Triassic and Jurassic eras. Life around the world was pummeled by runaway global warming, and scientists speculate that huge volcanic eruptions are responsible, belching vast amounts of carbon dioxide (CO2) into the atmosphere.
But a new study suggests polycyclic aromatic hydrocarbons (PAHs) and sulphur dioxide (SO2), two highly toxic pollutants common in fossil fuels, were released in huge quantities and played a role in snuffing out the lush forests of the northern hemisphere along with many species of early dinosaurs.
Bas van de Schootbrugge of Goethe University Frankfurt in Germany and a team of researchers discovered the toxins in concentrations over 1,000 times normal levels in rock samples from Germany and Sweden. They coincide with an enormous convulsion of volcanic eruptions that stretched from Brazil to France that split the supercontinent Pangea in half. The fiery rift would one day become the Atlantic Ocean.
Enough lava poured from the eruptions to bury the contiguous United States under a layer of molten rock 300 meters (984 feet) deep. Much of it infiltrated coal seams and cooked them, with the same results as a modern-day coal-fired power plant: huge amounts of carbon dioxide (CO2), sulfur dioxide, and PAHs were vented into the atmosphere.
"PAHs are very toxic," van de Schootbrugge said. "In places where people burn coal to heat their homes today, the gases are a major health problem."
With CO2 streaming into the atmosphere, global warming was rampant. PAHs added to the misery by poisoning plants and soils. They could have stripped away the ozone layer, too, the team theorizes, if they made it up into the stratosphere.
Sulfur dioxide may have provided the final nail in the coffin, mixing with water and falling on land as potent acid rain.
The study was published Sunday in the journal Nature Geoscience.
However, Gregory Retallack of the University of Oregon argued that there wasn't enough sulfur to damage plant life on land. He thinks carbon dioxide was primarily to blame, choking off oxygen in the abundant ancient swamplands and suffocating trees' root systems. PAHs could've exacerbated stress on plants and animals, but probably didn't drive the extinction.
"It's a very interesting idea, it's a just question of dosages," he said. "We're not sure what the dose of PAHs would've been. It's a fine line between petrol sniffing and petrol poisoning."