Huge volcanic eruptions 233 million years ago pumped carbon dioxide, methane and water vapor into the atmosphere. This series of violent explosions, on what we now know as Canada’s west coast, led to massive global warming. Our new research has revealed that this was a planet-changing mass extinction event that killed many of the dominant tetrapods and heralded the dinosaurs’ dawn.
The best known mass extinction occurred at the end of the Cretaceous 66 million years ago. This is when dinosaurs, pterosaurs, marine reptiles and ammonites all died out. This event was primarily caused by the action of a giant asteroid that darkened the sun̵
Geologists and paleontologists agree on a list of five such events, of which the last Cretaceous mass extinction was the last. So our new discovery of a previously unknown mass extinction may seem unexpected. And yet, this event, called the Carnian Pluvial Episode (CPE), seems to have killed as many species as the giant asteroid did. Ecosystems on land and at sea were greatly altered as the planet became warmer and drier.
On land, this triggered profound changes in plants and herbivores. In return, the dinosaurs got their chance with the decline of the dominant herbivorous tetrapods, such as rhynchosaurs and dicynodonts.
The dinosaurs originated about 15 million years earlier, and our new study shows that as a result of CPE, they expanded rapidly in the subsequent 10 million to 15 million years and became the dominant species in the terrestrial ecosystems. CPE triggered the “age of the dinosaurs”, which lasted for another 165 million years.
It was not only the dinosaurs that gained a foothold. Many modern tetrapod groups, such as turtles, lizards, crocodiles and mammals, date back to this newly discovered time of revolution.
To follow the tracks
This event was first noticed independently back in the 1980s. But it was thought to be limited to Europe. First, geologists in Germany, Switzerland, and Italy recognized a large turnover among marine fauna about 232 million years ago, called the Rheingraben event.
Read more: Five mass extinctions – and what we can learn from them about the planet today
So in 1986, I independently recognized this as a global turnover among tetrapods and ammonites. But at that time, the age date was much weaker than now, and it was impossible to be sure whether these two were the same event.
The plugs began to fall into place when an episode of about 1 million years of humid climate was recognized throughout Britain and parts of Europe by geologists Mike Simms and Alastair Ruffell. Then geologist Jacopo dal Corso discovered a coincidence in the timing of CPE with the peak of eruptions of the Wrangellia basalts.
Wrangellia is a term that geologists give to a narrow tectonic plate attached to the west coast of the North American continent, north of Vancouver and Seattle.
Finally, in a review of the evidence from stones of the Triassic age, the signature of the CPE was demonstrated – not only in Europe but also in South America, North America, Australia and Asia. This was far from being a single European event. It was global.
The massive Wrangellia eruptions pumped carbon dioxide, methane and water vapor into the atmosphere, leading to global warming and an increase in precipitation worldwide. There were as many as five impulses of eruptions associated with warming peaks from 233 million years ago. The eruptions led to acid rain as the volcanic gases mixed with rainwater to shower the soil in dilute acid. Shallow oceans were also acidified.
The sharp warming drove plants and animals from the tropics, and the acid rain killed plants on land, while the acidification of the sea attacked all marine organisms with carbonate skeletons. This removed the oceans and land surfaces. Life may have begun to recover, but when the eruption ceased, temperatures remained high while tropical rainfall ceased. This is the reason for the subsequent drying of the land where the dinosaurs flourished.
Most extraordinary was the recasting of the marine carbonate factory. This is the global mechanism by which calcium carbonate forms large thicknesses of limestone and provides material for organisms such as corals and mollusks to build their shells. CPE marked the beginning of modern coral reefs as well as many of the modern groups of plankton, suggesting profound changes in marine chemistry.
Before CPE, the main source of carbonate in the oceans came from microbial ecosystems, such as limestone-dominated mud heaps, on continental shelves. But after CPE, it was driven by coral reefs and plankton, where new groups of microorganisms, such as dinoflagellates, emerged and flourished. This profound shift in basic chemical cycles in the oceans marked the beginning of modern marine ecosystems.
And there will be important lessons for how we help our planet recover from climate change. Geologists need to study the details of the volcanic activity in Wrangellia and understand how these repeated eruptions drove the climate and changed the earth’s ecosystems. There have been a number of volcanic-induced mass extinctions in Earth’s history, and the physical disturbances, such as global warming, acid rain, and ocean acidification, are among the challenges we see today.
Paleontologists need to work more closely on the data from marine and continental fossil records. This will help us understand how the crisis played out in terms of the loss of biodiversity, but also to examine how the planet recovered.