Long before an asteroid ended their domination of the planet, dinosaurs survived a different worldwide event – a bout of global warming that ended the Triassic era. In new research, scientists have estimated the volcanic carbon dioxide that made this happen, finding the era was punctuated by bursts of CO2 emissions similar to those being released by humans today, although over longer periods of time.
Most of the Earth's great extinctions appear to coincide with eruptions of vast volcanic provinces, altering the atmosphere and oceans. In an attempt to understand these catastrophes, Dr Manfredo Capriolo of the University of Padova, Italy, studied basaltic rocks from what is known as the end-Triassic Central Atlantic Magmatic Province (CAMP).
Today, the province is split between three continents, with the largest share beneath the Amazon and secondary areas in North America and Africa. Two hundred million years ago, however, these landmasses lay next to each other and the end-Triassic CAMP was one united region, into which vast quantities of material from the mantle flowed.
The basaltic rocks the team studied are rich in bubbles that indicate the presence of carbon dioxide released during the eruptions. By studying the size of these bubbles, they were able to estimate the amount of gas that accompanied the eruption of each tonne of magma. When they multipled across the estimated size of the deposited rocks, the total quantity of CO2 released dwarfed the amounts produced by the burning of fossil fuels and felling of rainforests today. However, the eruptions occurred over hundreds of thousands or millions of years so annual emissions were much lower.
On the other hand, rather than a single period of continuous eruption, Capriolo and co-authors argue in Nature Communications that the CAMP was formed from a series of pulses lasting around 500 years. A typical pulse might involve 10,000 cubic kilometers of magma and would have released about as much carbon dioxide as humans are currently on target to emit during the course of the 21st Century.
As a consequence, Capriolo concludes, the end-Triassic involved a series of rounds of greenhouse gas emissions, each similar in size to what we are experiencing today, but probably spread over several centuries rather than just one. These would have heated the planet and made the oceans more acidic, followed by an interlude where CO2 levels fell, before the next pulse occurred.
The combined effect was to drive more than half the species on the planet to extinction. Dinosaurs, which had previously faced substantial competition for ecological niches, came to dominate the land, despite the loss of many individual species.
The consequences of packing such an event into a single century are likely to be even more disruptive.