Around 56 million years ago, there was an unmistakably warm period that appeared out of nowhere. The climate changed rapidly over just 500,000 years, a geological blink of an eye; all across the planet, temperatures shot up by as much as 8°C (14.4°F), triggering regional extinctions and overthrowing entire ecosystems’ hierarchies.
Even though the climate change signal has been clear for some time, it wasn’t clear at all what actually triggered it. Now, according to a new Nature study, we’ve finally found the culprit: a volcanic supereruption, of sorts.
An international team of researchers led by the University of Southampton decided to take another look at the so-called Palaeocene-Eocene Thermal Maximum (PETM). They were well aware that a huge release of carbon dioxide took place at the time, but where did it come from?
Carbon sources leave a signature. For example, carbon-12 is the primary variant (isotope) of that element that is trapped within the fossil fuels that we burn. Tracing this isotope is one of the primary fingerprints indicating that we are the reason there is now so much carbon dioxide in the atmosphere.
The team in this case decided to analyze the geochemistry of the remnants of tiny sea creatures known as foraminifera. Their shells are normally made of calcium carbonate, and the carbon within them can be used by researchers to see what kind of chemistry – and carbon releases – featured in the seas of the world 56 million years before now.
Combining their data with a cutting-edge climate model, the team calculated not only how much carbon was unleashed during the PETM, but where it came from. The final tally was 30 times the amount released by all the fossil fuels humanity has combusted to date – and only one event happening at the time could explain such a vast quantity.
Back then, Greenland was splitting away from Europe, and the North Atlantic Ocean was taking shape. When this type of continental rifting occurs, large upwellings of mantle material take place at the central rifting zone. This triggers a high degree of melt, which generates profound volcanism.
The PETM, then, was almost certainly caused by this gigantic melting zone, permitting a long-lasting volcanic supereruption to change the face of the Earth, for better or worse.