'Hercynian' Mountain Range: How Earth Evaded Global Warming Last Time Around

Humanity's current climate dilemma is not the first time Earth has had to battle global warming. Around 300 million years ago, Earth evaded the same problem despite a huge spike in carbon dioxide levels, and geologists are just figuring out how it was done.

As it turns out, the "Hercynian" mountains that formed in the middle of the ancient supercontinent, Pangea, were the key.

Pangea was created as a result of moving plate tectonics. Much of the land surface was far from the sea, and so the continent became increasingly arid due to lack of humidity - which in turn reduced rock weathering.

Normally, when rock weathering drops carbon dioxide (CO2) levels rise, and yet, CO2 levels continued to drop, as they had been prior to the mountain formation. During that time, CO2 levels were reduced to the lowest of the last 500 million years.

According to team leader Dr. Yves Godderis, these mountains - running from what is now the Appalachians, through to Ireland, South-Western England, Paris and the Alps into Germany, and on further East - promoted rock erosion, and so atmospheric CO2 was able to continue its descent.

"If it hadn't been for the formation of the Hercynian mountains, the atmospheric CO2 levels would have reached around 25 times the pre-industrial level, meaning that CO2 levels would have reached around 7,000 parts per million (ppm)," Godderis explained.

Compare that to present day, which boasts CO2 levels around 400 ppm. If we were to experience a rise in greenhouse gases equivalent to what could have happened millions of years ago, that means we would see CO2 rise to a level around 17 times what they are currently.

And even if these mountains never formed and didn't save the day, researchers believe CO2 levels would still have eventually fallen.

Increasing temperatures would have promoted rock weathering - heat compensating for the scarcity of water - which in turn would have removed CO2 from the atmosphere, thus stopping the rising temperatures.

"So it would eventually have been self-correcting," Godderis said.

Though, he adds, it would mean that we would be looking at a very different Earth today if high temperatures had persisted.

This work is being presented to the Goldschmidt geochemistry conference in Sacramento, California.