World's First Global Warming Was Caused by Earth's Earliest Animals

A new study has revealed that it was the introduction and evolution of the planet's first inhabitants that led to its first catastrophic mass extinctions.

A new study published in Nature Communications from researchers at the Universities of Exeter, Leeds and Antwerp, and the Vrije Universiteit Brussel has revealed that it was animals that were responsible for the Earth's first global warming.

The cause was the evolution of the planet's first creatures in the ocean that resulted in a break down of organic material on the seafloor introducing more carbon dioxide into the atmosphere. 

Bioturbation to blame for global warming

“Like worms in a garden, tiny creatures on the seabed disturb, mix and recycle dead organic material – a process known as bioturbation,” said Professor Tim Lenton from the University of Exeter in a statement. “Because the effect of animals burrowing is so big, you would expect to see big changes in the environment when the whole ocean floor changes from an undisturbed state to a bioturbated state.”

The scientists spotted a decrease in oceanic oxygen levels, associated with an increase in carbon dioxide, around 520 million years ago, the time when earthly animals first evolved. However, rock evidence collected indicated that sediment from that era was minimally disturbed.

This confused the researchers because it would indicate that these animals were not active enough to lead to such disastrous consequences. "The critical factor was to realize that the biggest changes happen at the lowest levels of animal activity," explained lead author of the study Dr Sebastiaan van de Velde, of the Vrije Universiteit Brussel.

The researchers were then able to deduce that the first bioturbators had an unusually massive impact, a realization they called the “missing piece of the puzzle.” From there, they designed a new mathematical model of Earth from that time.

“When we ran our model, we were surprised by what we saw. The evolution of these small animals did indeed decrease the oxygen in the ocean and atmosphere, but also increased atmospheric carbon dioxide levels to such an extent that it caused a global warming event," said Dr Benjamin Mills, from the University of Leeds.

Will history repeat itself

This was confirmation that the warming previously recorded by scientists was indeed caused by early animal life during the first 100 million years of its evolution. The catastrophic consequences saw the unfolding of several mass extinction events.

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“There is an interesting parallel between the earliest animals changing their world in a way that was bad for them, and what we human animals are doing to the planet now,” said Lenton. “We are creating a hotter world with expanding ocean anoxia (oxygen deficiency) which is bad for us and a lot of other creatures we share the planet with.”

The Intergovernmental Panel on Climate Change’s (IPCC) revealed in its fifth assessment report that human activities are responsible for 100% of the warming observed since 1950. Meanwhile, the United States' fourth national climate assessment similarly concluded that 93% to 123% of the warming observed from 1951 to 2010 was also human-led.