Evolution of Earth's First Animals 500 Million Years Ago Caused Global Warming

Around 540 to 520 million years ago, what many scientists consider to be the first true animals began to emerge in Earth's oceans. This took place during a rapid increase in biodiversity referred to as the Cambrian Explosion.

Among those to evolve were tiny burrowing lifeforms that broke down and recycled organic material on the seafloor, a process called bioturbation.

The effect of these burrowing animals was so big that it actually altered the biogeochemistry of the oceans and atmosphere, leading to global warming that prevailed for the next 100 million years. That's according to a study published in the journal Nature Communications.

Biogeochemistry is the scientific discipline involving the study of the chemical, physical, geological and biological processes that govern the natural environment.

For the study, an international team of researchers led by Sebastiaan van de Velde from Vrije Universiteit, Brussels, constructed a mathematical model of Earth's early biogeochemistry in order to examine the changes that could have been caused by the planet's early animals.

"The presence and activity of animals in the seafloor (much like worms in garden soils) stimulates the breakdown of organic matter in the sediment," van de Velde told Newsweek. "When animals evolved, and the seafloor changed from an undisturbed one to a mixed seafloor filled with burrows, a lot of the organic matter stored there was broken down, leading to the consumption of oxygen and production of carbon dioxide (much like the burning of fossil fuels)."

"As this occurred on a global scale, oxygen was drawn down in the atmosphere, and carbon dioxide increased, leading to global warming", he said.

Scientists already knew that warming had occurred at this point in Earth's history, but did not think that it could be driven by animals.

According to the researchers, this warming may have created unfavorable conditions for the early animals and led to a series of mass extinctions. These events could teach us important lessons about humanity's current predicament, in which the world is warming and oxygen deficiency in the oceans is increasing, the researchers said.

"This study helps us to understand how life and the earth system are intimately linked, and shows interesting parallels with the climate change occurring today," van de Velde said.

Prior to the Cambrian Explosion, a wonderful variety of complex lifeforms had already evolved in a period known as the Ediacaran. But determining where these organisms fit on the tree of life has proven challenging. Some scientists have expressed doubt as to whether they can be classed as animals.

Ediacaran organisms don't appear to have mouths or organs, and they are not thought to have been capable of moving, instead absorbing nutrients from the water around them. Most of the larger examples are quite distinct from later life-forms.

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Could the Earth's earliest animals have caused global warming? iStock

Furthermore, it is unclear how Ediacaran lifeforms relate to modern animals, because they largely disappeared with the Cambrian explosion.

Macroorganisms—organisms that can be seen with the unaided eye—from the Ediacaran appear to have been completely replaced by those that evolved during the explosion. And most of the body plans of existing animals derive from creatures that first appeared in the Cambrian fossil record.

This article was updated with comment from Sebastiaan van de Velde.