Around 540 to 520 million years ago, the world’s early life forms began to evolve into what scientists consider the first animals. This period, known as the Cambrian explosion, was marked by an increase in the diversity, complexity and abundance of life on Earth.
New research has found that the appearance of these early animals triggered a variety of atmospheric changes, which led to global warming and several mass extinction events over the next 100 million years.
The research, from the Universities of Exeter and Leeds in England, and the University of Antwerp and the Vrije Universiteit Brussel in Belgium, was published on Monday in the journal Nature Communications.
To examine what types of changes may have triggered by the appearance of early animals, the team developed a mathematical model of Earth’s early biogeochemistry. Using this model, the researchers found that the evolution of the animals increased atmospheric carbon in addition to decreasing oxygen levels in both the ocean and atmosphere.
Benjamin Mills, an environmental scientist the University of Leeds, said the team was surprised by the findings: “We knew that warming occurred at this point in Earth history, but did not realise it could be driven by animals.”
As the creatures began to burrow into the seafloor, they stirred up largely undisturbed organic material. Their movements increased the breakdown of organic matter contained in the sediment, resulting in the consumption of oxygen and the production of carbon dioxide.
“Like worms in a garden, tiny creatures on the seabed disturb, mix and recycle dead organic material – a process known as bioturbation,” explained climate scientist Tim Lenton of the University of Exeter.
“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,” he added.
The team noted a link between this part of Earth’s history and the current environmental situation.
“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.”
Dr Sebastiaan van de Velde of the Vrije Universiteit Brussel told The Independent that although there are some similarities in the environmental changes, the timescales in the two periods are very different: “In our study we are talking about tens of millions of years – now we are talking about centuries or not even that.”