Earth's first animals triggered global warming

July 2 (UPI) -- Small marine organisms, the world's oldest, had an outsized effect on Earth's oceans and atmosphere, inspiring significant global warming.

When scientists at the University of Exeter analyzed ancient sediment layers, they discovered a decline in ocean oxygen levels between 540 and 520 million years ago.

During this time, small marine organisms began breaking down organic material, a process that eats up oxygen and triggers the release of CO2.

"Like worms in a garden, tiny creatures on the seabed disturb, mix and recycle dead organic material -- a process known as bioturbation," Exeter professor Tim Lenton said in a news release. "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."

Scientists did measure a decrease in oxygen, but they found Earth's earliest animals only barely disturbed the very top layers of seafloor sediment.

"This meant that the animals living in the seafloor at that time were not very active, and did not move very deep into the seabed," said Simon Poulton, a professor at the University of Leeds. "At first sight, these two observations did not seem to add up."

Upon further analysis, however, scientists realized these small communities of marine organisms could have a large impact. Still today, the smallest animals -- like phytoplankton, for example -- can have large impacts on the environment.

"The first bioturbators had a massive impact," Poulton said.

When researchers built and ran a new model to simulate the chemical impacts of these early marine bioturbators, they realized the creatures explain significant shifts in the composition of Earth's atmosphere.

"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 Leeds researcher Benjamin Mills. "We knew that warming occurred at this point in Earth's history, but did not realize it could be driven by animals."

Researchers shared their breakthrough analysis in a new paper, published this week in the journal Nature Communications.

According to the study's authors, the results are a reminder that Earth's inhabitants can alter the planet's climate for the worse. Early global warming made life harder for the planet's earliest creatures and likely explains several mass extinctions during the first 100 million years of animal evolution.