BioturbationThe appearance of animals on Earth after 3 billion years of evolution in microbial ecosystems is often claimed to be a result of rising O2 levels on Earth. However, evolving animal ecosystems may in fact have lowered O2 levels.

In a recent study (Boyle et al. 2014), we show that the animal invasion of the seafloor at the Ediacaran/Cambrian boundary (~542 Ma) affected the global marine phosphorous and carbon cycles through bioturbation. Ultimately, this resulted in lowering of atmospheric O2 levels on a million year time scale. As O2 levels decreased, bioturbation decreased as well. This mechanism explains why O2 levels have remained stable after the emergence of motile animals. To put it shortly, early animal ecosystems took stewardship over O2 regulation on Earth!

References:

Boyle et al. Nature Geoscience (2014): Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation

Filip Meysman News & Views Nature: Oxygen burrowed away

Interview and news in Science: Ancient worms may have saved Earth