Burrowing animals may have been pivotal in stabilizing Earth's oxygen

A new study evolution of the first burrowing animals may have played a major role in stabilizing oxygen on Earth.

The scientists have revealed that when the first burrowing animals, which evolved around 540 million years ago, began to mix up the ocean floor's sediments (a process known as bioturbation), their activity came to significantly influence the ocean's phosphorus cycle and as a result, the amount of oxygen in Earth's atmosphere.

Richard Boyle from the Nordic Center for Earth Evolution (NordCEE) at the University of Southern Denmark, said that their research is an attempt to place the spread of animal life in the context of wider biogeochemical cycles, and they conclude that animal activity had a decreasing impact on the global oxygen reservoir and introduced a stabilizing effect on the connection between the oxygen and phosphorus cycles.

The authors hypothesize the following sequence of events: Around 540 million years ago, the evolution of the first burrowing animals significantly increased the extent to which oxygenated waters came into contact with ocean sediments. Exposure to oxygenated conditions caused the bacteria that inhabit such sediments to store phosphate in their cells (something that is observed in modern day experiments).

This caused an increase in phosphorus burial in sediments that had been mixed up by burrowing animals. This in turn triggered decreases in marine phosphate concentrations, productivity, organic carbon burial and ultimately oxygen. Because an oxygen decrease was initiated by something requiring oxygen (i.e. the activity burrowing animals) a net negative feedback loop was created.

The study was published in Nature Geoscience.