Toxic oceans may have delayed spread of complex life

Feb 28, Earth/Earth Sciences


The research, published online this week in the journal Nature Communications, considers the composition of the oceans 550-700 million years ago and shows that oxygen-poor toxic conditions, which may have delayed the establishment of , were controlled by the biological availability of nitrogen.

In contrast to modern oceans, data from indicates that the of the contained little oxygen, and flipped between an iron-rich state and a toxic hydrogen-sulphide-rich state. The latter toxic sulphidic state is caused by bacteria that survive in low oxygen and low conditions. The study shows how bacteria using nitrate in their metabolism would have displaced the less energetically efficient bacteria that produce sulphide – meaning that the presence of nitrate in the oceans prevented build-up of the toxic sulphidic state.



Today, an abundance of nitrate, in the context of an oxygenated , prevents a reversion to the inhospitable environment that inhibited early life. Determining how the Earth's oceans have established long-term stability helps us to understand how modern oceans interact with life and also sheds light on the sensitivity of oceans to changes in composition.

Provided by University of Exeter
