Oxygen enigma: insights could help assess the liveability of other planets


New insights into Earth’s carbon cycle help resolve the longstanding mystery of what caused the rise in atmospheric oxygen levels that presaged the explosion of life.

The new study, published in Nature Geoscience on 10 April, apparently reveals for the first time how the build up of carbon-rich rocks accelerated oxygen production and its release into the atmosphere. Until now the exact nature of how the atmosphere became oxygen-rich has eluded scientists and generated conflicting explanations.

As carbon dioxide is steadily emitted by volcanoes, it ends up entering the ocean and forming rocks like limestone. As global stocks of these rocks build up they can then release their carbon during tectonic processes, including mountain building and metamorphism.

This knowledge was used to build a unique computer model to more accurately chart key changes in the carbon, nutrient and oxygen cycles deep into Earth’s history.

Lead author and biogeochemist Dr Lewis Alcott, Lecturer in Earth Sciences at the University of Bristol, said: “Previously we didn’t have a clear idea of why oxygen rose from very low concentrations to present-day concentrations, as computer models haven’t previously been able to accurately simulate all the possible feedbacks together. This has puzzled scientists for decades and created different theories.”

The discovery indicates that older planets, originating billions of years ago like Earth, may have better prospects to accumulate enough carbon-rich deposits in their crust, which could facilitate rapid recycling of carbon and nutrients for life.

The findings showed this gradual carbon enrichment of the crust results in ever-increasing recycling rates of carbon and various minerals, including the nutrients needed for photosynthesis. This cycle therefore steadily speeds up oxygen production over the passage of Earth’s history.

The research paves the way for future work to unravel the interrelationships between planetary temperature, oxygen, and nutrients.

Co-author Prof Benjamin Mills said: “We have lots of information about distant stars and the size of the planets that orbit them. Soon this could be used to make a prediction of the planet’s potential chemistry, and new advances in telescope technology should let us know if we are correct.”