Understanding when oxygen arose in the atmosphere of Earth is important for astrobiologists who study the evolution of life and Earth’s biosphere. An oxygenated atmosphere signaled the arrival of photosynthesis as a major biological pathway on Earth, a change that had profound affects on life.

A popular tool for tracing oxygen in Earth’s geological record has been the chromium (Cr) isotope system. However, a new study shows that molecules called ligands may interfere with the results of this particular chemical tracer. Ligands are common in the environment, and bind to metal atoms to form a larger complex. The new study shows how these molecules could bind with Cr under certain conditions, potentially biasing the results of Cr isotope studies on sedimentary rock. The work highlights important considerations when using the Cr isotope system as a tracer for ancient atmospheric oxygen levels.

For more, read the press release from Georgia Tech here.

The paper, “Redox-independent chromium isotope fractionation induced by ligand-promoted dissolution,” was published in Nature Communications. The research was supported in part by NASA Astrobiology through the Exobiology & Evolutionary Biology program and the NASA Astrobiology Institute.