1.4 billion-year-old salt crystals reveal Earth’s ancient oxygen spike

Researchers from Rensselaer Polytechnic Institute analyzed 1.4-billion-year-old halite (salt) crystals from ancient subtropical lakes in present-day Ontario, Canada, which trapped microscopic bubbles of air and droplets of brine. These "fluid inclusions" preserved a direct record of Earth's Mesoproterozoic atmosphere, extending the atmospheric record by over a billion years. By developing custom laboratory techniques to correct for chemical interactions between gases and the trapped brine, the team obtained accurate measurements of ancient atmospheric gases, including oxygen and carbon dioxide. Their findings challenge the notion of the Mesoproterozoic era (1.8 to 0.8 billion years ago) as the "Boring Billion" by revealing a transient oxygenation event with oxygen levels at about 3.7% of modern concentrations—potentially sufficient to support complex multicellular life, which appeared much later. Carbon dioxide levels were found to be roughly ten times higher than today, explaining the warm, ice-free climate