Fluid inclusions: tiny windows into global paleo-environments.

Geochemical traces of past environments are preserved in the geological record. Although secondary processes often erase this information, fluid inclusions in hydrothermal minerals act as time capsules for reconstructing the evolution of Earth's atmosphere and oceans, including the Great Oxidation Event (GOE). Here, we summarize decades of insights from analyses of ancient fluids in hydrothermal minerals worldwide. These geochemical constraints illuminate the formation of the atmosphere, its evolution through volcanism, escape to space, and subduction. Reconstructions of past atmospheric noble gas and nitrogen compositions, along with ocean salinity, reveal major steps in our planet's evolution. They shed unique light on long-standing questions, including Earth's climate under a faint young Sun, the missing Xe paradox, the cause and timing of oxygenation, the emergence of continents, and the flourishing of life. A refined understanding of the physical mechanisms driving xenon isotopic evolution prior to the GOE may further constrain links between early solar activity and early environmental changes.