Halogen ratios in crustal fluids through time—Proxies for the emergence of aerobic life?

Abstract Halogens (Cl, Br, I) are exceptional provenance tracers in crustal fluids because their ratios not strongly altered during most fluid-rock interaction processes. The halogen systematics of metamorphic particular interest such key drivers crustal-scale element fluxes and ore formation orogenic belts, but they remain poorly studied due to analytical challenges. We present novel triple-halogen laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) fluid-inclusion data from systems ranging age Archean Phanerozoic. Our results show that the signatures Phanerozoic controlled by variable degrees organic-matter source rocks, leading increased I/Cl decreased Br/I relative seawater. By contrast, organic matter–rich rocks have low very high ratios, distinctly different any known fluid signature. propose these nevertheless consistent with dominantly prokaryotic lifeforms did yet produce iodine-bearing metabolites. This prevented biosequestration accumulation iodine-rich matter sediments imposed onto entirely unlike those younger fluids.