Europium traces the impact of high temperature hydrothermal systems on the early oceans

Hydrothermal systems have been invoked as a major driver for the evolution of life,
but the impact of hydrothermal fluids on Earth’s ancient oceans and their habitats
remains ambiguous. Europium (Eu) enrichments trace high temperature hydrothermal
fluids in rock archives and may serve as proxy for hydrothermal input into ancient
oceans. Here, we provide Eu abundances from stromatolites and iron formations
between 3.8 and 0.542 billion years (Ga) ago and reconstruct the impact of hydrothermal
systems on shallow and deeper marine environments. Our results document
a continuous decrease in positive Eu anomalies until 2.5 Ga ago, followed by almost
complete disappearance, suggesting a decreasing impact of submarine hydrothermal
systems on ancient oceans. Exceptional positive Eu excursions between 2.8 and 2.6
Ga, and potentially also at 3.5 and 2.2 Ga, are only preserved in deep marine settings and reflect magmatic pulses triggered by elevated upper mantle temperatures. Our results demonstrate the significance of high temperature hydrothermal systems on Archean seawater chemistry with implications for the supply of bio-essential elements. However, life in shallow marine environments
was likely supported by fluxes from emerging continents, at the least from the Neoarchean onwards.