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Understanding where and in what quantities essential elements for life have existed on Earth's surface helps explain the origin and evolution of life. Phosphorus is one such element, forming the backbone of DNA, RNA, and cellular membranes.

On Earth's surface, phosphorus is primarily preserved in rocks in the form of phosphate minerals. However, these phosphate minerals are generally insoluble. Therefore, scientists have long struggled to answer the question of under what conditions phosphorus could have become concentrated on the early Earth.

Now, a research team including Yuya Tsukamoto and Takeshi Kakegawa from Tohoku University may have found the answer. For the first time, they have uncovered geochemical and mineralogical evidence that submarine hydrothermal alteration may have been a significant source of phosphorus on the early Earth. Their findings are in Geochimica et Cosmochimica Acta.

"We analyzed 3.455-billion-year-old basaltic seafloor rocks in drill core samples recovered from the Pilbara Craton, Western Australia, discovering that phosphorus was significantly leached from the hydrothermally altered rocks compared to the least altered rocks, with further mineralogical analyses indicating that phosphate minerals had undergone dissolution in rocks where phosphorus was depleted explains," explains Tsukamoto.

"In other words, these hydrothermal processes may have released phosphorus from the rocks into the surrounding seawater, enriching early oceans with this essential nutrient."

The team identified that this significant dissolution was caused by two types of hydrothermal fluids: sulfidic and high-temperature fluids, and mildly acidic to alkaline and relatively low-temperature fluids. In particular, the latter fluids are characteristic of the Archean, reflecting a high COâ‚‚ atmosphere at that time.

Calculations indicated that these latter fluids could contain up to 2 mM phosphate, approximately 1,000 times higher than modern seawater concentrations. Furthermore, calculations based on the study's analytical results suggested that the annual flux of phosphorus from Archean submarine hydrothermal fluids could have been comparable to that supplied to the modern ocean by continental weathering.

"Importantly, this study provides direct evidence that submarine hydrothermal activity leached phosphorus from seafloor basaltic rocks and quantifies the potential phosphorus flux from these hydrothermal systems to the early ocean," adds Tsukamoto.

"Our findings demonstrate that hydrothermal systems could have locally supplied sufficient phosphorus to support early microbial ecosystems. These environments may have served as cradles for early life and played a significant role in the origin and evolution of life."

The study also highlights the potential impact of hydrothermal fields not only on the seafloor but also in terrestrial settings such as hot springs. Future research on phosphate behavior in hydrothermally altered rocks through time will further reveal shifts in phosphorus cycles on the early Earth.