Volcanic rocks hold a 2 billion-year chemical diary of our oceans

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: Deep beneath the ocean floor, tectonic plates collide and dive into the mantle. This violent process creates island arcs—chains of volcanoes that act as a geological record. New research reveals these rocks carry a precise chemical fingerprint of seawater chemistry from billions of years ago.

Island arcs form at subduction zones where one tectonic plate dives beneath another. As the oceanic crust descends into the mantle, it undergoes hydrothermal alteration, imprinting it with the specific chemistry of the surrounding seawater. When this plate eventually heats up and melts deep underground, it releases water-rich fluids that carry these chemical signatures into the overlying mantle. This process triggers the melting of the mantle, producing magmas that rise to the surface as island arc basalts.

Strontium isotopes within these volcanic rocks were examined by a study released on October 18, 2024, inside the Proceedings of the National Academy of Sciences. Researchers found that the isotopic ratios in island basalts have varied in tandem with seawater strontium composition over the last 2 billion years. This correlation is driven by changes in how much radiogenic strontium enters the ocean from continents versus unradiogenic strontium from the mantle. Notably, a significant spike in these ratios coincides with a major shift in ocean chemistry during the late Neoproterozoic era, roughly 600 million years ago.

While geochemists have long suspected a link between seawater and island arcs, this study provides a model for how that connection works: seawater strontium is transferred to the arcs through hydrothermal alteration of the ocean floor. By meticulously compiling decades of existing data, researchers proved that these volcanic rocks are not just local geological features; they are interconnected with Earth's broader climatic and geologic shifts. This allows scientists to reconstruct the long-term evolution of our planet's oceans and tectonics by reading the 'fingerprints' left in the deep Earth.

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