How water triggered volcanic eruptions 3.1 billion years ago

This was the conclusion reached by an international team of geologists who studied some of the oldest volcanic rocks in Western Australia.

The study has been published in *Nature Communications*.

The researchers found evidence that water from the surface penetrated deep into the Earth’s interior, where it subsequently helped to form magma. Put simply, water did not merely exist in the oceans of the young planet — it may already have been playing a role in the Earth’s internal ‘kitchen’, influencing volcanoes and the growth of continents.

This is significant because 3.1 billion years ago, the Earth was much hotter, and modern plate tectonics probably did not yet function as it does today. Scientists have therefore long debated whether water could have penetrated deep enough at that time to alter the composition of the mantle and trigger magma formation.

Details

Today, water penetrates deep into the Earth at subduction zones. These are places where one tectonic plate slides beneath another. Along with the rocks, water bound within minerals or in altered oceanic crust is also carried downwards. In the mantle, it helps the rocks to melt, and the resulting magma feeds volcanoes — for example, in regions such as the Pacific ‘Ring of Fire’.

But things are more complicated when it comes to the early Earth. Back then, the planet was hotter, and the lithosphere may not have behaved in the same way as modern plates. Therefore, classical subduction may not yet have existed, or may have worked differently. A new study proposes a different mechanism — ‘dripduction’, which is a sort of ‘drip-like sinking’ of the crust.

The idea is this: dense, cooled and water-rich sections of the outer crust may have subsided from time to time and sunk into the hotter mantle. Water would have been carried down with them. As these rocks descended deeper, the water was released and helped to form magma.

How water helps to form magma

At first glance, it sounds strange: water should cool things down, not ‘trigger’ volcanoes. But in geology, water works differently. When it enters hot rock at depth, it lowers the temperature at which that rock begins to melt. Therefore, where the rock would still remain solid without water, the presence of water can cause it to begin melting partially.

This is how magma forms. It rises, feeds volcanoes, solidifies and turns into rock. It is precisely these ancient rocks that geologists are now studying to reconstruct the processes that took place billions of years ago.

According to the study, chemical signatures in the rocks of the Pilbara Craton indicate that the source of these ancient magmas was rich in water and, in this respect, resembled modern volcanic arcs.

Why Australia is important

Rocks of this age are rarely preserved. The Earth’s crust is constantly being recycled: it breaks down, subducts, melts, and changes under pressure and temperature. Therefore, finding well-preserved volcanic rocks over 3 billion years old is a rare stroke of luck.

The Pilbara Craton in Western Australia is one of the few places where the early history of the Earth can be studied. It contains ancient volcanic and sedimentary rocks that provide a rare window into the planet’s past.

Scientists have analysed the chemical ‘fingerprints’ of these rocks. These reveal the conditions under which the magma formed, how much water was present in its source, and what processes may have been taking place deep within the Earth 3.1 billion years ago.

What does this change?

The main conclusion is that the young Earth may already have had a connection between its surface and its deep interior. Water did not simply remain on the surface – it could seep downwards, alter the mantle and help form volcanic rocks.

This does not prove that modern plate tectonics already existed 3.1 billion years ago. The authors are, in fact, more cautious in their conclusions: the Earth did not function in the same way back then as it does now, but some key processes, similar to those seen today, may already have been underway.

This is important for understanding how the continents formed. Water influences the melting of rocks, the composition of magma and the formation of the Earth’s crust. And the continental crust, in turn, is linked to the planet’s long-term habitability: it plays a part in the exchange of substances between the atmosphere, the oceans, the mantle and the biosphere.

Why this is important for the history of Earth

The study does not prove that water ‘created life’ or directly triggered biological evolution. But it helps us understand what the planet was like at a time when life may already have existed or was just becoming established.

If water, the crust and the mantle were already exchanging matter more than 3 billion years ago, then the young Earth was not a static, hot ball, but a dynamic planet. Processes were already at work on it that later became part of the familiar geological system: volcanoes, crustal growth, water cycling and chemical exchange between the surface and the interior.

Background

The modern Earth is constantly ‘recycling’ water. Some of the water remains in the oceans, some enters the atmosphere, and some seeps into the rocks and may subsequently end up deep within the mantle. This cycle affects not only volcanoes, but also the climate, the composition of the atmosphere, the formation of continents and the availability of chemical elements.

In the early history of the Earth, this process may have looked different. Instead of the familiar plate tectonics, more localised and intermittent mechanisms may have been at work — for example, the subduction of dense sections of the crust into the hot mantle. A new study shows that even without modern plate tectonics, water could have reached great depths and influenced magmatism.

Source

Study: “Modern arc-like water content in the source of 3.1-billion-year-old volcanic rocks”, Nature Communications, 2026.