How Earth acquired the water that eventually made its oceans remains one of planetary science's major questions.
A new experimental study offers evidence for one possible pathway: water can form chemically inside the hot, hydrogen-rich atmosphere surrounding a young rocky planet as it grows by capturing small silicate-rich pebbles.
Editorial Insight
Key Highlights
Important points readers should notice.
Issue/Event: Researchers experimentally tested a possible water-formation pathway during rocky-planet growth.
Location: Laboratory experiment; implications extend to terrestrial planet formation.
Authority/Organisation: International planetary-science research team.
Action Taken: Scientists simulated reactions involving dry silicate pebbles and a hydrogen-rich planetary atmosphere.
Impact: The results provide evidence for a possible in-situ source of water during early planet formation.
Researchers experimentally recreated conditions relevant to planetary formation and found that reactions between hydrogen and oxygen-bearing minerals can generate water at high temperatures.
The study was published in Nature Geoscience on September 24, 2026.
The key idea: dry material can still make water
Editorial Analysis
Why This Matters
The study changes the question from simply “Where did Earth's water come from?” to a broader one: “How much water could have been chemically produced while Earth was forming?” If similar reactions occurred widely around young rocky planets, water could potentially become available earlier in planetary development than previously assumed by models that depend primarily on delivery from external water-rich bodies. The mechanism could therefore be relevant not only to Earth but also to the study of potentially habitable rocky planets around other stars.
The research addresses an important distinction in the early history of rocky planets.
Water does not necessarily have to arrive as already-formed ice or hydrated minerals.
When a young rocky planet captures millimetre-to-centimetre-sized silicate pebbles, those particles can pass through a hot atmosphere containing abundant hydrogen.
Under the right temperature and chemical conditions, oxygen within the silicate material can react with hydrogen and produce water.
The researchers tested this process experimentally rather than relying only on computer modelling.
Why a hydrogen-rich atmosphere matters
Young rocky planets can temporarily develop atmospheres containing large amounts of hydrogen while they are still growing.
Hydrogen is highly reactive under suitable conditions. If oxygen-bearing minerals are introduced into such an atmosphere at sufficiently high temperatures, chemical reactions can alter the material and produce water.
This creates a potential source of water during the planet-building stage itself.
Does this prove Earth's oceans formed this way?
No.
The study demonstrates a physically plausible water-forming mechanism under experimentally tested conditions. It does not establish that this was the dominant source of Earth's oceans.
Earth's actual water inventory could involve multiple processes, including material incorporated during planetary formation and later delivery or redistribution.
The new experiment adds another mechanism that planetary scientists can evaluate when reconstructing Earth's early history.
Why pebbles matter in planet formation
Planet formation is not simply a process in which large objects collide randomly.
Small solid particles can grow, move through young planetary systems and become incorporated into larger bodies.
The study specifically examines millimetre-to-centimetre-scale silicate pebbles entering the atmosphere of a growing terrestrial planet.
That makes the chemistry relevant to the period when rocky planets were accumulating their mass.
