Experts are having a new look at the question of exactly where the Earth's water came from.

The conventional theory is that the Earth was too hot when it formed to have water, and that the water came later, delivered by asteroids from the icy outer solar system.

However, international scientists have found that meteorites made up of rock similar to that which formed the Earth contain enough hydrogen to have delivered to Earth at least three times the mass of water in its oceans - suggesting the meteorites that created the Earth may also have brought the water.

Enstatite chondrite meteorites (ECs) – space rocks forged from the nebula that formed the Solar System – are known to be representative of the rocks from which Earth was built.

However, because ECs formed close to the sun, where conditions were too warm for water ice to survive, the meteorites have been assumed to be too dry to account for Earth’s rich reservoirs of water.

As such, Earth’s water is therefore generally thought to be a late addition following the planet’s formation, delivered by more hydrated materials like carbonaceous chondrite meteorites, which originated in the outer solar system where water was more abundant.

But now, researchers have measured the hydrogen content and deuterium/hydrogen (D/H) ratio in thirteen EC meteorites, finding that ECs harbor far more hydrogen than previously assumed.

Following further analyses involving modelling of Earth’s formation that involved mixing of chondrite-like materials, the authors estimate that the EC-like materials that coalesced during the planet’s early formation could have delivered enough hydrogen to the growing proto-Earth to provide at least three times the amount of water in Earth’s present-day oceans.

The D/H ratio and nitrogen isotope compositions of the analysed ECs closely align with those of the Earth’s mantle, supporting claims that the origins of Earth’s water lay within the rocks from which the planet was built.

The authors note they cannot determine exactly when the material was delivered, but it must have been sufficiently late during Earth’s formation.

The study is accessible here.