The formation of the Moon brought water to Earth © Getty Images

The formation of the Moon brought water to Earth

Theia, the Mars-sized planet which collided with the Earth and led to the formation of the Moon, came from the outer Solar System.

The cataclysmic collision which created the Moon brought water to the Earth, allowing life to develop, according to planetologists at the University of Münster, Germany.


The Moon was created 4.4 billion years ago when the Earth collided with a Mars-sized body named Theia. While a large amount of the resulting debris coalesced to form our Moon, some of the material fell to Earth and became part of the mantle, the rocky layer that surrounds the core. The team, led by Dr Gerrit Budde at the Institute of Planetology, made the discovery by investigating the composition of the metal molybdenum found in the Earth’s mantle.

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Atoms of the same element can have different numbers of neutrons, making them heavier or lighter while still having the same chemical properties: these are called isotopes. The composition of molybdenum isotopes is noticeably different in the water-rich ‘carbonaceous’, or carbon-containing, material that originated from the outer Solar System and the dry non-carbon-containing material that originated from the inner Solar System. Before the collision with Theia, the Earth was composed of non-carbon-containing material.

“The molybdenum isotopes allow us to clearly distinguish carbonaceous and non-carbonaceous material, and as such represent a ‘genetic fingerprint’ of material from the outer and inner solar system,” said Budde.

Since the composition of molybdenum isotopes in the mantle lies somewhere in between that of carbon-containing and non-carbon-containing material, the team deduced that the mantle must contain large amounts of material from the outer Solar System. The amount of material brought by the collision with Theia would not only account for the molybdenum, but also for all of the water found on Earth, they say.

“Our approach is unique because, for the first time, it allows us to associate the origin of water on Earth with the formation of the Moon. To put it simply, without the Moon there probably would be no life on Earth,” said Professor Thorsten Kleine.


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