A team of researchers from the University of Göttingen and the Max Planck Institute for Solar System Research (MPS) has just given an unexpected twist to what we knew about the origin of the Moon and, incidentally, also the presence … of water on Earth.
Until now, in fact, the most accepted idea was that our satellite was formed from the fragments of a protoplanet called Theia, which about 4 billion years ago was involved in a gigantic collision with the primitive Earth. But according to the new study, just published in ‘Proceedings of the National Academy of Sciences’ (PNAS)it was not the pieces of Theia that ended up forming the Moon, but the materials from the Earth’s mantle itself expelled into space after the tremendous impact. Theia, for her part, would have had a minimal contribution.
A metal cannonball
The study also supports the idea that Earth’s water did not arrive after that collision and on the back of comets and asteroids, but could have ‘landed’ on our world much earlier than previously thought.
To reach these conclusions, the researchers analyzed oxygen isotopes in 14 lunar samples and made up to 191 measurements of various terrestrial minerals. To do this, they used an improved version of a technique called ‘laser fluorination’, which extracts oxygen from rock samples using a laser. The analyzes revealed an exceptionally close match between the Earth and Moon samples for a specific isotope known as oxygen-17 (17O). This striking similarity so baffled scientists that they even coined the term ‘isotope crisis’ to describe the difficulty of explaining it.
«A possible explanation – says Andreas Pack, co-author of the study – is that Theia lost its rocky mantle in previous collisions and then crashed into the early Earth like a metallic cannonball. If this were the case, Theia would today be part of the Earth’s core and the Moon would have formed from material expelled from the Earth’s mantle. “Which would explain the similarity in the composition of the Earth and the Moon.”
Origin of Earth’s water
The data obtained also provide insights into the history of water on Earth: the dominant opinion is that the liquid element reached our planet quite some time after the formation of the Moon and due to a series of additional impacts during the so-called ‘Water Event’. the Late Layer’. Since the Earth was hit much more frequently by these impacts than the Moon, there should also be a measurable difference between oxygen isotopes, depending on the materials that impacted.
«However – points out Meike Fischer, first author of the article – the new data shows that this is not the case, so many types of meteorites can be ruled out as the cause of that event. “Our data can be explained particularly well by a single class of meteorites called ‘enstatite chondrites’: they are isotopically similar to Earth and contain enough water to be solely responsible for our planet’s water.”
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