To arrive at these conclusions, the team analyzed oxygen isotopes from 14 lunar samples and conducted 191 measurements on Earth's minerals. Isotopes, which are variations of elements with different nuclear weights, provide critical clues about planetary formation. The researchers employed an advanced version of "laser fluorination," a technique that uses a laser to release oxygen from rock samples. The results revealed striking similarities in the isotopic composition of oxygen-17 (17O) in samples from both Earth and the Moon. This similarity addresses a longstanding issue in cosmochemistry, often referred to as the "isotope crisis."

Professor Andreas Pack, Managing Director of Gottingen University's Geoscience Centre and Head of the Geochemistry and Isotope Geology Division, explained the implications: "One explanation is that Theia lost its rocky mantle in earlier collisions and then slammed into the early Earth like a metallic cannonball. If this were the case, Theia would now form part of the Earth's core, and the Moon would have formed from ejected material from the Earth's mantle. This would explain the similarity in the composition of the Earth and the Moon."

The research also sheds light on the history of water on Earth. A common hypothesis suggests that water arrived after the Moon's formation, during a period known as the "Late Veneer Event," when Earth was bombarded by a series of impacts. These impacts, being more frequent on Earth than the Moon, should have resulted in measurable differences in oxygen isotopes between the two bodies. However, the new data indicate that such differences do not exist, challenging the late veneer hypothesis.

First author Meike Fischer, who conducted the research at the Max Planck Institute for Solar System Research, elaborated: "Our data can be explained particularly well by a class of meteorites called 'enstatite chondrites': they are isotopically similar to the Earth and contain enough water to be solely responsible for the Earth's water." This finding rules out many other types of meteorites as the source of the "late veneer."