Analysis of zircon crystals brought back by Apollo astronauts in 1972 suggests that the Moon is 40 million years older than previously thought. The study, carried out by researchers at the University of Chicago in the US, is the first to use atom probe tomography (APT) to calculate the age of the zircon crystals.
Zircon readily incorporates uranium, excluding lead from the crystal lattice, and is structurally resistant to post-crystallisation thermal alteration. This means that any lead in the samples comes from the radioactive decay of uranium atoms. By measuring the ratio of the two elements, the researchers were able to calculate when the zircon crystals must have originally formed.
APT involves grinding a piece of the sample into a nanotip using a focused ion beam microscope. Ultraviolet lasers are then used to evaporate atoms from the surface of this tip, and mass spectrometry is used to determine the weight and then the composition of the atoms, which indicates how many have undergone radioactive decay. The analysis led the researchers to estimate that the sample was around 4.46 billion years old.
They note that this means that the Moon would have formed in the first 110 million years after the formation of the solar system.
