For decades, scientists have been trying to solve one of the great mysteries of the solar system: the exact age of the Moon. If we know today that our natural satellite was formed following a giant collision with the Earth, the dating of this event is a complex and controversial subject. A recent study offers a new and surprising explanation that could reconcile two opposing views of one’s age.
The origin of the Moon: a titanic collision
The formation of the Moon is one of the most fascinating mysteries of the Solar System. The most widely accepted theory, known as the giant impact, suggests that there are approximately 4.5 billion yearsa Mars-sized object called Theia slammed into early Earth. This cataclysmic shock was powerful enough to cause the ejection of large quantities of material from the Earth, primarily from the crust and mantle. This debris then agglomerates under the effect of gravity to form this star which gradually took its current form.
The impact would have had profound consequences not only for the Moon, but also for the Earth. In addition to creating our natural satellite, it would have indeed modified the composition of our planet by enriching its core with iron and nickel and modifying its axial inclination, which would have played a role in stabilizing its climate.
However, the exact dating of this event remains uncertain. Although scientists have largely accepted this giant impact hypothesis, questions persist about the precise chronology of the formation of the Moon.
Scientific methods for estimating the age of the Moon
Geochemists use different methods to determine the age of moon rocks. One of the most common techniques involves analyzing rare minerals found in rocks, such as zircons. These minerals crystallize under very high temperatures and pressures, and their chemical structure allows scientists to date the geological events that marked their formation.
Lunar rock samples collected by the Apollo missions made it possible to determine an age of approximately 4.35 billion yearswhich corresponds to the period of intense warming mentioned by the study. Computer simulations and dynamic models, which take into account the formation of the Solar System, estimate that the Moon was formed approximately 80 million years after its beginning, i.e. approximately 4.4 billion years. These models of orbital dynamics show that it should have formed after the impact with Theia and that the period of formation of the first massive rocks would have been older than indicated by modern lunar samples. This difference in data interpretation has long been a sticking point among scientists.
A recast surface: the key to a hidden age
The key to this enigma could lie in a surprising phenomenon: the remaking of the lunar surface. A new study suggests that there are approximately 4.35 billion yearsthe surface of the Moon would have been completely heated and reshaped, which would have erased the traces of the first giant impacts. This redesign would have modified the appearance of the lunar rocks and distorted estimates of their real age.
The origin of this intense warming lies in the tidal effectssimilar to those which cause tides on Earth. From its formation, the Moon was much closer to our planet than today and the gravitational forces exerted by the latter were much stronger. These forces would have generated sufficiently powerful geological activity on our satellite to melt part of its crust and mantle, and thus reshape its surface. This process would have erased giant impact basins, making dating the first lunar layers difficult.
According to this theory, the lunar rocks analyzed during the Apollo missions, which date back 4.35 billion years, therefore do not record the real age of the Moonbut rather the age of this redesign. This would explain why these rocks appear younger than would be indicated by dynamic models based on the giant Theia impact. So the age of our natural satellite could actually be older than these rocks suggest, and therefore closer to 4.4 billion years old.
