A new study has found that the age of the moon is at least 100 million years older than previously thought. Professor Francis Nimmo from the University of California, Santa Cruz, who led the international collaborative research, stated on the 19th that the formation of the moon should be traced back to a time between 4.51 billion years ago and not the known 4.35 billion years ago.
The study's results were published in the international journal Nature on that day. Professor Thorsten Kleine from the University of Münster and researcher Alessandro Morbidelli from the Côte d'Azur Observatory in France also participated as co-authors of the paper.
The timing and origin of the moon have long been a research topic for astronomers. So far, the giant impact hypothesis has become a widely accepted theory. The hypothesis posits that fragments formed by a collision between the early Earth and a protoplanet about the size of Mars coalesced to become today's moon. However, various hypotheses have clashed over when the early Earth collided with the protoplanet. With an increasing number of exploratory missions to the moon and more samples of rocks and dust brought back from the moon, diverse studies have been conducted, and research on the moon's formation period through dating analysis has become active.
When estimating the formation timing of the moon, dating is measured through zircon fragments found in rock and dust samples retrieved from the moon. Zircon fragments contain radioactive isotopes such as uranium, making dating relatively straightforward. Isotopes refer to atoms that have the same atomic number but different masses. By analyzing the ratio at which radioactive isotopes emit radiation over time and transform into other isotopes, their ages can be estimated.
So far, the dating of many zircon fragments brought back from the moon has indicated that they were formed about 4.35 billion years ago. As a result, there have been many estimates of the moon's age at 4.35 billion years. This time, the moon's age has increased.
The moon formed during a massive collision between the early Earth and a protoplanet, whose surface was initially a vast sea of magma. The tremendous energy from the collision caused all the surface rocks to melt into magma. Over time, the magma cooled, resulting in the rocks we see on the moon today.
Until now, the process of the moon's magma sea cooling into rocks was considered a one-time event. However, the research team argued that the zircon fragments used in estimating the moon's formation age were created through transfer. They suggested that the moon was already formed about 100 million years before 4.35 billion years ago and went through a stage where the magma sea became rocks, and then the surface of the moon re-heated, melting the rocks back into magma about 4.35 billion years ago.
The research team identified tidal heating as the cause of the moon's transfer. They noted that tidal heating, caused by the strong gravity of the parent planet reacting with the satellite, occurred on the moon about 4.35 billion years ago. They explained that this was when the orbit of the moon around the Earth changed, leading to tidal heating.
The research team estimated the moon's age based on a new model for determining its chronology. According to their findings, the moon is likely to have formed between 4.43 billion and 4.51 billion years ago, leading to the conclusion that intense volcanic activity resulted in the formation of the crust about 4.35 billion years ago. This suggests that the moon's age, currently estimated at 4.35 billion years, could be shorter by 80 million years or longer by 160 million years.
Professor Nimmo said, "The hypothesis that the moon was formed earlier than is known and underwent transfer due to tidal heating aligns much better with theories of terrestrial planet formation, such as the noble metal content of the Earth's mantle,' and added, 'It makes sense that the moon's surface shows fewer initial collision traces because the evidence of early impacts was erased through transfer.'
References
Nature (2024), DOI : https://doi.org/10.1038/s41586-024-08231-0