The history of our moon may need to be rewritten. New research on moon dust brought to Earth during NASA’s Apollo 17 mission shows it is at least 4.46 billion years old. This means that Earth’s satellite is 40 million years older than previously thought based on the best measurements.
According to current science, the moon was formed during the formation phase of the solar system from the debris of the primordial Earth’s collision with a Mars-sized celestial body called Theia. But when exactly was that? The new moon dust studies now indicate a minimum age of 4.46 billion years, reports an international research team in the journal ‘Geochemical Perspectives Letters’.
Theia’s collision with primordial Earth was so powerful that large amounts of rock liquefied or even vaporized and were catapulted into space. The moon, which formed from rubble, initially consisted entirely of liquid rock – the so-called magma.
Only when this ‘lunar magma ocean’ had cooled sufficiently at the surface could solid rocks and therefore zircon crystals form there. Because such crystals are virtually immune to subsequent changes, they are particularly suitable for determining age: their age provides a minimum value for the age of the Earth’s satellite.
The team led by Jennika Greer from the University of Glasgow in Great Britain has now examined moon dust for the first time using a so-called tomographic atomic probe. To do this, the researchers first ‘cut’ the zirconium crystals, which are only a few thousandths of a millimeter in size, using an ion beam. The resulting very sharp point makes it possible to remove individual atoms from the sample. “We used an ultraviolet laser to vaporize individual atoms at the tip,” Greer explains.
Age of zircon crystals examined
The vaporized atoms pass through a special analysis device – a mass spectrometer – thus revealing their identity: depending on the weight of the atoms, they move at different speeds. “This allows us to find out, atom by atom, exactly what the crystals are made of,” Greer explains. Researchers can determine the age of the crystal based on the mixing of certain elements in the crystals.
Greer and her colleagues used uranium and lead for this. The background: A certain type of uranium – the isotope uranium-238 – changes into lead through radioactive decay, with a half-life of 4.5 billion years. Since the formation of the solar system, about half of the uranium has been converted into lead.
By accurately measuring the frequency of uranium and lead atoms in the zircon crystals, researchers can determine the age of the crystals. The result: 4.46 billion years. The most accurate measurement to date of another rock sample indicated an age of 4.42 billion years.
Formed in the first 100 million years of the solar system
The crystals that Greer and her colleagues examined are 40 million years older. “It’s an incredible feeling to know that we have found the oldest piece of the moon yet,” Greer said. Because the crystals could not form until the moon’s surface solidified, Earth’s satellite itself must be slightly older. The researchers emphasize that it emerged in the first 100 million years of the solar system.
Phillip Heck from the University of Chicago in the US emphasizes that it is important to know the exact birth date of the moon: “The moon stabilizes the Earth’s rotation axis, is responsible for the length of our days, provides the tides – without the moon there would be life “Very different on earth!” The exact time the moon was formed determines when gravity influenced the development of the Earth.
Source: Krone
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