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The Moon is at least 40 million years older than previously thought, crystals brought back from the Moon by Apollo 17 astronauts have revealed. Earlier, the Moon was assumed to be 4 billion years old, but now, analysis of those crystals has revealed that the Moon is at least 40 million years older than previously thought. The Moon is at least 4.46 billion years old, the new study, published in the journal Geochemical Perspective Letters, has said.
Earlier, scientists thought that a giant object the size of Mars crashed into the Earth about four billion years ago, and the biggest piece that broke off of the early Earth formed the Moon. While it is true that the Earth was hit by a massive object, and this is how the Moon was formed, the assumed time was not correct. Now, the new study has solved the mystery of when the Moon was formed.
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The lunar crystals are the oldest known solids that formed after Earth’s giant impact with a Mars-sized object
Apollo 17, which was launched in 1972, was the last time humans stepped on the Moon.
In a statement released by Field Museum in Chicago, Philipp Heck, a senior author on the paper, said the crystals are the oldest known solids that formed after the giant impact, and since the scientists know how old these crystals are, they serve as an anchor for the lunar chronology.
As part of the study, Heck worked with Jennika Greer, the lead author on the paper. Along with the study’s co-authors, they observed the samples at nanoscales to understand them fully.
The lunar dust brought back by Apollo 17 astronauts has tiny crystals
Apollo 17 astronauts brought back lunar dust to Earth in 1972. The dust has tiny crystals that formed billions of years ago, and these crystals are a tell-tale sign of when the Moon must have formed.
Crystals must have formed after the lunar magma ocean cooled
According to the Field Museum, the energy released from the impact of the Mars-sized object with Earth melted the rock, and formed the Moon’s surface.
Heck said that when the surface was molten like that, zircon crystals could not form and survive, and hence, any crystals on the Moon’s surface must have formed after the lunar magma ocean cooled. He explained that otherwise, the crystals would have been melted, and their chemical signatures would be erased.
According to the study, determining the age of the zircon crystals would reveal the minimum possible age of the Moon because the crystals must have formed after the magma ocean cooled.
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What is atom probe tomography? How did it help the scientists?
As part of the study, the researchers used an analytical method called atom probe tomography, which is a powerful microscopy technique that shows detailed three-dimensional maps revealing the arrangement of atoms within nanoscale volumes of matter. Using this technique, the researchers obtained the age of the oldest known lunar crystal.
In the statement, Greer said that in atom probe tomography, researchers sharpen a piece of lunar sample into a very sharp tip using a focused ion beam microscope, similar to a fancy pencil sharpener. After this, they use UV lasers to evaporate atoms from the surface of that tip. These evaporated atoms are made to travel through a mass spectrometer, which is used to measure the mass-to-charge ratio of molecules. The speed at which the atoms travel through the mass spectrometer tells the researchers how heavy they are, and this tells them what the atoms are made up of.
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Zircon crystals had undergone radioactive decay
The scientists conducted this atom-by-atom analysis using instruments at Northwestern University. They observed that many of the atoms inside the zircon crystals had undergone radioactive decay.
An atom undergoes decay when it has an unstable configuration of protons and neutrons in the nucleus. Due to this unstable configuration, the atom sheds some protons and neutrons, and is transformed into a different element.
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Calculating proportion of different elements can help determine sample’s age
One example is that of uranium decaying into lead. Researchers have deciphered the time it takes for these processes to occur, and hence, by calculating the proportion of different uranium and lead atoms present in a sample, the age of the sample can be determined.
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What is radiometric dating? How did it help them determine the age of the Moon?
Heck explained that in radiometric dating, one counts the number of parent atoms and the number of daughter atoms they have transformed to, and since the transformation time is known, the passage of time can be calculated.
After calculating the proportion of lead isotopes, the researchers concluded that the sample was about 4.46 billion years old, indicating that this must be the age of the Moon.
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Why is it important to know the age of the Moon?
Heck said that it is important to know when the Moon formed because the Moon is an important partner in the planetary system, stabilises the Earth’s rotational axis, is the reason there are 24 hours in a day, and is the reason there are tides. He explained that without the Moon, life on Earth would look different.
The Moon is a part of the natural system that scientists want to better understand, and the study provides a tiny puzzle piece in that whole picture.
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