For thousands of years, people have gazed up at the Moon, Earth’s ever-present nightlight.
From the ancient Sumerians to the wise Greeks and story-telling Chinese, everyone has been curious about this glowing disc in the night sky.
If it ever occurred to you—how old is the Moon?, scientists have got your back.
Estimating Moon’s Age Using Samples from Lunar Missions
Before 1609, it was thought that the moon was a smooth, rocky surface, then came Galileo Galilei and his revolutionary telescope, revealing a Moon pockmarked with craters.
Interestingly, the Space race between the United States and Soviet Union in the period of 1960s, led to many groundbreaking space missions, one of them was the missions to the moon.
The United States launched a manned mission to the moon, called “Apollo Mission.” While the Soviet Union focused on an unmanned mission and built a space station for studying the moon.
Moon Rock Samples from Apollo Missions (1969-1972)
The Apollo Mission 8 in 1968 became the first mission with human crew to the moon. It aimed to prove the existing theory however eventually gave way to a new inspiration altogether.
The minerals on the Moon contain less water than rocks of earth, it is rich in minerals that form quickly at high temperatures.
It is interesting to note that the lunar meteorites give more information of the moon than the rocks of the moon from the Apollo mission.
This is because the meteorites come from all over the surface of the Moon while the rocks contain information from only the equator where the Apollo had picked up the rocks.[1]
As the technology has developed and the study of lunar samples got more sophisticated.
| Mission | Site | Sample mass returned | Year |
|---|---|---|---|
| Apollo 11 | Mare Tranquillitatis | 21.55 kg (47.51 lb) | 1969 |
| Apollo 12 | Ocean of Storms | 34.30 kg (75.62 lb) | 1969 |
| Apollo 14 | Fra Mauro formation | 42.80 kg (94.35 lb) | 1971 |
| Apollo 15 | Hadley–Apennine | 76.70 kg (169.10 lb) | 1971 |
| Apollo 16 | Descartes Highlands | 95.20 kg (209.89 lb) | 1972 |
| Apollo 17 | Taurus–Littrow | 110.40 kg (243.40 lb) | 1972 |
Scientists used telescopes to map the Moon’s collection of craters, by the Six Apollo missions during 1969-1972, astronauts brought back a a collection consisting of 2,415 moon rocks, weighing a whopping 842 (~382 Kg) pounds for analysis.
What Do Lunar Samples Tell Us?
The rocks returned from the moon that were studied showed that the chemical and isotopic composition of the moon were similar to that of the earth, this indicates a linked history of the moon with the earth.
If the moon was formed elsewhere and captured by the earth’s gravity then the composition should have been different.
Oxygen isotopes are a key marker for planetary origin. Lunar rocks exhibit identical oxygen isotopic ratios (ratios of 16O, 17O, and 18O) to those found in Earth’s rocks.
This indicates that the Moon and Earth likely formed in the same region of the solar system, as isotopic ratios are considered a “fingerprint” of planetary formation.
Both the Earth and Moon show a depletion in volatile elements (e.g., hydrogen, carbon, and nitrogen) compared to the solar nebula’s primordial material.
This is consistent with high-temperature processes, such as those in a giant impact scenario, where the Moon formed from material ejected into orbit around the Earth.
The Moon shares similar abundances of elements like silicon, aluminum, and magnesium with Earth’s mantle, supporting the hypothesis that the Moon’s material originated from Earth’s outer layers.
Radiometric tests of the Apollo 17 in 1972 rock revealed the age of the rock (not the same as the age of the moon) to be 4.46 billion years old, this age was 40 million years older than the previous rock sample study.
Experts also highlight that the type and proportion of the minerals on the Moon are much different than that of the earth implying that the formation of the moon must be much later after earth was formed.
Studying the Zircons
Zircons are a favorite mineral among scientists as they can withstand weathering of over billions of years and thus, preserving the geo-chemical composition at the time of birth.
They capture the uranium isotopes from the environment as they form, this is more a timer for scientists from the moment of zircon crystallization.
It is notable that the uranium isotopes decay to lead at predictable rates.
Thus, by counting the number of lead and uranium atoms scientists can determine the age of the material from the time zircon hardens from the molten state.
The study of zircons suggests that the moon’s interiors settled into layers around 4.51 Ga or 4.51 billion years ago.[2]
Luna Mission
While the Soviet Luna missions (1970-1976) and lunar meteorites that fell to Earth added even more pieces to the lunar puzzle.
This mission returned with around 300g of samples from the eastern limb of the Moon, and a lunar meteorite collection of about 60 Kg of rocks which were chipped off the moon either by an asteroid/comet strike were pulled to earth’s surface by gravity.
Luna 16 was the first robotic probe to land on the moon and return lunar soil.
After 5 unsuccessful attempts the spacecraft brought back 100 g of lunar rock and dust from Mare Fecunditatis.[3]
Analyzing these samples at the Lunar and Planetary institute indicated that the Moon was formed about ~3.4 billion years ago.[4]
The revelations from the mission speculated a new hypothesis called the giant impact hypothesis.
The Giant Impact Hypothesis
This new impact hypothesis envisioned that at the end of the formation of earth, there could have been a collision with another planet sized body.
This collision produced debris in the earth’s orbit which coalesced into the moon.
From the inspiration of Greek Mythology the impacting planet was named after the Greek Goddess “Theia”, mother of the Moon.
The lunar samples had shown one elemental similarity of Tungsten between Earth and the Moon.
Tungsten crudely hints at the age of the planet’s origin as it is incorporated into the planet’s metallic core, the isotope of the Tungsten is produced during the radioactive decay of Hafnium.
Hafnium is incorporated in the mantle and was prevalent only during the first 60 million years of the solar system.
An alternative concept suggests the formation of a chemically distinct disk. This ”equilibrium” model, the mixing of material, erased the chemical signature of Theia in the moon-forming disk.
About Future Lunar Missions
The latest NASA’s mission Artemis III aims for human landing on the moon south pole in 2025 to precisely estimate the current studies.[5]
NASA aims to “land the first woman and first astronaut of color on the lunar surface”. They are scheduled to stay for a week on the lunar surface to record scientific studies before returning to the earth.
Series of Artemis are planned for a long term ambition of NASA to launch a crewed mission to Mars based on the studies by Artemis.
The name of the mission is inspired from the Greek Goddess and sister of Moon, Artemis and the crewed spacecraft is named Orion after the Greek companion of Artemis, in Greek Mythology.
ISRO’s next lunar mission Chandrayaan 4 scheduled by the end of the decade is aimed to bring back rocks and soil from the moon surface for further studies.
References
- Kerry Lotzof, How did the moon form?, Natural History Museum, https://www.nhm.ac.uk/discover/how-did-the-moon-form.html[↩]
- American Association for the Advancement of Science, Early formation of the Moon 4.51 billion years ago, https://www.science.org/doi/epdf/10.1126/sciadv.1602365[↩]
- Lunar Exploration, Luna 16, https://lunarexploration.esa.int/explore/missions/238?a=317[↩]
- Luna 16 – Lunar and Planetary Institute, https://www.lpi.usra.edu/lunar/samples/atlas/compendium/Luna16Core.pdf[↩]
- Shi En Kim, The Moon is Even Older Than we Thought, National Geography, https://www.nhm.ac.uk/discover/how-did-the-moon-form.html[↩]
