U.S. astronauts Harrison Schmitt and Eugene Cernan gathered approximately 243 pounds (110.4 kg) of soil and rock samples during the Apollo 17 mission in 1972, the last time humans set foot on the moon. These samples were sent back to Earth for additional analysis.
Over fifty years later, zircon crystals found inside a coarse-grained igneous rock fragment Schmitt gathered are helping scientists learn more about the exact age of Earth’s planetary companion and how the moon formed.
Based on studies of the crystals, scientists said on Monday that the moon is around 40 million years older than previously believed, having formed more than 4.46 billion years ago, or within 110 million years of the solar system’s inception.
The main theory on the birth of the moon is that in the tumultuous early history of the solar system, an object the size of Mars named Theia collided with the primordial Earth. This threw molten rock, or lava, into space, creating a debris disk that circled the planet and eventually solidified as the moon. However, pinpointing the precise moment of the moon’s genesis has been difficult.
Following the cooling and solidification of the magma, mineral crystals could develop. The zircon crystals inside Schmitt’s norite rock fragment, which is the earliest known solid to have formed since the massive impact, were dated by the researchers using an approach known as atom probe tomography.
I appreciate that this research was conducted using a sample that was gathered and delivered to Earth 51 years ago. The kinds of analyses we perform now would not have been possible at the time due to the lack of advancements in atom probe tomography, according to cosmochemist Philipp Heck, senior director of research at the Field Museum in Chicago, professor at the University of Chicago, and senior author of the study that was published in the journal Geochemical Perspectives Letters.
It’s interesting to note that zircon crystals are the oldest minerals discovered on Earth, Mars, and the moon. Bidong Zhang, a planetary scientist from UCLA and co-author of the study, said, “Zircon lasts forever, not diamond.”
The zircon-containing rock was mined in the Taurus-Littrow valley, which is located at the southeast tip of Mare Serenitatis, often known as the Sea of Serenity, on the moon. It was later housed at NASA’s Johnson Space Center in Houston.
“Zircons are very hard and tough and survive the breakdown of rocks during weathering,” stated Heck.
Zhang’s work, which was published in 2021, measured the number of uranium and lead atoms in the crystals using an approach known as ion microprobe analysis. Based on the radioactive uranium’s gradual decay to lead, the age of the zircon was determined. If faults existed in the zircon crystal structure, there could be a potential issue with lead atoms, so that age needed to be verified by another approach.
In order to verify the age of the crystals and rule out any lead atom problems, the new study employed atom probe tomography.
“This is an excellent illustration of what the nanoscale, or even atomic scale, can reveal about broad issues,” said Jennika Greer, the primary author of the study and a cosmochemist at the University of Glasgow in Scotland.
With an average orbital distance of roughly 239,000 miles (385,000 km), the moon is little larger than a quarter of our planet’s diameter, measuring about 2,160 miles (3,475 km).
“The enormous impact that created the moon was a catastrophic occurrence for Earth that altered the rotational speed of the planet. Following that, the moon had an impact on slowing down Earth’s spinning speed and stabilizing its rotational axis,” Heck stated. “The formation date of the moon is important as only after that Earth became a habitable planet.”
“The moon helps stabilize Earth’s axis for a stable climate,” Zhang said. “The ocean’s ecosystem is shaped in part by the moon’s gravitational pull.” Human cultures and explorations are inspired by the moon. Furthermore, the moon is viewed by NASA and other space organizations as a springboard for upcoming deep-space missions.