Scientists stunned to find Earth’s oldest rock in strangest of places

25 Jan 2019

Image: © Arvin/

After digging through lunar samples brought back by astronauts, scientists were surprised to find what could be Earth’s oldest rock.

The theory that the moon was once a part of Earth and was cast off by a massive cosmic collision is not new, but recent findings show that, strangely, a piece of Earth may have managed to find its way to the moon after this event.

Publishing its findings to Earth and Planetary Science Letters, an international team of scientists associated with the Center for Lunar Science and Exploration revealed that Earth’s oldest rock has been discovered in a lunar sample returned to our planet by Apollo 14 astronauts.

By sifting through the small amounts of moon sample, the team was stunned to find evidence that the 4bn-year-old rock was launched from Earth by a large impacting asteroid or comet. This impact would have jettisoned material through Earth’s infant atmosphere and eventually found its way to the moon.

You might be thinking that’s an awful long way for a rock to travel, even if was the result of a colossal strike, but at this time the moon was three times closer to Earth than it is now. After its arrival, the rock got mixed in with other lunar surface materials into one sample.

Black and white close-up of Earth's oldest rock fragment.

Earth’s oldest rock fragment. Image: Lunar and Planetary Society

‘An extraordinary find’

The rock fragment that led to this discovery weighs just 2g and comprises quartz, feldspar and zircon, elements that would be highly unusual on the moon. Chemical analysis later showed that it crystallised in a terrestrial-like oxidised system at terrestrial temperatures, rather than in the reducing and higher temperature conditions that are characteristic of the moon.

There is a chance that the sample didn’t come from Earth and that it actually crystallised on the moon; however, this would require it to have formed at tremendous depths in the lunar mantle where very different rock compositions are anticipated. This led the team to say with a high degree of certainty that it came from Earth.

The rock is considered a relic of an intense period of bombardment that shaped the solar system during its first billion years, after which the moon was only affected by small and less frequent events.

Principal investigator of the mission, Dr David A Kring, admitted that these findings will prove controversial, as being the first find of its kind means it will be put under more scrutiny in order to locate similar samples. These, he believes, will eventually be found.

“It is an extraordinary find that helps paint a better picture of early Earth and the bombardment that modified our planet during the dawn of life,” he said.

Colm Gorey was a senior journalist with Silicon Republic