A moon rock brought back by Apollo 14 astronauts in 1971 may contain a tiny piece of ancient earth (the "felsite clast" identified by the arrow).
Credit: NASA / LPI / USRA / Bellucci et al.
One of Earth's oldest rocks may have been dug up on the moon.
A chunk of material brought back from the lunar surface by Apollo astronauts in 1971 harbors and a tiny piece of Earth, a new study suggests. The Earth fragment was probably blasted off our planet by a strong impact about 4 billion years ago, according to the new research.
"This is an extraordinary finding that helps paint a better picture of the early Earth and the bombardment that altered our planet during the dawn of life," study co-author David Kring, and the Universities Space Research Association (USRA) scientist at the Lunar and Planetary Institute in Houston, said in a statement. (Biologists generally believe that life has reached a foothold on Earth between 4.1 billion and 3.8 billion years ago.) [How the Moon Formed: 5 Wild Theories]
The research team – led by Jeremy Bellucci, of the Swedish Museum of Natural History and Alexander Nemchin, of the Swedish Museum and Curtin University in Australia – analyzed lunar samples collected by members of the Apollo 14 mission, which explored the lunar surface for few days in early February 1971.
The scientists found that one rock contained a 0.08-ounce (2 grams) fragment composed of quartz, feldspar and zircon, all of which are rare on the moon but common here on Earth. Chemical analyzes indicate that the fragment crystallized in an oxidized environment, at temperatures consistent with those found in the near subsurface of early Earth, study team members said.
The available evidence suggests that the fragment crystallized 4.1 billion to 4 billion years ago, about 20 miles (20 kilometers) below Earth's surface, then launched into space by a powerful impact shortly thereafter.
The voyaging Earth rock soon made its way to the moon, which was then about three times closer to our planet than it is today. (The moon is still retreating from us, at a rate of about 1.5 inches, or 3.8 centimeters, per year.) The fragment endured a further trauma on the lunar surface. It was partly melted and probably buried by about 3,9 billion years ago, then excavated by another impact 26 million years ago, researchers said.
This latest collision created the 1,115-foot-wide (340 meters) Cone Crater, whose environs Apollo 14 astronauts Alan Shepard and Edgar Mitchell explored and sampled 47 years ago. (The third Apollo 14 crewmember, Stuart Roosa, stayed in the lunar orbit on the mission's command module.)
An Earth origin for the ancient fragment is not a slam dunk, study team members stressed. However, it is the simplest explanation; and lunar birth would require a rethink of the conditions present in the moon's interior long ago, the researchers said.
The new study was published online Thursday (Jan. 24) in the journal Earth and Planetary Science Letters.
Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018, illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us @Spacedotcom or Facebook. Originally published on Space.com.