Earth’s Oldest Rock Found — It was Hiding on the Moon!

Big Bertha is the oldest Earth rock ever discovered, and it was found on the Moon, among the samples returned from the Apollo 14 mission. Researchers estimate the crystal-rich rock is around four billion years old.

Apollo 14 launched January 31, 1971, on a nine-day journey to bring astronauts Alan Shepard and Edgar Mitchell to the lunar surface. Stuart Roosa orbited above the Moon, piloting the command module, Kitty Hawk. After touching down in the Fra Mauro formation (the planned destination for the unsuccessful Apollo 13 mission), astronauts collected material from the Moon, including Big Bertha.

“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,” said David Kring of the Lunar and Planetary Institute.

The complete Big Bertha specimen, returned from the Moon by the Apollo 14 crew in 1971. Credit: NASA/Johnson Space Center

Big Bertha likely crystallized 20 kilometers (12.5 miles) under the crust of the Earth, before being jettisoned out into space four billion years ago. At that time, the Moon was only one-third as far from our planet as it is today. The rock collided with our planetary companion, and the region in which it landed was then impacted by a second collision event 3.9 billion years ago, burying the rock, and melding it with native materials found there. Finally, 26 million years before our time, another body struck that area of the Moon, creating the Cone Crater, raising Big Bertha to the surface, where it was found by astronauts from Apollo 14 on their mission 48 years ago.

When Big Bertha was returned from the Moon, the rock measured 23 centimeters (nine inches) across, and weighed 9 kilograms (20 pounds). The sample analyzed in this study, however, is small, weighing just two grams (one-seventh of an ounce, roughly the weight of half a teaspoon of sugar). Researchers found it contains quartz, feldspar, and zircon. Although these materials are common on Earth, they are rare on the Moon.

The fragment of Big Bertha which was analyzed, revealing its terrestrial origin. Credit: Universities Space Research Association (USRA)

The astronauts who landed with Apollo 14 collected 42 kilograms (92.6 pounds) of samples from the surface of the Moon. Most of these are breccias (rocks composed of diverse older material). This landing spot was originally selected as the destination for Apollo 13, since astronomers knew it was an area where astronauts could find both young and old rocks, due to the geological history of the region.

“Prior to the abort of Apollo 13, Apollo 14 was targeted to land in the Littrow region of Mare Serenitatis, where the objective was to study young, pyroclastic volcanic deposits. Following the Apollo 13 abort, it was decided to retarget Apollo 14 to the Fra Mauro site, which was regarded as scientifically more important than the Littrow site,” The Lunar and Planetary Institute explains on their website.

Alan Shepard, seen as he set up equipment on the Moon, during the Apollo 14 mission. Credit: NASA

The possibility still exists that Big Bertha formed on the Moon, but that theory would require that the rock crystallized deep under the lunar surface, and was transported to the surface by unknown processes. The simplest explanation is that Big Bertha is, in fact, of terrestrial origin.

Apollo 14 may be best known as the mission where Alan Shepard hit golf balls on the Moon, using a makeshift club.