Oldest Earth rock on the Moon

The oldest Earth rock found on the Moon came to light in March 2019. The study, published in Earth and Planetary Science Letters, focuses on a 4.011-billion-year‑old chunk of felsite that was collected during the Apollo 14 mission in 1971. Its composition of quartz, zircon and feldspar (all of which are extremely rare lunar minerals) and high oxygen content indicate that it most likely formed on Earth rather than being a native Moon rock. It is believed that the felsite may have been blasted up to our planet’s satellite after a powerful impact event.

This makes this specimen among the oldest of any rocks ever discovered, though this field is notoriously complicated as there is no universally accepted technique for ageing rocks, and it’s hard to know whether you’re ageing a specific rock or the material that it formed from (i.e., “the precursor”).

When it comes to the oldest rock, one contender is bedrock taken from the Nuvvuagittuq Greenstone Belt on the shore of Hudson Bay in Quebec, Canada, dated at 4.28 billion years old using isotopic techniques. Another is gneiss taken from an island in the Acasta River in Canada’s Northwest Territories, with an upper age limit of 4.03 billion years calculated with radiometric dating.

In terms of rock fragments, pieces of zircon from the Jack Hills region of Western Australia have been estimated at 4.3–4.4 billion years old. At only about the width of a human hair across, though, these crystals are not considered “rocks”, but rather chips off older blocks, making them the oldest fragments of Earth. Although their precise age is debated, a 2014 paper that used atom‑probe tomography to try to settle the argument determined them to be 4.374 billion years old (give or take 6 million years); this would make them only around 160 million years younger than Earth itself.