Crater counts indicate that the majority of the Martian surface exceeds 3 billion years in age, yet Martian meteorite samples found on Earth generally tell a younger story. The three primary categories of Martian meteorites—shergottites, nakhlites, and chassignites—are all 2.4 billion years old or younger. Previously, researchers knew of only two genuinely ancient Martian meteorites: Allan Hills 84001, discovered in Antarctica, and a mixed rock from northwest Africa known as Black Beauty. A third ancient specimen has now been identified.
Uncovering an Ancient Martian Rock
A research team headed by Yang Liu, a planetary scientist at NASA’s Jet Propulsion Laboratory, demonstrated that a Martian meteorite named Teghaza 001 formed a minimum of 4.1 billion years ago. The meteorite was discovered in the Sahara Desert in Mali in 2022. According to Liu, the specimen is extremely old and comparable to some of the most ancient rocks found on Earth.
The Impact Filter
Researchers note that the scarcity of ancient Martian rocks on Earth remains incompletely understood, with part of the explanation connected to the ejection process. A massive impact is required to launch a rock off the planet, and not every material withstands the journey. Liu explained that if an impact strikes loose powder, it may fail to cement into a rock capable of escaping the gravity of Mars. The natural impact functions as a filter, preventing weak rocks from leaving the planet.
This dynamic leaves scientists with a biased collection of samples. Liu noted that none of the collected Martian meteorites match what has been observed on the surface. Black Beauty serves as a partial exception because its bulk chemistry aligns with orbital measurements, but it consists of soil mixed with numerous small rock fragments. In contrast, Teghaza 001 is a single, intact igneous rock.
