Ancient Martian Rock Found in Sahara

4.1 billion years. That is the age of Teghaza 001, a Martian meteorite discovered in the Sahara Desert in Mali in 2022. The finding marks the third confirmed ancient sample of Mars material recovered on Earth. Previous estimates suggested most of the Martian surface is older than 3 billion years, yet the standard classes of Martian meteorites are generally 2.4 billion years old or younger.

Yang Liu, a planetary scientist at NASA’s Jet Propulsion Laboratory, led the team that determined the age of the rock. "It’s very old and similar to some of the oldest rocks on Earth," Liu said. The discovery adds to a short list of genuinely ancient Martian fragments, which previously included only Allan Hills 84001, found in Antarctica, and a rock from northwest Africa known as Black Beauty.

The rarity of these samples raises questions about how Mars material reaches Earth. Large impacts launch rocks into space, but not all fragments survive the process. "If the impact hits into loose powder, it may not get cemented to become a rock and fly off Mars’ gravity," Liu said. "So the natural impact already acts as a filter. Weak rocks do not make it off Mars."

This filtering mechanism means the collection of Martian meteorites on Earth is biased. "We don’t fully understand why old Martian rocks are so rare on Earth," Liu said. "Even to date, none of our collected Martian meteorites are similar to what we found on the surface." Black Beauty offers a partial exception because its bulk chemistry matches orbital measurements.

However, Black Beauty is a jumbled mix of soil and small rock fragments. Teghaza 001 is different. It is a single, intact igneous rock. This distinction provides scientists with a clearer view of Mars' ancient crust without the complication of mixed debris.