A Martian meteorite that formed ≳4.1 billion years ago samples Mars' early crust and mantle.

Teghaza 001 (Teg 001) is a slowly cooled Martian igneous rock that formed at least 4.1 billion years ago and samples ancient crust.

• Why it matters: Most Martian meteorites are younger than the ancient surface rocks, limiting how well they reflect Mars’ early crust and mantle evolution.
• What they did: The team analyzed Teg 001’s composition, mineralogy, and texture, then used bulk and mineral-specific oxygen isotope measurements to test for fluid-related alteration.
• The result: Teg 001 is linked to a geochemically distinct mantle source with primordial composition and shows aqueous alteration from 18 O-enriched fluids prior to impact ejection.

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