An underwater volcano off Madagascar has erupted chemical remnants from Earth's earliest magma ocean, offering direct evidence of conditions from over 4 billion years ago.
Scientists identified the traces in lava from Fani Maoré, a volcano discovered after an earthquake swarm near Mayotte in May 2018. Eruptions over the next three years caused the island to sink about 20 centimetres.
Researchers led by Catherine Chauvel at the French National Centre for Scientific Research analysed rock samples using a precise method to measure neodymium isotopes. The lava showed a higher ratio of neodymium-142 to neodymium-144 than older volcanic material from Mayotte.
This ratio indicates the presence of ancient mantle rich in bridgmanite, a mineral that crystallised early from the global magma ocean formed after a Mars-sized impact. The findings were published in Nature.
Experts including Claudine Israel and Tim Johnson described the results as a major advance that challenges assumptions about thorough mixing in Earth's mantle over time.