A 4,565-My-old andesite from an extinct chondritic protoplanet

Area of Science:

• Planetary Science
• Cosmochemistry
• Early Solar System Evolution

Background:

• Protoplanet accretion began in the early Solar System, leading to differentiated bodies.
• Magma ocean cooling and core segregation formed igneous crusts on early protoplanets.
• Understanding primordial crust formation is limited by sample scarcity.

Purpose of the Study:

• To investigate the formation and composition of early planetary crusts.
• To analyze the newly discovered Erg Chech 002 (EC 002) meteorite as a sample of primordial igneous crust.
• To establish the age and origin of the EC 002 meteorite.

Main Methods:

• Analysis of the bulk composition of the EC 002 meteorite.
• Radiometric dating using the Aluminum-26/Magnesium-26 (²⁶Al-²⁶Mg) system.
• Geochemical modeling of partial melting processes.

Main Results:

• EC 002 exhibits an andesite bulk composition, originating from a noncarbonaceous chondritic reservoir.
• It represents the oldest known igneous crust, with a crystallization age of 4,565.0 million years.
• Partial melting occurred at 1,220 °C, indicating parent body accretion around 4,566 million years ago.

Conclusions:

• Andesitic crusts were likely common on early protoplanets.
• The spectral features of EC 002 are unique among known asteroids, suggesting most such bodies are lost.
• These bodies either merged into larger planets or were destroyed, leaving few spectral traces.