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

Significance The crusts of the oldest protoplanets are virtually unknown due to the scarcity of samples. Here, we describe the oldest known lava that crystallized ca. 4,565 Ma ago and formed by partial melting of a chondritic parent body. 26 Al- 26 Mg systematics suggest that the elapsed time between melting and crystallization was significant, on the order of several 10 5 y, probably due to the viscosity of the magma. Although the first protoplanetary crusts were frequently not basaltic, their remains are not detected in the asteroid belt because their parent bodies served as the building blocks for larger rocky bodies or were nearly totally destroyed.