The most-ancient samples

Meteorites present us with tantalizing evidence concerning the origin of the solar system and they provide us with the best evidence of the time when the solar system formed. However, as the citizens of Ensisheim, Alsace, noted about the meteorite that fell there in 1492, “many know much about this stone, everyone knows something, but no one knows quite enough” [1].

Some of the grains in primitive chondrites retain a memory of presolar conditions. The refractory inclusions in chondrites tell us of the earliest recorded events in the solar system. Even though the CI carbonaceous chondrites were somewhat altered in an aqueous environment, the elemental abundances of these meteorites resemble those of solar photospheric spectra for the nongaseous elements, providing a basis for estimating the composition of the solar nebula [2]. Much chemical processing occurred very early, which resulted in (i) the formation of refractory inclusions, chondrules; (ii) the separation of metal, sulfide, and silicate phases; and (iii) the depletion of volatile elements in the inner parts of the solar nebula. Differentiated meteorites such as the eucrites and the iron meteorites tell us of the existence of both planetesimals and of heat sources that induced melting. This differentiation also occurred very early, with the production of true igneous rocks close to T0.

Even after the cessation of the turbulent conditions that accompanied meteoritic and planetary formation, meteorites that reach the Earth have had an interesting dynamical history.