Timescales for Planetary Formation from Cosmochemistry

Meteorites are relicts of the process of planet‐building in the solar system. Radiometric dating of selected meteorites reveals the timescales associated with planet formation. 100‐km‐scale rocky planetesimals formed within 2–3 Myr of initial collapse of interstellar cloud material, during the T Tauri stage of evolution of the sun. By ∼10 Myr after collapse, coalescence of small bodies had produced terrestrial planets approaching the size of those in our present planetary system.