From Dust to Planets -- A Chemical Perspective
Chemical and chronological information preserved in meteorites permits the reconstruction of events and processes in the solar nebula from the formation of the first solids to the accretion of planetary bodies and their subsequent differentiation. The path from a gas-dust cloud to differentiated planets includes intervals of steady evolution interrupted by singular events that dramatically altered this steady path, leading to planetary bodies with distinct chemical compositions and different degrees of internal differentiation. The dominant continuous process in the early Solar System was the cooling of the gas-dust cloud, which caused a steady condensation of elements into solid compounds and a continuous increase in the dust/gas ratio. Planetesimal formation started within less than 1 Ma of Solar System formation and continued for ca. 3 Ma apparently in random regions within the disk. The first planetesimals most likely formed due to streaming instabilities and created gaps in the gas-dust disk that prevented significant element exchange. Later planetesimals formed by accretion of chondrules that had developed in the dust rings by bow shocks. The Earth formed by early accretion of volatile-poor material and a later collision with a Mars-sized volatile richer body after proto-Earth had formed a metal core. This chance event provided the chemical conditions that transformed the Earth into a habitable planet.