Terrestrial planets, chemical evolution

Many asteroids are dry, as evidenced by meteorites in which water is virtually absent. These samples include many classes of chondrites, as well as melted chunks of the crusts, mantles, and cores of differentiated objects. Anhydrous bodies were important building blocks of the rocky terrestrial planets, and their chemical compositions reveal details of processes that occurred within our own planet on a larger scale. The distributions of these asteroids within the solar system also provide insights into their formation and evolution. 

Ringwood, A. E. Chemical evolution of the terrestrial planets. Geochim. cosmochim. Acta 30, 41 (1966). 

There is evidence from chondrites that the solar nebula was well mixed between 0.1 and 10 AU during its first several million years of the evolution, as shown by the homogeneity in concentrations of many isotopes of refractory elements (Boss 2004 Chapter 9). This is likely caused by the evaporation and recondensation of solids in the very hot inner nebula, followed by outward transport due to turbulent diffusion and angular momentum removal. Materials out of which terrestrial planets and asteroids are built have been heated to temperatures above 1300 K and are thus depleted in volatile elements. The inner solar nebula, with some exceptions, does not retain memories of the pristine interstellar medium (ISM) chemical composition (Palme 2001 Trieloff Palme 2006). 

The elements of the chondritic meteorites, and hence of the terrestrial planets, were formed in previous generations of stars. Their relative abundances represent the result of the general chemical evolution of the galaxy, possibly enhanced by recent local additions from one or more specific sources just prior to collapse of the solar nebula —4.56 Gyr ago. A volumetrically minor, but nevertheless highly significant part of this chemical inventory, is comprised of radioactive elements, from which this age estimate is derived. The famihar long-lived radionuclides, such as Th, Rb, K, and others,... 

Abe, Y., 1997. Thermal and chemical evolution of the terrestrial magma ocean. Rhys. Earth Planet. Interior, 100, 27-39. 

Life, with its paired abilities to mutate and to pass those mutations on to subsequent generations, promoted our planet s second stage of chemical evolution and inexorably increased the variety and modified the distribution of chemical substances in Earth s near-surface enviromnent. The innovation of catalytic proteins and polynucleotides, in particular, altered the chemical landscape of our planet. Consequently, for at least three billion years microbial activities have altered the chemistries of Earth s atmosphere and oceans, thus driving the co-evolution of the geo- and biospheres. Atmospheric oxygenation, the innovation of biomineralized skeletons, and the colonization of terrestrial habitats all expanded the influence of life on Earth s surface chemistry. 

Abe Y. (1993) Thermal evolution and chemical differentiation of the terrestrial magma ocean. In Evolution of the Earth and Planets, Geophysical Monograph 74 (eds. E. Takahashi, R. Jeanloz, and D. Rubie). lUGG, American Geophysical Union, Washington, vol. 14, pp. 41-54. 

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