On the evolution of minerals

摘要

The variety of mineral species-has increased since the birth of the Solar System and the development of terrestrial planets. A refreshing view likens the steady rise in mineral diversity to biological evolution. The 94 naturally occurring chemical elements can combine into an endless number of compounds. In nature, however, such compounds come as a few thousand mineral species, each with its own eclectic selection of atoms systematically organized in crystal lattices. Geologists have long used the concepts of'primitive' and 'evolved' rocks to describe the observation that planets such as Earth started out as more or less homogeneous systems, which over time segregated into chemically distinct reservoirs - on Earth, the continents, the oceans and the atmosphere, for example. The rocks that differ most markedly from the initial average planetary composition are 'evolved', and those that never travelled far from their starting composition are 'primitive'. The planets were constructed from building blocks similar to the meteorites that fall to Earth from time to time. The meteorites, in turn, are composed of grains that condensed out of the solar nebula or formed from melt droplets that circled the early Sun. The transition from primary dust to full-scale worlds was followed by a steady increase in mineral species diversity.