10 - Comparative Planetary Evolution

Abstract

This chapter focuses on the Earth as a member of the solar system by comparing it to other planets and emphasizing on its uniqueness. Plate tectonics, continents, oceans, and the presence of free oxygen in the terrestrial atmosphere are unique to Earth. Most data suggest that planets originated by the condensation and accretion of a gaseous solar nebula in which the Sun forms at the center. The age of the universe is of the order of 13.7 Ga, thus the formation of the solar system at about 4.6 Ga is a relatively recent event. Since detailed planetary formation in other gaseous nebulae cannot be observed, a variety of indirect evidence to reconstruct the conditions under which the planets in the solar system formed prove to be helpful. Geophysical and geochemical data provide the most important constraints. The interiors of planets are not accessible for sampling therefore planetary motions are studied through meteorites. Most scientists now agree on the fact that the solar system formed from a gaseous dust cloud, known as the solar nebula. This chapter reviews members of the solar system, with a special comparison of Earth with its sister planet Venus. It also discusses satellites and planetary rings, meteorites, planetary crusts, comparative planetary evolution, and extra solar planets.