Solar planets started forming 4.6 billion years ago by condensation of the
solar nebula, aggregation of grains to meter size objects, and subsequent
accretion of kilometer size bodies. Terrestrial planets were initially
incandescent objects, particularly Earth after the giant impact that
formed the Moon and left behind a magma ocean. These planets are
still slowly cooling and the process of heat flow from the deep interior
drives, in the case of Earth, plate tectonics that in turn generates
volcanism, earthquakes, and, throughout its evolution, Earth's atmosphere
and magnetic field. The dynamical states of the terrestrial
planets today and in the past contrast sharply. This is caused by the
thermochemical state of their interiors. They all have iron cores and
silicate mantles whose states determine rheological, conductive, and
elastic properties responsible for thermochemical convection and their
evolutionary histories. Earth's mantle extends from about
5-30 km depth to the core-mantle boundary at 2,890 km depth and the core
to 6,300 km. Pressure in the mantle ranges from 3 to 135 GPa and
temperatures, today, range from 1,200 K to ~ 4,000 K. In Earth's center
pressure reaches ~364 GPa and temperature ~ 6,000 K.
