Earth and Planetary Science Grand-Challanges

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.

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