Temperatures Pressures and Compositions

The temperature of the Earth rises from about 60°F (20°C) at the surface, to about 8,700°F (4,800°C) in the inner core. Pressure rises from one atmosphere pressure (10-4 GPa) at the surface to 4 million atmospheres (360 GPa) at center (see the sidebar "What Is Pressure?" on page 52). Diamonds, as an example, can be created at only 70,000 to 120 atmospheres (7 to 12 GPa). This corresponds to 125 to 250 miles (200 to 400 km) depth in the Earth.Though people think, from the Earth-surface perspective, that diamonds require impossibly high pressures for their formation, this is only scraping the surface when it comes to the pressures that exist inside the Earth.

The Earth is hotter inside, and heat is convected through the mantle and conducted through the lithosphere into the atmosphere and

What Is Pressure? The simple definition of pressure (p) is that it is force (F) per area (a):

Atmospheric pressure is the most familiar kind of pressure and will be discussed below. Pressure, though, is something felt and witnessed all the time, whenever there is a force being exerted on something. For example, the pressure that a woman's high heel exerts on the foot of a person she stands on is a force (her body being pulled down by Earth's gravity) over an area (the area of the bottom of her heel). The pressure exerted by her heel can be estimated by calculating the force she is exerting with her body in Earth's gravity (which is her weight, here guessed at 130 pounds, or 59 kg, times Earth's gravitational acceleration, 32 ft/sec2, or 9.8 m/sec2) and dividing by the area of the bottom of the high heel (here estimated as one square centimeter):

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