How does the temperature of the Earth change as one goes deeper underground?
The temperature increases with depth, but not uniformly throughout. At about 1800 miles, the nickel-iron liquid core is reached (otherwise as known as the "Gutenberg Discontinuity") which extends another 2000 miles to the center of the Earth. The core makes up one third of the mass of the Earth. At the beginning of the core, the pressure is about 10,000 tons! per square inch, and the temperature is about 1,000 degrees Celsius. At the core's center, geologists estimate pressures of 25,000 tons per square inch, and temperatures around 3,000 degrees Celsius. Most of the heat is generated through radioactivity, and it appears that the core has been slowly heating up through the ages as radioactive breakdown continues, and the heat is only very slowly dissipated away.
"The New Intelligent Man's Guide to Science," I. Asimov, Basic Books, Inc., 1965, pg. 108.
The internal heat of the Earth is determined by the rising of temperature with 1 degree at 33 meters deep.
The difference of heat inside of the Earth causes a special movement of terrestrial substance. Increasing and decreasing convection movements are created and the tectonic plates are displaced, creating all sort of consequences in environment(e.g. earthquakes).