Subsurface temperature

The more down, below the earth's surface temperature has increased or the heat. The heat comes from within the earth resulting from the decay reaction of radioactive elements like uranium and potassium. The same nuclear reactions are still happening on the sun and the stars are scattered in the universe. This reaction produces heat up to millions of degrees Celsius. The surface of the earth at the beginning of the formation also has a tremendous heat. But after a period of billions of years, Earth's temperature continues to decline and now the remnants of the nuclear reaction contained only the core section of the earth. At a depth of 10,000 meters or 33,000 feet, the resulting heat energy could reach 50,000 times the amount of energy reserves of petroleum and natural gas are still stored in the world. This is thea source of of geothermal energy .