Today, the deepest hole ever created by humankind lies beneath the tower enclosing Kola’s drill. A number of boreholes split from the central branch, but the deepest is designated “SG-3,” a hole about nine inches wide which snakes over 12.262 kilometers (7.5 miles) into the Earth’s crust. The drill spent twenty-four years chewing its way to that depth, until its progress was finally halted in 1994, about 2.7 kilometers (1.7 miles) short of its 15,000-meter goal.
The core of the earth, which is about 4000 miles below the surface, is where geothermal energy is generated. Temperatures that can sometimes be even hotter than the surface of the sun are produced incessantly within the earth by radioactive particles decaying slowly, a process that occurs in all rocks. The earth is made up of a number of layers: the core; the mantle; and the crust.
- The Core: The core of the earth itself comprises two layers - an outer layer which is made up of extremely hot molten rock, known as magma, and an inner core made of solid iron.
- The Mantle: This layer, which comprises rock and magma, envelopes the core and has a thickness of around 1800 miles.
- The Crust: The earth's outermost layer is called the crust, which basically comprises all the land that makes up the floor of the oceans and the continents. The crust is about 15-35 miles in thickness on the continents and of about 3-5 miles in thickness beneath the oceans.
The crust of the earth is made up of several broken pieces, which are known as plates. The hot magma from deep down below rises up close to the surface of the earth at the junctures of these plates. These are the places where volcanoes are formed. The lava that spews from volcanoes is made up partly of magma. The heat from this magma is absorbed by the water and rocks that occur deep beneath the earth's surface. The temperature of the water and the rocks get increasingly hotter the deeper down you go below the earth's surface.
People all over the world have been using geothermal energy to heat their homes by digging wells that go down very deep and pumping up the hot steam or water to the surface.