Heat from the planet formation process, radioactive decay of some elements and friction between layers causes the Earth’s core to maintain extremely high temperatures after 4.5 billion years.
In the center of the Earth, the temperature reaches 5,200 degrees Celsius, nearly as hot as the surface of the Sun. What maintains this hellish temperature are forces that have existed for billions of years, according to IFL Science. The Earth’s core is divided into two distinct regions: the outer core, which is mainly composed of molten iron and nickel, and the inner core, which is essentially a solid sphere as large as the Moon, made of two metals.
Even though the temperature inside the core is extreme, we cannot feel the heat at the surface except through volcanoes and geothermal springs. The outer core begins at a depth of 2,889 km below the Earth’s crust. Between the surface of the crust and the outer core there is a lot of material, the mantle contains rocks that absorb and dissipate heat. In fact, there is no way to directly measure heat. Because it is impossible to send probes or people deep underground, scientists calculate temperatures by studying how iron and iron-rich compounds melt under high pressure. By determining the melt temperature, they were able to deduce the temperature at the core.
Some of this heat is a vestige from the past, associated with the birth of the planet. The ground will cool rapidly while the core is the last area to cool down. Earth was born about 4.5 billion years ago when gravity condensed matter from a cloud of hot gas and particles surrounding the young Sun. As the molten sphere cools, the outer layer hardens like candle wax and forms a shell. However, the coating still retains some of the heat and continues to cool gradually.
A 2011 study estimated that heat left over from planet formation accounts for nearly half of the heat in Earth’s interior. The remainder comes from radioactive decay of uranium-238 and thorium-232 in the planet’s core, accounting for about 54%. Finally, there is heat from the friction process caused by the movement of hard and liquid layers under enormous pressure.
Heat in the Earth’s interior is important to the surface because it is the main driving force behind tectonic plates, causing them to move around, creating or destroying continents. Researchers predict that the Earth’s core will cool and solidify 91 billion years after the Sun dies.