Why is the core of the earth molten?

Molten Earth core vs Solar contribution of energy

• Our planet has a very hot core of molten stuff. How long would it stay hot if the Sun were to go out?

• Answer:

  Hi there! What an interesting question! I think the main thing to understand is whether the sun (or lack of sun) has any appreciable effect on the eventual dissipation of the earth's internal heat. By appreciable I mean, if we are talking 3-4 billion years 'til final cooling (see below), will the lack of the sun change that by a billion or so years? The answer appears to be NO. First, consider where the "liquid" core is located: "Earth has two cores--the inner core and the outer core. The inner core is solid and is about 5100 kilometers down (approximately 3150 miles). Surrounding the inner core is the outer core, which is believed to be liquid, and starts about 2900 kilometers below the surface of the earth (1800 miles)." http://newton.dep.anl.gov/askasci/gen99/gen99175.htm The Earth's crust serves as insulation against heat loss. Heat can only escape through breaks in the crust. There are several ways for this to occur: "With the moon the heat escaped by two mechanisms. One was volcanic activity induced by meteorite impacts. The meteorites penetrated through the crust and into the core... The second way heat escaped was through conduction. Rock is a poor conductor of heat, however, so in larger planetary bodies most of the heat must escape by other means." "Mars is an example of another way internal heat can be lost. Olympus mons, the large Martian volcano is a hot spot, and it probably tapped directly into the core of the planet, and piped the heat in the form of magma directly to the surface." "The third way a planet can lose its heat is to establish convection cells in the mantle. That is, hot, low density material from the lower mantle, heated by the core, flows upward towards the surface where the heat escapes through volcanic activity. The cooled, now denser material then sinks back toward the core to be heated again. This creates a cycle of movement, but it is very slow, only centimeters per year, taking on the order of a billion years of so for a complete cycle." This third way is the way Earth's core loses temperature. In conclusion "... the earth is cooling off, and as time goes by there will be less and less heat to escape until there is none left at all. At that point the earth will die a heat death ... will probably take another 4-5 billion years to loose all its heat -and become a dead planet." But the good news is: "... by that time the sun will expand into its red giant phase and burn the earth to a crisp before that final heat death comes." Note: All of the quotes above are from: The Heat History of the Earth. I urge you to read it in full. I found it fascinating! http://geollab.jmu.edu/Fichter/PlateTect/heathistory.html I hope this helped you understand a little more about our Earth's geology. --K Search term used: "source of heat" earth core