• Question: Why is the Earth's core hot? What caused it to heat up? Is it still heating, or now cooling?

    Asked by beckybeth to David, Luna, Mark, Melanie, Probash on 23 Mar 2011 in Categories: .
    • Photo: Luna Munoz

      Luna Munoz answered on 23 Mar 2011:

      It has remained hot since when it was formed billions of years ago. Also, there is friction and decay from radioactive elements that keep it hot. The activity of the plates moving like in earthquakes would make the earth cool a bit, but I don’t think we have to worry about it cooling too much. I think David would know more about it.

    • Photo: David Pyle

      David Pyle answered on 23 Mar 2011:

      Good question! Earth’s metallic core became hot as it formed, early in Earth history – probably within about 30 – 50 million years of the formation of the Earth.

      As Earth grew by the addition of meteorites it would have started to warm up, mainly from heat from the decay of radioactive elements plus heat from the kinetic energy of meteorite impacts. Soon, parts of the Earth became hot enough for the iron to start to melt; and as it did so, these dense blobs of molten metal sank under gravity towards the cente of the planet. As they sank, they heated up further still (conversion of potential energy into heat), and very quickly the Earth had a molten iron core.

      Ever since then, the core has been cooling. Today, the inner core is solid (at 6000 – 7000 K!)- and as the Earth continues to cool the inner core will continue to grow, due to the slow freezing of the liquid outer core.

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