Why is it Hot Underground?
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Way back in the Middle Ages, miners began to notice that the deeper they dug into the earth, the toastier it got. Who knows what they made of the heat, but the physicist Lord Kelvin - of temperature fame, naturally - had a theory: Earth started off hot, and has been cooling down ever since, like a baked potato pulled from the oven. What's more, Kelvin was confident this idea would allow him to calculate the age of our potat-- planet... Imagine pulling two recently-baked potatoes out of a freezer - one that's been in there for just one minute, the other for half an hour. The minute-old-one would still feel like a hot potato, while the half-hour frozen spud would have cooled well below the skin — you'd have to poke all the way to the center to feel its residual warm...
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Way back in the Middle Ages, miners began to notice that the deeper they dug into the earth, the toastier it got. Who knows what they made of the heat, but the physicist Lord Kelvin - of temperature fame, naturally - had a theory: Earth started off hot, and has been cooling down ever since, like a baked potato pulled from the oven. What's more, Kelvin was confident this idea would allow him to calculate the age of our potat-- planet... Imagine pulling two recently-baked potatoes out of a freezer - one that's been in there for just one minute, the other for half an hour. The minute-old-one would still feel like a hot potato, while the half-hour frozen spud would have cooled well below the skin — you'd have to poke all the way to the center to feel its residual warm...
