Dear Scott, Chuck, or Steve:
I am in the fourth grade. We are studying the earth, the core, and
volcanos. My question is How did the core get hot in the first place?
Thank you.
Billy Lacey
Hi Billy,
That is a good question. The story is, of course, kind of speculative,
but it goes something like this: The Earth was a young planet just after
the solar system formed, and it was consolidating out of the solar system
nebula of dust and gas. As the young Earth contracted it started to get
denser and denser and as the pressure went up the temperature went up too
(just as when you pump air into your bicycle tire the temperature of the
pump goes up). Additionally, there were still lots of other things flying
around the solar system and many of them came crashing into the Earth as
meteorites. All this also increased the temperature. Finally, there were
a whole bunch of short-lived radioactive isotopes that were incorporated
into the young Earth from the solar-system nebula. As you know, as
elements decay radioactively they give off heat. These three processes
combined to make the whole earth pretty hot.
The story isn't over yet, though. Soon the Earth was hot enough to start
melting, and when this happened the dense things (such as iron) could sink
to the middle of the planet while the less dense things (such as
silicates) could float to the surface. This is why we now have a layered
Earth today. As all that iron "fell" to the center of the earth, it gave
off a whole bunch of energy, and this event (called the iron catastrophe)
generated a whole lot of heat as well.
The Earth hasn't just been cooling off ever since, though. Although the
short-lived radioactive isotopes were mostly used up way back before the
iron catastrophe, the long-lived ones are still around. They are what
keeps the interior hot today, and ultimately are the source of
magmas/lavas at volcanoes.
I hope this makes sense.
Sincerely,
Scott Rowland
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