Answer 1:
First, let’s talk about heat: a hot object has
more energy with a cold object, and will share its
energy if the two are touching. They can share
energy in three ways, from fastest to slowest:
1 – direct contact
2 – indirect contact, like heating the air around
the objects
3 – radiation of light (This doesn’t need air to
work.)
When the Earth was formed, it was very hot, with
molten rock at the surface of the planet. There
wasn’t a quick way for the Earth to cool, though,
since it wasn’t in direct contact with something
cooler and there’s no air in space to absorb the
energy. Instead, it could only lose heat by
radiation, which is a slow process. So, the
Earth cooled slowly and a solid crust formed that
was cooler than the inside. This layer also
insulates the molten rock below, by preventing
heat from escaping by radiation. Instead, the
molten rock has to heat the crust and atmosphere,
which then radiates the heat into space. So, the
Earth is cooling from the outside in but this
process is very slow.
You can observe this process the next time you
have soup. When you pour hot soup into a cold
bowl, the bowl heats up quickly since the soup is
in direct contact with the bowl. The top layer of
soup, in contact with air, will cool next. If it’s
a creamy thick soup, the top layer may become a
solid film that you can poke with a spoon. The
film is cool but the soup at the bottom of the
bowl is hotter.
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