32Dynamic planet
Earth’s surface is constantly changing. The rocks it is
made from have been recycled many times. Even
though we rarely feel it moving, the signs that our
planet is active are all around us.
Earth’s metal core provides the heat.
It contains radioactive elements
that give out heat as they become
more stable. Even though the inner
core is very hot, the huge pressure
keeps it solid. The slightly cooler
outer core is liquid.EARTH
RISING HEAT
Below the surface, the mantle moves very slowly.
Scientists think that currents of heat rise from
the lower mantle, cool as they near the surface,
and then sink back down again. This has
a dragging effect on the surface layers,
carrying them along like a conveyor belt.Earth has had a solid outer
skin for at least 4.4 billion years.
Even though the rocks that currently
make up the surface are much younger,
scientists have found that some of them
contain tiny crystals of a mineral called
zircon. Dated at 4.4 billion years,
they are the oldest crystals
known on Earth.^7
/^7
MAGMA erupting
onto the surface cracks
as it cools. The whole
of the planet once
looked like this.