Isn’t
it funny to think that the Earth is moving! If we stand perfectly still
and look into the distance, the Earth appears to be perfectly still,
too. But the Earth is actually moving in many different directions. The
Earth rotates around its own axis, and we experience this as day and
night. The Earth is also in motion as it orbits the Sun, and we
experience this movement as the seasons change. We don’t feel the
movement as the Earth spins and rotates, but we know it is happening. There
is another type of movement that affects the Earth. This movement
happens underneath our feet. We don’t usually feel this movement because
it is quite gradual – just a few millimetres every year. With time, the
pressure of this movement builds up, and there is a sudden shift inside
the Earth that we feel as an earthquake. Picture the Earth as if
it were a hardboiled egg. The yolk is the core of Earth and the white
is the mantle. The thin shell around the outside of the egg is like the
thin crust of the Earth. If you bump the egg against a plate, the shell
develops cracks. The Earth’s crust also has cracks. Scientists call
these cracks tectonic plate boundaries. Tectonic plate boundaries The
huge tectonic plates that cover the Earth fit together a bit like
pieces in a global puzzle. The Earth’s mantle under the crust is hot and
flexible so the plates (puzzle pieces) are able to move, but they do so
very, very slowly. There are three different ways the plates move: the
plates can move past each other, they can move apart from each other or
they can move towards each other. Scientists have special names for the way the plates move Transform boundaries
are where the plates meet and try to move past each other. Friction
holds the plates in place, so they cannot simply glide past one another.
Stress builds up and is released as an earthquake. New Zealand’s Alpine
Fault is an example of a transform boundary. Divergent boundaries
are where the plates slide apart from each other, and the space that
this creates is filled with magma and forms new crust. This often
happens below the sea, for example, the Pacific Ocean is growing wider
by about 18 cm per year. Convergent boundaries are where
the plates slide towards each other. Sometimes this creates mountains,
for example, the collision between the Australian plate and the Pacific
plate formed the Southern Alps. When two plates under the ocean collide, they usually create an island as one plate moves beneath the other. The Solomon Islands were created this way. On the move for billions of years Scientists
now think the tectonic plates have been on the move for around 3
billion years, but only 50 or 60 years ago, people thought that the
continents were set in the same position forever. Scientists try to find
out how and why things work. By studying rocks, fossils and
earthquakes, they came up with the new theory of plate tectonics. Nature of science Science
knowledge changes when new evidence is discovered. Scientists first
used fossils and other geological evidence to show that the continents
are on the move. Today, they use GPS to track tectonic plate movement.
