Download The earths crust is not a complete “skin”. It is actually “broken” into

The earths crust is not a complete “skin”. It is
actually “broken” into many large pieces called
tectonic plates. The table overleaf outlines all the
important things you need to know about tectonic
plates.
Fact about plates
Reason
They move
Heat given off by the core because of
radioactive decay of uranium causes
convection currents in the mantle.
(remember the mantle can flow like a
liquid) – see beginning of this booklet
for info on convection currents.
Volcanoes occur at the
boundaries between
One plate boundary can be pushed
underneath another causing it to
turn to magma. This magma gets
released under high pressure in an
eruption.
Earthquakes occur at
plate boundaries
Plates rub against each other as they
move. Sometimes they get a little
stuck. Over time enough pressure
builds up, causing the plates to snap
free from each other. This sudden
movement is an earthquake.
Very hot
Earth.
People used to think (wrongly) that
mountains on earth have formed
because the earth shrank as it cooled
after the big bang. They believed
that this shrinking caused the crust to
wrinkle – giving us all our hills and
mountains.
Thanks to a man named Alfred
Wegener, we now know this is not the
case. Wegener showed us mountains
were created by tectonic plates
pushing up against each other
Wegener believed that all the land on Earth had originally been one
giant country called Pangaea, and that over time movement of plates had
created our continents as we know them today……….
Pangaea
Earth as we know it
People ridiculed Wegener. After all, nobody
could see the plates moving, they travel so
slowly (a couple of cm per year).
It was a long time before his ideas were
respected, and it was three pieces of evidence
that won the crowd over for him!!
1. The Jig-Saw Fit..
Look in your textbooks and see how the shapes of
Africa and South America seem to fit together like
pieces of a jigsaw. Wegener noticed this fit in
other continents. This indicates they may have
been joined at one point!
2. Fossil Evidence…
We don’t have fossils of Kangaroos in this country
because they don’t live here. They evolved in
Australia and they are stuck there. However,
fossils of the same animals are found in Africa and
South America – this would clearly not be possible
unless the two continents used to be joined. (that
is unless prehistoric animals operated their own
airline!!!)
3.Rock types……
It was also noticed that the types of rock on the
east coast of South America and the west Coast of
Africa were identical, even down to the way they
had been folded over the years. This is another
extremely strong indicator that both land masses
used to be joined together.