Convection Currents Inside the Earth, the source of the heat is the extremely hot core. This heat from the interior rises toward the surface of the Earth. It causes liquid rock in the mantle to move with it. Hot and less dense liquid rock moves upward. Cool heavy rock sinks downward. This circular movement of matter is known as convection . Convection occurs within the liquid rock of the lithosphere’s mantle. http:// education.sdsc.edu/optiputer/flash/convection.htm
Scientists believe that convection in the mantle is the reason why the crustal plates move. The plates ‘ride’ on convection currents. The plate motions, of course, result in volcanoes, earthquakes and mountain building. Convection caused Pangaea to break up. The convection currents pushed the continents to where they are today.
Plate movements have led to continental drift. 225 million years ago all the land masses were fused to form a super-continent - Pangea. 200 million years ago Pangea began to move apart to form two great land masses - Laurasia and Gondwanaland. About 135 million years ago it was possible to make out land masses that looked more like those we see today. For example it is possible to see how South America and Africa were drifting apart to form separate continents.
Pangea has now separated to form the continents we know today. The continents are made of “continental crust” and the oceans rest on “oceanic crust”. But what are the thick black lines?
Direct Evidence that the Earth is structured in layers
This is evidence that can be seen on the Earth’s surface
For instance rock samples
Another example is volcanic evidence, such as volcanic gases and volcanic materials