World Builders™                                                                            Session Two  --  Geology             

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After many thousands of years your planet will become a world with a solid surface.

     As the cloud of dust particles and frozen gas crystals swirled around your proto-sun, little grains of matter bumped into each other and stuck together.  Gradually the gathering grains became clumps and lumps which grew larger and larger as gravity pulled some of them together. It is hard to imagine entire planets coming together by this process, which is called accretion, and it took a long time.  However, scientists believe that this is how planets and moons come into being.

     Read the science notes about The States of Matter.  You will see that, as matter goes from a gas to a liquid and then to a solid, the electrons,. which help to make up the atoms, have less and less space in which to jump around.   The more matter that there is, the more gravity there is, and eventually the atoms in the middle of the proto-planet get hotter and hotter as they are squeezed closely together.  What happens then?  Well, what happens when you put twenty five people in a phone booth all together?  Right!  The atoms heat up, the electrons struggle, and after a while the whole planet melts into a very hot ball of molten rock.  

     By the way, this is why planets are more or less spherical.  They are already spinning, and gravity is pulling all the atoms toward the center of the ball.  It is during this molten stage that they are smoothed and rounded.  To us the earth seems to have great heights and depths, but, by comparison, its surface is as smooth as the skin on an apple!  Even today, water rushes downhill, carrying mud and gravel to the lower parts of the landscape.  This helps to keep the planet roune!

     Other things happen when a planet becomes molten. The heaviest elements, including much of the iron, are pulled to the center of the molten ball.   Radio-active elements also sink, and contribute to the long term heat in the center of the world.  Lighter elements float to the top, where they later become the continents. As a rocky  planet cools, a crust forms on the outside.  As the rock cools further, cracks develop. Under the crust the rocky material is still very hot, and so somewhat plastic, like very, very thick cookie dough. The plates of rock that crack apart on the surface float on this hot material, and slowly drift apart or collide on the planet's surface.   We will be learning more about these floating tectonic plates.

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