YourGemologist
How Rocks are Created!

Billions of years ago......
 ...the earth formed from a huge mass of spinning dust and gas that formed our solar system. After many years the earth cooled enough that it formed a crust on the outer layer. On top of this layer was a vast ocean of water. And on the inside was very hot, molten rocks that were in liquid form. Eventually the pressure inside the earth built up so much that some of the molten rocks came to the surface through fissures in the crust of the earth. These formed what is known as a volcano.

 

 

 ...a big mass of land called a continent. The first continent was one very big land mass called Pangea. This contained all of the land that was on the earth at the time.

 

 

After many millions of years the single big continent began to split apart to make several smaller land masses also called continents. And the process went on until all of the land split apart and drifted moved away from each other, until we have the earth as we see it today as shown below...spinning through space orbiting the sun.


 All of these continents that you see were once joined together. But since they actually move across the face of the earth, the split up to what you see today.

But how did the rocks form during this time? Remember our earth with the volcanoes? Well, these formed big mountains that we can see even today on earth.
Volcanoes formed many mountains
These mountains are made of igneous rocks
Igneous rocks are those formed by cooling magma that pushed its way to the surface of the earth to form the continents. When molten rock is deep inside the earth it is called "magma". When it flows out onto the surface of the earth it is called "lava". In the case of igneous rocks and mountains, the molten rock that came from deep inside the earth pushed to the surface to form the mountains. The mountains are made of igneous rocks.

 

But the rain erodes the mountains away. Eventually, rain will erode the mountains away. Erosion is the process by which rain (or water) and even wind wears down the rocks and turns them into pebbles or sand that washes away down the rivers.

 

The mountains get smaller. Over a long, long time, the mountains start to get smaller and smaller as more and more of their rocks are eroded down to sand and pebbles, and washed down into the sea.

 

 

Mountains become hills.  Eventually the mountains are no longer mountains but only hills...
And eventually they are almost gone.
Below you can see some igneous granite rocks that were once mountains bigger than the Rocky Mountains of the United States. Now they are just big rocks that are about 2 meters high. Can you image these once being higher than the Rocky Mountains?
Igneous rocks that were once mountains
 But what happened to the sand and pebbles that were washed down the river?
As you can see below, the sand and pebbles were washed down the rivers into the sea. There they settle down to the bottom of the sea and are known as sediments.
The mountains get washed into the sea.
 The sediments form layers as you can see in the image above. Eventually these will become so deep that they will become very, very heavy. This weight will also create a lot of heat. The weight and heat will cause the sediments to become rock hard and form a type of rock known as sedimentary rock as you can see below.

 

Notice the layers of sedimentary rock. This was once on the bottom of the sea.
Where ever you see the layers of sedimentary rock as you can see above, you can know that this place was once on the bottom of the sea. It was under water! But after many, many years the bottom of the sea was pushed up and the sea floor with the sedimentary rock became dry land. But there is another aspect to sedimentary rocks.....FOSSILS!
Sedimentary rock layers with fossils...
Sometimes the sedimentary and igneous rocks become pressed really, really hard by other rocks on top of them or forcing their way into the space that the original rocks existed. When this happens all of the rocks become very hot and are put under heavy pressure. This will cause the rocks to change from one type of rock into another. This new type of rock is called metamorphic rock because it changed or morphed into something different. It started out as one type of rock, but due to heat and pressure it changed into another kind of rock. Hence the name: metamorphic!

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