Rocks.

1. Earth's crust began as molten rock.

2. In the beginning, all rocks were igneous.

3. Volcanoes deliver igneous rocks to the  surface.

4. Rock that forms underground is called intrusive rock.

5. Rock that forms from from igneous rock fragments (sediments) are called sedimentary rocks.
6. Sand that is formed into rock is called sand stone.
7. Layers of coal are formed from remains of living organisms.
8. Limestone is formed from microorganisms' skeletons.
9. Rocks that have been changed since they first formed are called metamorphic rock.
10. Limestone under great pressure turns to marble.
11. When metamorphic rock reaches the surface, it weathers and becomes more sediment.