Second only to oxygen, silicon is the most abundant element in Earth's crust. It is found in rocks, sand, clays and soils, combined with either oxygen as silicon dioxide, or with oxygen and other elements as silicates.
Gravity is a force that attracts objects. It is also the force that makes objects fall down when you drop them. Because of gravity things on earth have a certain weight. Gravity on Earth pulls objects to the centre of the planet. Every time you throw a ball up into the air it is pulled back to Earth. This occurs in nature all the time.
It does pull the space station downward, just like any other falling object. While gravity is pulling downward, the tendency to move in a straight line would carry it away from Earth. As a result, the space station is always falling but always the same distance from the surface.