Which two of the following sentences from the article include central ideas of the article?

Over long periods of time – millions and millions of years – all rocks play a part in Earth's recycling system.
Magma that intrudes or pushes itself into layers and cracks of existing rocks underground forms intrusive igneous rocks, like granite.
The only parts of the rock cycle that we can easily observe are the surface processes that break down rocks, called erosion, and that build up rocks, called deposition.
There are many types of landslides, but they all involve large amounts of moving rocks.