Rocks and rolls
Sedimentary: Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water.
Metamorphic: Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (1500 bars), causing profound physical and/or chemical change.
Igneous: Igneous rock is formed through the cooling and solidification of magma or lava.
Metamorphic: Slate is a grained metamorphic rock.
Igneous: Obsidean is made by molten lava then cooled later to have a black/dark brown look.
Sedimentary: Brecci is made up of angular pebbles cemented together.
Stratification: Stratification is the dividing of people or things into different groups or layers.
Scientists combine several well-tested techniques to find out the ages of fossils. The most important are Relative Dating, in which fossils and layers of rock are placed in order from older to younger, and Radiometric Dating, which allows the actual ages of certain types of rock to be calculated. The different layers of the rocks tell how old it is.
Because over time more and more layers are added to the sedimentary rock and builds and up which is why the rock higher up is usually younger.
They die and their skeletons/shells build up layers. They dig holes in the ground allowing water to run into the ground. They build dams creating lakes. The eat vegetation promoting erosion. They send roots into cracks that can break down mountains.