Rocks and Fossils
Rocks are grouped into three types based on how they form: igneous, sedimentary, and metamorphic.
The three rock types
Igneous rocks form when melted rock (magma) cools and hardens. Sedimentary rocks form when layers of sediment are squashed together over millions of years. Metamorphic rocks form when existing rocks are changed by intense heat and pressure.
How fossils form
Fossils are usually found in sedimentary rock. When an animal or plant dies and gets buried in sediment, its hard parts (like bones or shells) can be preserved and slowly turn to rock over millions of years.
Practice
Why are fossils mostly found in sedimentary rock rather than igneous rock?