Fossils and Rock Layers

What is a fossil? Change over time = Evolution! Fossils are the preserved remains or traces of living things Fossils can tell us a lot about the history of our planet! Change over time = Evolution!

How do fossils form? Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. Most fossils are found in sedimentary rock!

Relative Age The relative age of a rock is its age compared to the ages of other rocks. What are some examples?

Absolute Age Absolute age is the number of years since the rock formed. How is absolute age different from relative age?

What is an index fossil? An index fossil is widely distributed and represents a type of organism that existed only briefly. Index fossils can help us determine the age of the rock layer that it is in.

Law of Superposition In horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

Extrusion Lava that hardens on the surface An extrusion is always younger than the rocks below it!

Intrusion Magma cools and hardens into a mass of igneous rock An intrusion is always younger than the rock layers around and beneath it!