The Fossil Record MS-LS4-1

Fossil record

The history of life recorded by all the fossils we have collected. Fossil record. The fossil record is the collection of all known fossils and their placement in rock layers, which helps us understand how life on Earth has changed over time.

Geologic time scale

A timeline of Earth's history based on major changes. Geologic time scale. The geologic time scale is a system used to organize Earth's long history into different periods based on major events or changes, like the appearance or disappearance of certain types of life.

Homologous structure

A similar structure in different species, like a whale fin, bat wing, and your arm, is a homologous structure. Homologous structures are body parts that are similar in different species because they were inherited from a common ancestor.

Index fossil

A fossil from an organism that existed for a short time, it is used to determine the age of other fossils. Index fossil. An index fossil helps scientists figure out how old other fossils are by comparing layers of rock.

Law of superposition

The oldest rock layers are at the bottom and youngest are at the top. Law of superposition. This law helps us understand that in undisturbed rock layers, the bottom layers are older than the ones above them.

Radiometric dating

Comparing the amount of radioactive and nonradioactive isotopes to determine rock age. Radiometric dating. It is a method used to find out how old rocks are by measuring the decay of radioactive elements.

Uniformitarianism

The theory that geologic processes are the same today as they were in the past. Uniformitarianism. It means that Earth's processes, like erosion and sedimentation, have worked the same way throughout history.