Rock Layers Geologic Time MS-ESS1-4

Absolute dating

Any method of measuring the age of an object, like tree rings or carbon dating, is called absolute dating. Absolute dating is when scientists figure out exactly how old something is by using specific methods like analyzing tree rings or measuring radioactive decay.

Eon

The largest unit of the geologic time scale, it is divided into eras, periods, and epochs. Eon is the longest time frame in Earth's history where big changes happen, like the formation of continents.

Era

The second-longest unit of geologic time, it is divided into periods. An era is a large span of time in Earth's history marked by major events or changes.

Fossil record

The history of life recorded by all the fossils we have collected. Fossil record. The fossil record is like a history book made of fossils that shows us how life on Earth has changed over millions of years.

Geologic time scale

A timeline of Earth's history based on major changes. Geologic time scale. The geologic time scale is a way to understand Earth's history by dividing it into different time periods based on significant events and changes.

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 is a tool scientists use to figure out how old other rocks and fossils are by comparing them.

Law of superposition

The oldest rock layers are at the bottom and youngest are at the top. Law of Superposition. In geology, the law of superposition means that in any sequence of undeformed sedimentary rocks, the layers on the bottom are older than the layers on top.

Radiometric dating

Comparing the amount of radioactive and nonradioactive isotopes to determine rock age. Radiometric dating. Its a science method used to find out how old rocks or fossils are by measuring the decay of tiny particles inside them.

Relative dating

A method of comparing fossils or rocks to determine which is older relative dating. Relative dating is figuring out the age of rocks or fossils by looking at their positions in layers of Earth.