Other Chapters' Lyrics:
Other Chapters' Notes:
Earth Science Chapter 6 - Summary Notes
á Geologists use relative dating to determine whether an object or event is older or younger than other objects or events.
á One way they do this is with the principle of superposition. This states that younger rocks lie above older rocks.
á Scientists use the geologic column, which is an ideal sequence of all dated rock layers, as a standard for dating rocks.
á When rock layers donÕt match the geologic column, it is called unconformity. Missing layers can be caused by erosion, or they were never deposited in the first place.
á Unlike relative dating, absolute dating determines the actual number of years an object has existed. Radiometric dating is the most common method of absolute dating.
á Isotopes are atoms of an element that have different numbers of neutrons. Some are unstable and tend to decay. Radiometric dating calculates age based on the decay of isotopes in an object.
á Evidence of life is preserved in fossils. Fossils form in various ways.
á In permineralization, an organismÕs tissue pores is filled with minerals. Petrified wood is an example.
á Insects sometimes get stuck in tree sap, which then hardens to preserve the insect in amber.
á Some of the best fossils are those of animals frozen so quickly that their bodies never decompose, like the wooly mammoth.
á Fossils tell us what the earth was like in the past. Marine fossils are often found on mountaintops, which means that the rocks were pushed up from sea level in ancient times.
á Index fossils are fossils with known ages. These fossils tell us the age of rock found nearby.
á The geologic time scale divides the EarthÕs 4.6-billion-year history. It is divided into eons, which are divided into eras, then periods, then epochs.