Relative Age The age of a rock unit or event __________ to the age of another rock unit or event. In other words which layer or event came __________, __________, __________… Ex. Mr. Jensen is older than you are or the sandstone was deposited before the fault occurred

Principle of Uniformitarianism What? “The is the Key to the ” What geologists can see going on today are the same that occurred in the past.

________ at the Bottom; ________________ on Top Law of Superposition The Oldest Layers are deposited first (on the bottom) and subsequent layers are deposited on top. ________ at the Bottom; ________________ on Top This assumes there has been no ______________

The rock must be there so it can be _____________ Crustal Deformation All __________, __________, or __________ happened after the layers were deposited The rock must be there so it can be _____________ This includes ___________ _______________ that changes the rock that was “touched” by magma or lava

Absolute Age An actual year or a range of years (sometimes expressed as a __________ __________) Can be determined with ____________ dating Can be determined with the use of ________ __________ and __________ __________ __________

Index Fossils Index fossils (like fads) can help us determine the __________ __________ __________ that the rock formed The best index fossils are those that lived for a relatively _________ period of time and over a __________ area.

Volcanic Time Markers Volcanic ash is sent into the __________ _______________ and is carried all over the Earth __________ of volcanic ash are created all over the Earth. They can be linked to the __________ and __________

                                                                         

Not every Fossil is an Index Fossil Some fossils are not useful for determining the age of a rock because they … Lived for _____ ________ a period of time Too __________ of an area