GEOLOGIC PRINCIPLES RelativeAge Dating Relativeage dating helps scientists

GEOLOGIC PRINCIPLES

Relative-Age Dating � Relative-age dating helps scientists place geologic events in order. They use certain principles to help them do this correctly.

Principle Of Superposition � In a sequence of undeformed sedimentary rocks, the oldest beds are on the bottom and the youngest are on the top. Youngest Oldest

Principle Of Original Horizontality � Sedimentary layers are horizontal, or nearly so, when originally deposited. Layers that are not horizontal have been deformed by movements of the Earth’s crust.

Principle Of Faunal Succession � � Groups of fossil plants and animals occur in the geologic record in a definite and determinable order. A period of geologic time can be recognized by its respective fossils.

Principle of Crosscutting Relations � Geologic features, such as faults, and igneous intrusions are younger than the rocks they cut.

Principle of Inclusion � A rock body that contains inclusions of preexisting rocks is younger than the rocks from which the inclusions came from.

Folds � � � If rocks are folded, the folding is younger than the youngest rock affected. If they are folded into a syncline a U-shape fold, the youngest rocks are in the core of the fold. The youngest rocks are on the top of the dome if it is an anticline.

Faults � � A fault is a break in the earth’s crust along which movement has occurred. Faults tell us about Earth’s history. The layers affected are older than the shift of the fault line.

Intrusions & Metamorphism � � Intrusions can cause contact metamorphism. The intrusion and metamorphism are younger than the surrounding rock.

In Conclusion � Relative-age dating can be tricky but if geologic principles are used and one breaks the story into pieces it can be nothing short of fun!