Relative age dating sequence
Taughannock Falls near Trumansburg, New York, illustrating the Principle of Superposition. Superposition is observed not only in rocks, but also in our daily lives. The trash at the bottom was thrown out earlier than the trash that lies above it; the trash at the bottom is therefore older (and likely smellier! Or, think about a stack of old magazines or newspapers that might be sitting in your home or garage: most likely, the newspapers at the bottom of the pile have dates on them that are older than the newspapers at the top of the pile.
The photograph below was captured at Volcano National Park on the Big Island of Hawaii.
Because of cross-cutting relationships, the cut that divides the slice from the rest of the loaf is younger than the loaf itself (the loaf had to exist before it could be cut).
When investigating rocks in the field, geologists commonly observe features such as igneous intrusions or faults that cut through other rocks.
An imaginary cross-section, showing a series of rock layers and geological events (A-I).
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.
Imagine cutting a slice of bread from a whole loaf.Correlation can involve matching an undated rock with a dated one at another location.Suppose you find a fossil at one place that cannot be dated using absolute methods.A curb in Hollister, California that is offset by the San Andreas fault. The cartoon below shows an imaginary sequence of rocks and geological events labeled A-I. This problem could be resolved, however, if we were to observe A cutting across H (i.e., the fault displacing the igneous intrusion).Using the principles of superposition and cross-cutting relationships, can you reconstruct the geological history of this place, at least based upon the information you have available?