Earth Science
Earth History
Principles of Relative Dating
Study Tip
Archaeologists use relative dating much the same way a crime scene investigator may look at clues at a scene to find out when a crime occurred.
Relative Age Dating
- Used to determine the ages of materials relative to each other.
- With evidence, archeologists can determine whether one rock is older than another and when a process occurred relative to those rocks.
Study Tip
Archaeologists use relative dating much the same way a crime scene investigator may look at clues at a scene to find out when a crime occurred.
Steno’s Laws
- Steno’s Laws
- Original Horizontality:
- Sediments are deposited in fairly flat, horizontal layers.
- If a sedimentary rock is found tilted, the layer was tilted after it was formed.
- Lateral Continuity:
- Sediments are deposited in continuous sheets that span the body of water that they are deposited in.
- When a valley cuts through sedimentary layers, it is assumed that the rocks on either side of the valley were originally continuous.
(a)Original horizontality (b) Lateral continuity (c) Superposition
- Superposition:
- Sedimentary rocks are deposited one on top of another.
- The youngest layers are found at the top, and the oldest layers towards the bottom.
More Principles of Relative Dating
- William Smith (1769-1839)
- Principle of Faunal Succession
- Some fossil types are never found with certain other fossil types. For instance, human ancestors are never found with dinosaurs.
- Fossils in a rock layer represent what had lived during the period the rock was deposited.
- James Hutton (1726-1797)
- Cross-Cutting Relationships
- Younger rocks crosscut older rocks, and this relationship helps geologists determine the relative age of the rocks.
In this image, A must have existed first for B to crosscut it.
