Presentation on theme: "Dating Rock Layers. Relative vs. Absolute Age Relative Age? What is Relative Age? – The age of an object or event in comparison to another object or event."— Presentation transcript:
Dating Rock Layers
Relative vs. Absolute Age Relative Age? What is Relative Age? – The age of an object or event in comparison to another object or event. Absolute Age? What is Absolute Age? – The actual age, in years, of a rock or fossil. Tells how many years ago a rock or fossil was formed.
Relative Age Methods of determining Relative Age: 1.Law of Superposition 2.Extrusion & Intrusion 3.Faults 4.Unconformities
What is the Law of Superposition? Law of Superposition- The Law of Superposition- in undisturbed SEDIMENTARY rock layers, the older layers are at the bottom and younger layers are above it.
What is Extrusion? ExtrusionExtrusion is when magma cools on the surface of the earth. –Forms a YOUNGER layer than the rock below.
Here’s an Extrusion
What is Intrusion? Intrusion Intrusion is when magma is forced into older rock layers and cools. – Forms a YOUNGER layer within the layers of rock.
Here’s an Intrusion
Extrusions? Intrusions? First of all, which rock layer is the oldest?What is this called? INTRUSION EXTRUSION F G C D A B E More rock layers are deposited on top of the extrusion.
What is a Fault? FaultsFaults are a BREAK in the Earth’s crust due to tectonic plates colliding and rock layers being squeezed together. –Faults are YOUNGER than the rock they cut through. –Faults move over time, which causes rock layers to move. This makes it difficult to determine the age or the surrounding rock.
Faults This crack in the rock layers is called a fault. Faults move over time causing the rock layers to move.
Faults As more time goes by, more rock layers are added on top. Making aging the rock layers difficult.
Faults A A B B C C D E Geologists must then label each of the rock layers. This can be tough because they weren’t around to see the whole process occur.
What is Unconformity Unconformity Unconformity is when new rock layers meet a much older rock surface beneath. – Shows where some rock layers have been lost due to erosion.