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Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence. The method of reading the order is called stratigraphy (layers of rock are called strata). Relative dating does not provide actual numerical dates/agesfor the rocks. Relative Dating
is the “age” of a rock or strata compared to the ages of other rocks or strata. Relative Age
as sedimentary rocks form, they are deposited on older rock layers. Principle of Superposition
in undisturbed layers, the oldest is on the bottom and higher layers are younger. Principle of Superposition
Principle of Superposition Oldest layer is on bottom (1)
Principle of Superposition The Grand Canyon
Principle of Superposition The Grand Canyon
The law states that layers of sediment were originally deposited horizontally under the action of gravity. Principle of original horizontality
Also known as the principleof faunal succession, is based on the observation that sedimentary rock strata contain fossilized flora (plants) and fauna (animals), and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances. Principle of Fossil Succession.
An igneous/metamorphic rock, fault, or other geologic feature must be younger than any rock across which it cuts.. Principle of Cross- Cutting Relationships
Faults Folds Intrusions Extrusions Unconformities Nonconformities Disconformities Crosscutting Relationships
Flashback: List the principles of Relative dating that apply to the cross section on the right Relative Dating: Flashback
is the idea that the processes occurring on earth today are similar to those that occurred in the past. Uniformitarianism
basically says “The present is the key to the past.” Uniformitarianism
is the idea that geological features formed slowly over long periods of time. Uniformitarianism
claims the Earth is 4.6 billion years old. Uniformitarianism
Sedimentary rocks form in rivers Igneous rocks form faster than sedimentary New rock layers form on top of older ones There are billions of fossils on Earth What does the Principle of Superposition say?
1 2 3 4 They are all the same age Which layer of rock is the oldest?
6000 years 75,000 years 20 million years 4.6 billion years HOW OLD WOULD MOST GEOLOGISTS SAY THE EARTH IS?
Catastrophism Uniformitarianism Geologism Agism According to what theory, is the earth 4.6 billion years old?
are igneous rock layers that form on the surface when lava hardens. Extrusions
are always younger than the layers over which they form. Extrusions
Extrusion Kubu Rock – Botswana, Africa
are igneous rocks that form when magma pushes up into rock layers. Intrusions
are always younger than the rock layers they invade. Intrusions
Intrusion Devil’s Tower, WY
Intrusion Devil’s Tower, WY
Stop and Summarize Stand-up, Hand-up, Pair-up: Create a Venn Diagram with your partner.
In the image below identify as many intrusions and extrusions as you can!
are breaks in the earth’s crust. A fault is always younger than the rock it cuts through. Faults
Faults Shoshone Fault, CA
occur when rock layers are compressed together and bend or curve. Folds
Folds Guadalajara, Spain
Mojave Desert, CA Folds
Stop and Summarize Write-Pair-Share: Create a Venn-Diagram comparing Faults and Folds.
1 Identify the Cross-Cutting Relationships 2 3
SOME Relative Dating Practice Write the correct order of events by numbering their occurrences. Identify the cross-cut relationships in each cross section.
are gaps in the rock sequence (caused by the erosion of rock layers). Unconformities
