Post on 20-Mar-2018
Relative DatingRelative Dating
I. Relative Dating
• Relative DatingRelative Dating is when you give the age of a rock or fossil comparedcompared to another rock or fossil.
– Example: Rock A is OLDEROLDER than Rock B.– An actual age in years is not determined.
II. Rules of Relative Dating1.1. Law of SuperpositionLaw of Superposition: When sedimentary
rock layers are deposited, younger layers are on top of older deposits.
Rules of Relative Dating2. 2. Law of Original HorizontalityLaw of Original Horizontality: Sedimentary
rock layers are deposited horizontally. If they are tilted, folded, or broken, it happened later.
Rules of Relative Dating3. 3. Law of Cross-Cutting RelationshipsLaw of Cross-Cutting Relationships: If an
igneous intrusion or a fault cuts through existing rocks, the intrusion/fault is YOUNGERYOUNGER than the rock it cuts through
III. III. CorrelationCorrelation• Rock layers in different places and be
correlated or matched upmatched up by matching up the rocks and fossilsrocks and fossils in the layers.
IV. IV. UnconformityUnconformity• When rock has been erodederoded, so you have
a missing sectionmissing section of time in the rock record.
Unconformity
Why are some of the layers tilted?What happened to the top of the folded rocks?The missing rock layers is called an __________.
What type of rocks formed above?
What events might have caused the rock layers to become tilted?Why is the top flat?
What caused the angular unconformity?
Index Fossils• Some species of
organisms only lived for a short period of time before they became extinct. If you use radiometric dating to get an age for the fossil, then you know that the rock the fossil is found in is also that age.
Trilobite: Index fossil for the
Paleozoic EraPaleozoic EraAge: Age: 590-250590-250 mya mya
Graptolite • Index Fossil of the Ordovician PeriodOrdovician Period
• Age: Age: 500-335 500-335 myamya
Fossil B lived 10 million years ago – 2 million years ago.
Fossil A lived 20 million years ago- 8 million years ago.
What do you know about the age of the rock containing both fossils?
• What is “B”? • Place the layers in order from oldest to youngest
Put the events in order
Put the events in order
http://reynolds.asu.edu/glg103/relative_age_principles.htm