Relative Dating

I. Relative Dating Relative Dating is when you give the age of a rock or fossil compared to another rock or fossil. Example: Rock A is OLDER than Rock B. An actual age in years is not determined.

II. Rules of Relative Dating Law of Superposition: When sedimentary rock layers are deposited, younger layers are on top of older deposits.

Rules of Relative Dating 2. Law of Original Horizontality: Sedimentary rock layers are deposited horizontally. If they are tilted, folded, or broken, it happened later.

Rules of Relative Dating 3. Law of Cross-Cutting Relationships: If an igneous intrusion or a fault cuts through existing rocks, the intrusion/fault is YOUNGER than the rock it cuts through

III. Correlation Rock layers in different places are linked or matched up by the rocks and fossils in the layers.

IV. Unconformity When rock has been eroded, so you have a missing section of time in the rock record.

Why are some of the layers tilted Why are some of the layers tilted? What happened to the top of the folded rocks? The missing rock layers is called an _unconformity.

Index Fossils Some species of organisms only lived for a short period of time before they became extinct. Fossils are the preserved physical remains of deceased organisms that are at least 10,000 years old NOTE: Most organisms DO NOT become fossils after death NOTE: The formation of fossils is a RARE event Trilobite: Index fossil for the Paleozoic Era Age: 590-250 mya

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. We can tell if one fossil is older than another based on which layer we find it in. (Deeper layers-older. Shallow layers-younger)

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