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Dating Rocks Ways to tell the age of a rock. 2 Ways to Date Rocks: Relative Dating: Places events in geologic history in the proper order. The basis for.

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Presentation on theme: "Dating Rocks Ways to tell the age of a rock. 2 Ways to Date Rocks: Relative Dating: Places events in geologic history in the proper order. The basis for."— Presentation transcript:

1 Dating Rocks Ways to tell the age of a rock

2 2 Ways to Date Rocks: Relative Dating: Places events in geologic history in the proper order. The basis for the geologic time scale Mainly Sedimentary Rocks Does not provide a true age Relative Dating: Places events in geologic history in the proper order. The basis for the geologic time scale Mainly Sedimentary Rocks Does not provide a true age

3 2 Ways to Date Rocks: Absolute Dating: All you need is a tiny sample of material (mineral, bone) no larger than a grain of rice. Gives us the true age of a fossil or rock Mainly organic tissue or igneous crystals Measure the amount of unstable isotopes that have decayed to figure out age Absolute Dating: All you need is a tiny sample of material (mineral, bone) no larger than a grain of rice. Gives us the true age of a fossil or rock Mainly organic tissue or igneous crystals Measure the amount of unstable isotopes that have decayed to figure out age

4 Principles for Relative Dating: Superposition - The youngest rocks are on the top, oldest at the bottom.

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6 Relative Dating Principles Superposition Cross-cutting relationships - Geologic features that cut through and across rocks are younger than those rocks. Mostly Faults and Igneous intrusions

7 Cross-cutting Igneous Rock Cross Cutting Relationships - Geologic features that cut through and across rocks are younger than those rocks.

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9 Relative Dating Principles Superposition Cross-cutting relationships Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in.

10 Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in.

11 Relative Dating Principles Superposition Cross-cutting relationships Law of Inclusions Law of Original Horizontality (and Lateral continuity) – layers of sediments are originally deposited horizontally

12 Hikingtripsreport.com

13 Relative Dating Principles Superposition Cross-cutting relationships Law of Inclusions Law of Original Horizontality (and Lateral continuity) Law of Unconformities

14 A DISCONFORMITY is a boundary between two layers of non-continuous ages. This boundary is usually marked by an erosional surface and is often irregular. M&W4 Fig. 17.8; M&W5 Fig. 17.8

15 An ANGULAR UNCONFORMITY is a disconformity between layers of different angles. The underlying layers are first tilted, then erosion scours away a new, horizontal surface. New, horizontal layers form on top

16 An NONCONFORMITY is a disconformity between different rock types, one of them sedimentary.

17 Activity 2: Label the layers from: A The Oldest T The Youngest

18 Activity 2: Label the layers from: A The Oldest T The Youngest


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