This document discusses principles of relative dating used to determine the sequence of geological events and the age of rock layers. It describes three key rules: 1) the law of superposition stating that younger layers are above older layers, 2) uniformitarianism stating that geological processes today are the same as in the past, and 3) cross-cutting relationships showing intrusions and faults occurred after existing rock layers. It also defines three types of unconformities - angular, disconformity, and nonconformity - which indicate gaps in the geologic record due to erosion.

1. Relative Dating Chapter 13 Clues to Earth’s Past

2. Rules of Relative Dating Law of Superposition – the youngest layers are on the top and oldest on the bottom. Layers are always laid down flat. Uniformitarianism – processes happened in the past just as they happen today. Volcanic eruptions Erosion Fault movement Look out for unconformities !!! *layers that are missing from erosion

3. Cross-cutting Relationships Intrusions –magma comes up into faults or between layers ( the layers were there 1 st ) Faults crack the layers after they have formed ( the sidewalk is there before the crack ) Folding of rock layers happens after they have been laid down flat.

4. 3 types of unconformities Like pages missing from the middle of a book Erosion takes away layers leaving a gap in the rock record. Correlation of rock sequences – by comparing rock layers from different areas a complete record of layers can be determined. 3 types Angular unconformity Disconformity Nonconformity

5. Angular unconformities Horizontal sedimentary layers are TILTED when they are uplifted then eroded. New sedimentary layers are deposited on top of this erosional surface. Look for angles in the lower rock layers!

6. Disconformity Sedimentary rock layers were uplifted and eroded. New sedimentary layers were added on top of this erosional surface. The layers are ALL parallel. There is a gap in the rock record.

7. Nonconformity Igneous or metamorphic rocks are uplifted and eroded Sedimentary rocks are deposited on top of this erosion surface The surface between the 2 different rock types is a nonconformity.

8. Which came first?

9. Answer key 1 2 3 6 4 8 9 11 12 7 5 10 13 erosion 6 intrusion 7 unconformity 10 fault