1. Relative Dating

3. Relative Dating
Relative Age: the age of something compared to something else.
Absolute Age: the actual age of a rock or an event
Relative age = older, younger, etc.
Absolute age = in years

4. The Principal of Superposition
In undisturbed sedimentary rock layers (strata), the oldest rock is at the bottom.
YOUNGEST rock layer
Exceptions: deformed rock layers (folded layers, faults, etc.) – draw pictures
OLDEST rock layer

5. Dating Intrusions, Extrusions, & Inclusions
Intrusion: when magma squeezes into preexisting rocks and cools.
YOUNGER than any rock it cuts through
Intrusion = cm to 100s of kilometers

6. Dating Intrusions, Extrusions, & Inclusions
Extrusion: when lava flows on the SURFACE and cools.
YOUNGER than rocks beneath it
OLDER than rocks above it.
Lava flows, volcanoes,

7. Dating Intrusions, Extrusions, & Inclusions
Inclusion: a piece of older rock within igneous rock.
Magma rises to surface – pieces of rock that it is intruding into can break off and fall into magma. If magma is cool enough, rock will not melt, and stay a part of the magma.

8. Cross-Cutting Relationships
Types of Cross-cutting relationships: Intrusions, faults, veins, etc.
These features are YOUNGER than the rocks they cut across.

9. Cross-Cutting Relationships
A fault is younger than the rock layers it cuts across
An igneous intrusion is younger than the rock
it penetrates

10. Dating Rock Features
The folding and tilting of rock layers are events that are younger than the rock layers they effect.

11. Unconformity – A surface of erosion between rock layers that represents a missing gap in Earth’s history.
Uplifting and folding
Deposition
Unconformity
Subsidence
Erosion

12. Correlation
The process of showing that rock layers, or geologic events, from different places are the same, or similar in age.
Types of Correlation:
Exposed bedrock
Similarities in Rocks
Use of Index Fossils
Volcanic Ash or Meteorite Deposits
Helps to determine the sequence of geologic events in an area.
Helps to find certain mineral resources, such as fossil fuels, bc they’re only found in rocks of specific age.

14. 1. Correlation by Exposed Bedrock
Bedrock is usually covered with soil, but can occasionally be exposed.
Correlation can be accomplished by directly following the rock layers.
River valley, road cut, etc.
OUTCROPS – exposed layers of bedrock

15. 2. Correlation by Similarities in Rocks
Rocks can be correlated by having similar appearance, color, mineral composition, and rock sequence.
Only valid in small areas
May be incorrect – similar rocks can form in similar envt millions of years apart.

16. 3. Correlation by Index Fossils
Index Fossil: a fossil that is used to date the rock layers in which it is found.
An organism that lived during a relatively short, well-defined time span.
Have a wide distribution geographically.

17. Which of these is an INDEX FOSSIL?

18. 4. Correlation by Volcanic Ash and Meteorite Deposits
Volcanic Ash: ash from each volcanic eruption has unique composition
Ash deposits are widely distributed, and represent a small period of time.
Meteorite Deposits: rock particles and debris produced by an asteroid, comet, or meteorite impact can cover large areas of Earth.
Specific ash deposits can be detected in rock layers.
Specific age markers in rocks and glacial ice 1000s of km apart.
EX: 65mya, meteorite hit Yucatan Peninsula in Mexico – Debris can be found in ALL of earth’s continents

19. “SEQUENCE OF EVENTS” PRACTICE WORKSHEETS

20. Sequence 1: Uplift & Erosion
Limestone deposited
Sandstone deposited
Shale Deposited
Uplift
Erosion

21. Sequence 2: Faulting Limestone deposited Sandstone deposited
Shale deposited
Faulting

22. Sequence 3: Folding Limestone deposited Sandstone deposited
Shale deposited
Folding

23. 6 5 7 4
6(erosion) 4 4
Folding
5(tilting) 3 3 3 2 2 2 1 1 1
Oldest- Shale
Youngest- Folding
Oldest- Shale
Youngest- Siltstone
Oldest- Sandstone
Youngest- Shale
Oldest- Limestone
Youngest- Igneous Intrusion
Oldest- Sandstone
Youngest- Igneous Intrusion
Oldest- Shale
Youngest- Fault 4 4 4 6 3 3 5 3 2 2 2 5 6 5 1 1 12 1

24. 5 4 6 3 2 7 1 Oldest- Siltstone Youngest- Igneous Intrusion link
unconformity formation 13