Rock Layers

Law of SuperpositionLaw of crosscutting relationshipsLaw of InclusionsFaunal Succession

1. Comparing properties of rock strata

• Color• Texture—sand, silt, or clay

combinations • Composition—look for elements or for

ratios of materials • Fossils—look for fossils of organisms

that only existed for a short period of time

2. Principle of Original Horizontality

• Generally most sediments or lava flows solidify as horizontal layers

• These horizontal layers are called strata. One layer is called stratum.

3. Syncline and Anticline

• Syncline—rock formations that form a downward pointing arch or a trough

• Anticline—upward pointing arch or peak

4. Law of Superposition

• In a sequence of sedimentary rock layers, each layer of rock is older than the layer above it and younger than the rock layer below it

• Can be applied to surface geological events such as lava flows and ash from volcanic eruptions

• Nicolaus Steno (1636-1686) observed the changes in sequence of rock layers while working in the mountains of Italy.

Superposition

5. Faults and Folds

• Faults— cracks in the rock layers where some movement has taken place; produce offset layers

• Folds—bends in the rock layers; They occur after the rock layers formed

Faults

Folds

Folds (cont.)

6. Intrusion

• Sometimes a rock formation will be penetrated by molten rock that forces its way through weakness in the formation.

• The new rock that forms in this way is called an intrusion

• Would this intrusion rock be older or younger than the rock it forms in?

• Younger although it may appear to go through older layers of rock.

Intrusions

7. Law of Crosscutting Relationships

• If a fault or other body of rock cuts through another body of rock, then it must be younger than the rock through which it cuts and displaces

• Originally described by James Hutton (1726-1797)

Crosscutting Relationships

8. Law of Inclusions

• If a rock body (Rock B) contained fragments of another rock (Rock A), it must be younger than the fragments of rock it contained. The intruding rock (Rock A) must have been there first to provide the fragments

• First described by James Hutton

Inclusions—Which rock is older?

9. Law of Faunal Succession

• Fossils of invertebrate (no backbone) animals found in the rock layers appeared in a predictable sequence

• Fossils occur in a definite, invariable sequence in the geologic record

• First described in 1790, by William Smith a British engineer

Faunal Succession

Put the letters in order from oldest to youngest

Plate TectonicsEarth’s interior and exterior

10. Crust • Topmost layer of the earth

11. Mantle

• A layer of rock that is denser than the crust

• Beneath the crust

12. Core

• Center of the earth• Composed of iron and nickel • Inner core—solid metal• Outer core—liquid (molten) metal

Earth’s Interior

13. Lithosphere

• Approximately 60 miles thick

• Made up of the crust and upper portion of the mantle

14. Plate Tectonics

• Many forces change the faces of the earth over time

• The largest force that changes our planet’s surface is movement

• The movement of the outer layer is a process called plate tectonics

Plates of the lithosphere

15. Why do the plates move?—read through then summarize

• Plates at our planet’s surface move because heat in the Earth’s core causes molten rock in the mantle layer to flow.

• We used to think the Earth’s plates just surfed on top of the moving mantle, but now scientists believe that plates help themselves to move.

15. (cont.)• How can plates help themselves move

instead of just surfing along? • Just like convection cells, plates have

warmer, thinner parts that rise, and colder, denser parts that sink.

• New parts of a plate rise because they are warm and thin, pushing the rest of a plate out of its way at spreading ridges .

• Old parts of a plate sink down into the mantle at subduction zones because they are colder and thicker than the warm mantle underneath them.

Movement of plates

Review of Waves

EarthquakesWave types

16. Earthquakes

• Focus—exact point inside earth where an earthquake originates

• Epicenter—point on the surface immediately above the focus

• Waves from the earthquake travel in all directions from the focus and epicenter

17. Longitudinal Wave

• Originate from an earthquake’s focus • Move faster through rock than the

other waves • First to reach recording stations • Travels by compressing the Earth’s

crust in front of it and stretching the crust in back of it

Longitudinal Waves

18. Transverse Waves

• Move more slowly than longitudinal waves

• Called S waves or secondary waves

Transverse Waves

19. Surface Waves

• Moves only across Earth’s surface• Result of Earths’ entire mass shaking

like a bell that has been rung • Rolling action of these waves with

their longer wavelengths can cause buildings to collapse

Earthquake effects

Earthquake Effects

20.Richter Scale • A measure of the

energy released by an earthquake

• Assigns a single number to signify the significance and damage of the earthquake

Richter Scale

Richter Scale