Rock Layers
Law of Superposition
Law of crosscutting relationships
Law of Inclusions
Faunal 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 Tectonics
Earth’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
Earthquakes
Wave 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