Download Plate Tectonics

Plate Tectonics
The Dynamic Earth
The Dynamic Earth
• The Earth both inside and out is dynamic
(always changing).
Studying the Earth’s layers
• Scientists, called geologist, study the Earth’s
rock layers to determine the age of the rocks
and to understand the layers of the planet
beneath our feet.
Layers
• The order of the rock layers determines their
age.
• The oldest rock layers are on the bottom.
• The newer layers are on the top of the older
layers as long as the layers have not been
disturbed.
• When forces disturb the layers, they are no
longer neatly stacked so it is harder to date
the layers.
Events that disturb the rock layers
• Faulting: a break in the Earth’s crust along
which blocks of crust slide against each other.
Events that disturb the rock layers
• Intrusion: molten rock from the Earth’s
interior that squeezes into existing rock and
cools.
Events that disturb the rock layers
• Folding: happens when rock layers bend and
buckle from Earth’s internal forces.
Events that disturb the rock layers
• Tilting: happens when rock layers slant
without folding.
Label the layers (oldest layer=#1)
•
•
•
•
•
•
A. 6
B. 5
C. 3
D. 2
E. 1
F. 4
A
B
F
D
E
C
Geologic Change
• Most geologic change, such as the formation
of mountains, canyons and oceans occurs
gradually.
• For example: Mt. McKinley in Denali National
Park in Alaska “grows” 1 inch per year.
The Grand Canyon
• The Grand Canyon is one of the best places to see
Earth’s history recorded in rock layers. The walls are
made from sedimentary rock.
• The oldest layers are 2 billion years old, which is
almost ½ as old as the Earth.
• The Earth is about 4.5 billion years old!!!
Sudden changes
• Not all geologic changes occur gradually, however. There have
been some catastrophic, or “sudden” changes in history of the
Earth that have caused rapid extinction of some species.
• For example: asteroids and comets have struck the Earth
creating large craters.
• An Asteroid impact may have led to the extinction of
dinosaurs.
Continental Drift
• The continental drift hypothesis—continents
have moved slowly to their current locations.
Continental Drift
1. All continents were once connected as one
large landmass now called Pangea.
Pangea
• The land mass broke apart, and the continents
drifted to their present positions.
Evidence of Continental Drift
a. Puzzle-like fit of the continents
b. Similar fossils have been found on different
continents.
Evidence of Continental Drift
c. Remains of warm-weather plants in Artic
areas and glacial deposits in tropical areas
suggest that continents have moved.
Evidence of Continental Drift
d. Similar rock structures are found on different
continents.
Africa
South America
• At first, continental drift was not accepted
because no one could explain how or why
continents had moved.
Evidence of Continental Drift
Seafloor Spreading
• Using sound waves, scientist discovered a
system of underwater mountain ranges called
the mid-ocean ridges in many oceans.
Theory of seafloor spreading
• In the 1960s, Harry Hess suggested the theory
of seafloor spreading to explain the ridges.
Seafloor Spreading
1. Hot, less dense material below Earth’s crust
rises upward to the surface at the mid-ocean
ridges.
Seafloor Spreading
2. Then, it flows sideways, carrying the seafloor
away from the ridge.
Seafloor Spreading
3. As the seafloor spreads apart, magma moves
up and flows from the cracks, cools, and forms
new seafloor.
Evidence of seafloor spreading
• Youngest rocks are located at mid-ocean ridges.
• Reversals of Earth’s magnetic field are recorded by
rocks in strips parallel to ridges.
Seafloor spreading
C
A
D
B
• C. Molten rock flows onto the seafloor and hardens as it cools
• A. Hot, molten rock is forced upward toward the seafloor at a mid-ocean
ridge.
• D. New seafloor moves away from the ridge, cools, becomes denser, and
sinks.
• B. Molten rock pushes sideways in both directions as it rises, moving the
mantle with it.
Theory of Plate Tectonics
Plate Movements
1. Earth’s crust and upper mantle are broken
into sections.
2. The sections, called plates, move on a plasticlike layer of the mantle.
Plate Movements
3. The plates and upper mantle form the
lithosphere.
4. The plastic-like layer below the lithosphere is
called the asthenosphere.
Lithosphere
Asthenosphere
Plate Boundaries
Plate boundaries
1. Plates moving apart—divergent boundaries.
Plate boundaries
2. Plates moving together – convergent boundaries.
a. Denser plates sink under less dense plates
(subduction zones).
b. Newly formed hot magma forced upward forms
volcanic mountains.
Plates Collide
• Plates crumple up to form mountain ranges.
• Earthquakes are common.
Transform Boundaries
• When plates slide past one another, they are
called transform boundaries.
• Sudden movements can cause earthquakes.
• This is an example of what happened in Haiti.
Convection currents in the Earth
• Convection inside the Earth is the cycle of
heating, rising, cooling, and sinking of material
inside the Earth.
• This is thought to be the force behind plate
tectonics.
Features caused by plate tectonics
1. Faults and rift valleys
Features caused by plate tectonics
2. Mountains and volcanoes
Features caused by plate tectonics
3. Strike-slip faults are the cause of earthquakes.
Testing for plate tectonics
• Scientists can measure movements as little as
1 cm per year.