Transcript Chapter Four – Earth Science

Chapter Four – Earth Science
Plate Tectonics
Section 4-1-Earth’s Interior
• Three main layers:
– The Crust
– The Mantle
– The Core: inner core/outer core.
Earth’s Layers
The Crust
The Crust: the layer of rock that forms Earth’s
outer skin. In includes both dry land and the
ocean floor. The crust beneath the ocean is the
oceanic crust – made mostly of basalt. The
crust that forms the continents, called
continental crust, is made mostly of granite.
The Mantle
• Below the crust is the Mantle. This is a hot
layer of rock. The crust and the uppermost
part of the mantle together form the
lithosphere. Beneath the lithosphere is a
softer layer called the asthenosphere.
The Core
• Earth’s core consists of two parts:
– The outer core is made of metals iron and
nickel. The outer core is a layer of molten
metal that surround the inner core.
– The inner core is also made of iron and nickel.
The inner core is a dense ball of of solid metal.
– The movement of both the inner/outer core
creates Earth’s magnetic field, which causes the
planet to act like a giant bar magnet.
Convection Currents
• The movement of energy from a warmer
object to a cooler object is call heat transfer.
There are three types of heat transfer:
– Radiation
– Conduction
– Convection
Radiation
• The transfer of energy through empty space.
Heat transfer by radiation takes place with
no direct contact between a heat source and
an object.
– Example: Sunlight warms the Earth’s Surface
Conduction
• Heat transferred by direct contact of
particles of matter. In conduction, the
heated particles of a substance transfer heat
to other particles through direct contact.
– Example: Use a spoon to eat soup. The hot
liquid transfers heat to the spoon and the spoon
becomes hot.
– Example: Stirring coffee with the spoon.
Convection
• The transfer of heat by the movement of a heated liquid.
Fluids include liquids and gases. During convection,
heated particles of a fluid begin to flow, transferring heat
energy from on part of the fluid to another.
– Example: Hot Tub
– Example: Heating a pot of soup. As the soup on the
bottom gets hot, it expands and becomes less dense.
The warm, less dense soup moves upward, floating
over cooler, denser soap. Then gravity pulls this cooler,
denser soup down to the bottom and the process
continues.
Convection Currents
• The process of the heating and cooling of fluid, changes in
the fluids density, and the force of gravity that combine
and cause this flow is a convection current.
• Convection Currents flow in the asthenosphere. The heat
source for these currents is heat from Earth’s core and from
the mantle itself. Hot columns of mantle material rise
slowly. At the top of the asthenosphere, the hot material
spreads out and pushes cooler material out of the way. The
cooler material sinks back into the asthenosphere.
Convection Currents
• Convection Currents: large convection systems
in the mantle may carry along the plates of the
lithosphere like a conveyor belt.
Section 4-3 – Drifting Continents
• Alfred Wegener wondered why the coasts of
several continents matched so well.
– Wegener’s hypothesis was that all the continents had
once been joined together in a single landmass and have
since drifted apart. The Super-continent was named
Pangaea – “all lands”.
– Pangaea existed 300 million years ago, and over tens of
millions of years, Pangaea broke apart and drifted to
their present-day locations, becoming the seven
continents today: North America, South America,
Africa, Australia, Antarctica, Europe, and Asia.
Alfred Wegener
Pangaea
Continental Drift
Continental Drift
• Simulation of moving plates:
http://www.enchantedlearning.com/subjects/as
tronomy/planets/earth/Continents.shtml
The Continental Drift
•
The idea that the continents slowly moved over
Earth’s Surface became known as the
continental drift. Wegener presented evidence to
support his theory:
1. Mountain Ranges and landforms provide
evidence for continental drift. Mountain ranges
in South America and Africa line up. Also,
European coal fields match with similar coal
fields in North America. We know coal is a
product of once living, animals and plants.
Evidence
2.
3.
Evidence from Fossils: Fossils of the plant Glossopteris
has been found in rocks on widely separated landmasses.
Additionally, fossils of the reptiles Mesosaurus and
Lystrosaurus also have been found on widely separated
landmasses.
Evidence from the Climate: An island in e Artic Ocean
contains fossils of tropical plants. The island at one time
must have been close to the equator. Also, scratches in
rocks made by glaciers have been found in South Africa.
Wegener stated Earth’s climate has not changes, but the
positions of the continents have changed.
Continental Drift
• Wegener could not provide a satisfactory
explanation for the force that pushes or
pulls the continents. Most geologists
rejected his theory. Due to new evidence,
Wegener’s theory is being reconsidered.
4-4 Sea Floor Spreading
• Scientists mapped the mid-ocean ridge
using sonar.
– Mid-Ocean ridge is the longest chain of
mountains in the world, curving along the sea
floor of all Earth’s oceans.
– Sonar is a device that bounces sound waves off
underwater objects and then records echoes of
these sound waves.
4-4 Sea Floor Spreading
Earth’s ocean floors move like a conveyor belt,
carrying the continents with them. This
movement begins at the mid-ocean ridge.
The ridge forms along a crack in the oceanic
crust. At the mid-ocean ridge, molten material
rises from the mantle and erupts. The molten
material then spreads out, pushing older rock to
both sides of the ridge.
4-4 Sea Floor Spreading
• Then more molten material splits apart the
strip of rock, pushing it aside. This process,
called sea-floor spreading, continually adds
new material to the ocean floor.
Sea-floor spreading
4-4 Evidence
1.
2.
3.
Scientists have found strange rocks shaped like pillows
in the central valley of the mid-ocean ridge. Such rocks
can form only if molten material hardens quickly after
erupting under water.
Scientists discovered that the rock that makes up the
ocean floor lies in a pattern of magnetized strips.
Lastly, the last piece of evidence came from rock
samples, the farther from the ridge the rocks were taken,
the older they were.
Evidence – Further Reading
http://kids.earth.nasa.gov/archive/pangaea/evi
dence.html
4-4 – Sea Floor Spreading
• The ocean floor does not just keep spreading, it
also sinks beneath deep underwater canyons called
deep-ocean trenches.
• Where there are trenches, subduction takes place.
Subduction is the process by which the ocean floor
sinks beneath a deep-ocean trench and back into
the mantle. This happens over tens of millions of
years.
4-4
• The process of subduction and sea-floor
spreading can change the size and shape of
the oceans. Because of these processes, the
ocean floor is renewed about every 200
million years.
– The Pacific Ocean is shrinking.
– The Atlantic Ocean is expanding.
4-5 Theory of Plate Tectonics
• Earth’s lithosphere is broken into separate
sections called plates. The plates fit closely
together along cracks in the crust.
The Theory of Plate Tectonics
The Theory of Plate Tectonics
• Plate Tectonics is the geological theory that
states pieces of the Earth’s lithosphere are in
constant, slow motion, driven by convection
currents in the mantle. The theory of plate
tectonics explains the formation, movement,
and subduction of Earth’s plates.
Divergent Boundary
• Two plates move apart – these occur mostly
at the mid-ocean ridge. (creation of valleys)
Divergent Boundary
Convergent Boundary
• Two plates come together causing a
collision.
Convergent
Transform Boundary
• A place where two plates slip past each other,
moving in opposite directions. Earthquakes occur
frequently along these boundaries.
Today – NASA’s Role
• The LAGEOS II satellite, built by the Italian
Space Agency, Agenzia Spaziale Italiana (ASI),
and managed by NASA's Goddard Space Flight
Center, measures crustal movement by using
Satellite Laser Ranging technology
Today
• Residents of warm southern California are moving to
Alaska whether they like it or not. Scientists, using the
theory of plate tectonics, say that southern California is
moving north and will collide with Alaska in
approximately 150 million years.
Predictions for the Future:
• What can scientists predict about some of the features of
the Earth existing today? Quite a lot. The Atlantic Ocean
will continue to expand, while the Pacific Ocean
(originally Panthalassa Ocean) will shrink. Eventually, the
Mediterranean Sea (remnant from the Tethys Sea) will
disappear, connecting Africa with Europe. India will
continue to push into the southern Asian continent, pushing
the Himalayas higher. Meanwhile the city of Los Angles
will continue its journey north to join with the city of San
Francisco. This will take several million years to occur.
Maybe in another 200 million years there will be no need
for a transoceanic trip from America to Asia.