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6th grade science - plate tectonics

McDougal Littell Science
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How did Earth's layers form?
Earth's layers formed as denser materials sank toward the center and the less dense materials rose toward the surface.
What are Earth's main layers?
The core, the mantle and the crust
The core is Earth's densest region and is made of up of two parts.
Inner core and the outer core
Inner Core
a ball of hot, solid metals. It remains solid because of enormous pressure.
Outer core
a layer of liquid metals that surround the inner core. the lower pressure allow's the metals to remain a liquid.
The mantle
Earth's thickest layer is made of hot rock that is less dense than the core
The crust
a thin layer of cool rock that surrounds Earth.
continental crust
includes all the continents and some major islands
oceanic crust
includes all the ocean floors. the crust is home to all life on Earth.
Earth's crust and top of mantle
Lithosphere and Asthenosphere - the lithosphere sits on top of the Asthenosphere
Lithosphere
made up of the curst and the very top of the mantle and is the most rigid of all layers.
Asthenosphere
a layer of hotter, softer rock in the upper mantle, it is soft enough to flow slowly
Tectonic Plates
the lithosphere is broken into many small slabs of rock. Most large plates include BOTH continental crust and oceanic crust
Why do you see only the dry land areas of tectonic plates on a typical world map?
The oceanic crust of the plates is underwater.
Continental Drift
A hypothesis made by Alfred Wegener that Earth's continents were once joined together in a single landmass and gradually moved or drifted apart.
From what three sources did Wegener gather evidence for his continental drift hypothesis?
Fossils
Studies of ancient climate
The geology (rocks) of continents
What is Pangaea?
Wegener's name for when the continents were once joined together in a huge supercontinent.
Comes from Greek word meaning "all lands"
Mid-Ocean ridges
Huge underwater mountain ranges
Evidence for The Theory of Plate Tectonics
Sea-Floor Spreading, Age of the sea floor, Ocean trenches
Sea-floor spreading
molten rock that rises through cracks in the crust, cools, and forms new oceanic crust.
Age of sea floor
rock is youngest near the ridge, and older as you get farther away, showing that older rock was carried away from the ridge some time ago.
Ocean trenches
Huge trenches like deep canyons, in the sea floor where the dense ocean crust is sinking into the asthenosphere.
Causes of Plate Movement
Convection and Convection currents
convection
energy transferred by the movement of a material.
convection currents
The hot, soft rock rises, cool and sinks, then is heated and rises again.
Theory of Plate Tectonics
The theory that states that Earth's lithosphere is made up of huge plates that move over the surface of the Earth.
One plate cannot move without affecting the others nearby.
The plates can move apart, push together, or scrape past each other.
Plate movements cause most major earthquakes, volcanoes and mountain ranges.
Plate Boundary
Is where the edges of two plates meet.
What are the three types of boundaries?
Divergent boundary
Convergent boundary
Transform boundary
Divergent Boundary
A boundary along which two tectonic plates move apart, characterized by either a mid-ocean ridge or a continental rift valley.
Most divergent boundaries are found in the ocean.
Convergent Boundary
A boundary along which two tectonic plates push together, characterized either by subduction or a continental collision.
Transform Boundary
A boundary along which two tectonic plates scrap past each other and crust is neither formed nor destroyed.
What features are found at divergent boundaries in the ocean?
Mid-ocean ridges
Rift Valleys
Rift Valleys
A deep valley formed as tectonic plates move apart, such as along a mid-ocean ridge.
What are the longest chains of mountains on Earth?
Mid-ocean ridge
What happens to the old crust as new crust is formed?
The old crust is split and pushed aside, forming horizontal cracks. The old crust forms part of the ridge.
What happens in a magnetic reversal?
Earth's magnetic north and south poles switch places.
Magnetic reversal
A switch in the direction of Earth's magnetic field so that the magnetic north pole becomes the magnetic south pole and the magnetic south pole becomes the magnetic north pole.
Where is each magnetic reversal recorded?
In the sea-floor rock
Explain how records of magnetic reversals show that plates move apart
The farther away from the ridge, the older the record of reversals on both sides of the ridge. This shows that the plates move away from the center.
Continental divergent boundaries
Continents spread apart at a divergent boundary.
It forms when hot material rises from deep in the mantle.
This heat causes the crust to bulge upward and the crust crakes as it is stretched and a rift valley forms.
What happens when the floor of a rift valley sinks below sea level?
The valley can be flooded by waters from nearby oceans or rivers, eventually forming a lake or sea.
Hot Spots
An area where a column of hot material rises from deep within a planet's mantle and heats the lithosphere above it, often causing volcanic activity at the surface.
How were the Hawaiian Islands created?
Are being built as the Pacific Plate moves slowly over a hot spot.
How do you know which island or landform was formed first?
The island or landform farthest from the hot spot was formed first. As the plate moves, it carries the islands or landforms away from the hot spot; therefore, the ones first to form are the farthest away.
How does a hot-spot volcano form?
A plume of magma from the mantle melts the rock in the plate above it until a volcano forms.
Subduction
The process by which an oceanic tectonic plate sinks under another plate into Earth's mantle
Continental-Continental Collision
A boundary along which two plates carrying continental crust push together
Both crusts are the same density; neither plate can sink beneath the other
When does folded crust form mountains?
When it is pushed up high
Explain how colliding plates form mountain ranges
Plates push together until rocks crumple and fold, rising higher and eventually forming mountain ranges
Oceanic-Oceanic Subduction
A boundary along which a plate carrying oceanic crust sinks beneath another plate with oceanic crust
Deep-ocean trenches - these trenches are like deep canyons that form in the ocean floor as a plate sinks
Island Arcs - chains of volcanic islands that form on the top plate, parallel to a deep-ocean trench
Oceanic-Continental Subduction
A boundary along which a plate carrying oceanic crust sinks beneath a plate with continental crust
Deep-ocean trenches - as the oceanic crust moves it causes underwater earthquakes
Coastal mountains - as oceanic crust sinks under a continent, the continent crust buckles to form a range of mountains
Why do deep-ocean trenches form at both types of subduction?
In both types of subduction, one plate sinks beneath another, forming a deep-ocean trench.
Where do two plates move past each other in opposite directions?
At transform boundaries
Where do transform boundaries occur?
Mostly on the sea floor near mid-ocean ridges
On land
Tectonic Plate Boundaries
Transform Boundaries
Divergent Boundaries
Convergent Boundaries
What future events can scientists predict using the theory of plate tectonics?
Sites of future volcanoes
Earthquakes
Mountain building
Transform Boundaries
plates scrape horizontally past each other; crust is neither formed nor destroyed
Divergent Boundaries
as plates move apart, new crust is built, forming mid-ocean ridges and rift valleys
Convergent Boundaries
crust is destroyed where plates subduct; it is folded where plates collide