Download Unit 2 - Plate Tectonics

Unit 2 - Plate Tectonics
Mantle – the layer of Earth between the crust and the core. It is the largest of Earth’s layers.
Crust – the rocky outer layer of Earth.
Plate – a rigid section of Earth’s crust that moves very slowly. Earth’s crust is divided into
approximately 15 plates.
Plate tectonics – the movement of plates that make up the surface of Earth.
Four Types of Boundaries
Convergent boundary – a boundary between plates that are moving toward each other.
Crust is destroyed in a convergent boundary as one plate slides below another.
Convergent boundaries are also known as subduction zones.
Collisional boundary – a type of convergent plate boundary where two land masses are
moving together. Mountains are created.
Divergent boundary – a boundary between plates that are moving away from each other.
New crust is created in a divergent boundary. Divergent boundaries on the ocean floor
result in long mountain ranges called mid-ocean ridges.
Transform boundary – a boundary between plates that are sliding past one another.
Earthquake – shaking and vibration of Earth’s surface.
Lithosphere – the rigid upper layer of the Earth. The lithosphere consists of the crust and the
upper part of the mantle.
Volcano – an opening in Earth’s crust from which magma (molten rock), gas, and ash erupt.
Continental drift – the theory that the continents are moving very slowly. Alfred Wegener
proposed continental drift in 1915. Wegener found evidence that the continents were once
joined together in a giant supercontinent he called Pangaea. His theory states that, when
Pangaea broke up, the continents slowly drifted to their current positions.
Pangaea – an ancient supercontinent that scientists believe existed from about 200 to 300
million years ago.
Fossil – the remains, traces, or imprint of an ancient living thing preserved in rock. Fossils can
be bones, shells, impressions, or even footprints.
Glacier – a large, slowly moving body of snow and ice.
Ice age – a time when Earth was very cold and large areas were covered by glaciers.
Landmass – a large, unbroken area of land.
Earthquake – shaking and vibration of Earth’s surface. Earthquakes release energy in the form
of seismic waves.
Fault – a fracture in Earth’s crust where the rocks on either side have moved.
Epicenter – the point on Earth’s surface directly above the focus, or origin, of an earthquake.
Focus – the point within Earth where an earthquake originates.
Seismic wave – a vibration produced by an earthquake.
P wave – one of two types of body waves that are produced by earthquakes. P waves are the
fastest seismic waves, and will arrive at a location before other seismic waves. As a P wave
passes through a material, the material moves back and forth parallel to the direction that the
wave is moving. The “P” in P wave stands for “primary.”
S wave – one of two types of body waves that are produced by earthquakes. S waves are
slower than P waves. As an S wave passes through a material, the material moves up and
down perpendicular to the direction that the wave is moving. The “S” in S wave stands for
“secondary.”
Seismogram – a graphical record of ground vibrations. Seismograms are made by instruments
called seismographs.
Seismograph – an instrument that measures and records ground vibrations.
The Ring of Fire is a zone of frequent earthquakes and volcanic eruptions that encircles the
Pacific Ocean. It is 40,000 km long. 90% of the world's earthquakes occur along the Ring of
Fire.
The plate tectonic theory arose out of two separate geological observations: continental drift,
noticed in the early 20th century, and seafloor spreading, noticed in the 1960s.
Constructed Response Answers
Alfred Wegener’s idea of continental drift proposes the possibility that the continents came from
a single land mass called Pangaea. Upon observing the similarities in the fossil, animal, plant,
and soil records shared by Africa and South America, and the similarities in the coastlines of
these two continents, Wegener proposed that these continents must have been united in the
past. The reasoning: if these two continents shared similarities of plants and animals, it was
impossible for these animals to have swum across the Atlantic Ocean, so, the continents must
have been joined once upon a time.
In 1962 Harry H. Hess proposed that the seafloor was created at mid-ocean ridges, spreading in
both directions from the ridge system. At the spreading center, magma rises from the earth's
mantle. When the magma hardens, it forms new oceanic crust that becomes welded to the
original crust. Abundant evidence supports the seafloor-spreading theory.
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First, samples of the deep ocean floor show that basaltic oceanic crust becomes
progressively younger as the mid-ocean ridge is approached,
Second, the rock making up the ocean floor is considerably younger than the
continents.
Third, magnetic surveys conducted near the mid-ocean ridge showed elongated
patterns of normal and reversed polarity of the ocean floor in bands paralleling the
ridge.