Review – Chapter 8 & 9 – Plate Movements
From Science Probe 7
Key Idea: Earth is made up of four layers – the crust, the mantle, the outer core, and the inner
core.
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crust: the think layer of solid rock that makes up Earth’s outermost layer (p. 219)
mantle: a hot thick layer of solid and partly melted rock (moves sluggishly like thick
syrup) (p. 219)
outer core: dense, hot region that is made up mostly of liquid iron and some nickel (p.
220)
inner core: a large ball of iron and nickel, pressure from the weight of the other layers
keeps the material solid even though the temperature is almost as hot as the
temperature on the surface of the Sun (p. 220)
Key Idea: Wegener developed his theory of continental drift
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Pangea: Wegener suggested that a very long time ago, the continents were all part of
one supercontinent called Pangea (p. 221)
Wegener’s developed his theory based on evidence – the shape of the continents,
fossils, landforms and an ancient ice age (p. 221)
Key Idea: Scientists now have additional evidence for the theory of plate tectonics
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mid-ocean ridge: the ridge of mountains is about 50000 km long and runs through the
middle of the oceans (p. 226)
theory of plate tectonics: the surface of the Earth consists of about a dozen large plates
that are continually moving (p. 228)
continental crust: the parts of the Earth’s crust that have continents on them (p. 228)
oceanic crust: the parts of the Earth’s crust that have only ocean floor on them (p. 228)
Key Idea: Moving plates interact at all three types of boundaries
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divergent boundaries: the boundary between plates that are moving apart (p. 237)
convergent boundaries: boundaries where plates move towards each other (p. 240)
o subduction zone: when plates come together, one plate sinks below the other;
this occurs at a subduction zone (p. 240)
o oceanic plate converging with continental plate: when an oceanic plate collides
with a continental plate, the oceanic plate is subducted under the continental
plate, which creates deep ocean trenches along the edge of a continent (p. 240)
o oceanic plate converging with oceanic plate: when two oceanic plates converge,
one plate sinks below the other and trenches are formed at the subduction zone
(p. 241)
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o continental plate converging with continental plate: when two continental plates
meet, neither is subducted causing the crust to buckle and crumble pushing up
mountains or areas of high level ground called plateaus (p. 242)
transform fault boundaries: plates that are slipping past each other (p. 243)
Key Idea: Earthquakes are caused by the sudden movement of plates at plate boundaries
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earthquakes: the sudden release of energy causes vibrations of Earth’s crust (p. 246)
earthquakes at divergent boundaries: hot magma rises below the crust pushing upward
toward an opening, pressure builds up where the plates are joined and suddenly the
pressure is enough to push the plates apart causing the crust to shake (p. 246)
earthquakes at convergent boundaries: when an oceanic plate is subducted under
another oceanic or continental plate it may get stuck against the top plate, the force
builds up until the top plate suddenly moves causing a large earthquake (p. 247)
earthquake at transform fault boundaries: when two plates are moving past each other
in opposite directions along a transform fault boundary they sometimes get stuck, the
force builds up until one plate suddenly moves causing an earthquake (p. 247)
epicentre of an earthquake: the point on the surface of Earth directly above the focus
(the location within Earth where the earthquake started)
seismic waves: shock waves sent out when an earthquake occurs (p. 248)
aftershocks: smaller tremors that can occur any time for months after an earthquake as
the pressure within the Earth’s crust is gradually released (p. 248)
tsunamis: ocean waves caused by an earthquake or an underwater volcano (p. 250)
Key Idea: Volcanoes can erupt at plate boundaries or at hot spots
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volcano: any opening in the Earth’s crust through which molten rock and other material
erupt (p. 255)
volcanoes at divergent boundaries (often occur on the ocean floor): magma pushes to
the surface where plates are moving apart, the lava erupts and cools to form a ridge on
each side of the crack on the ocean floor, some of these ridges rise high enough to reach
the surface and create an island (this is how Iceland was formed) (p. 256)
volcanoes at convergent boundaries (most volcanoes on land are located at convergent
plate boundaries): one plate is being subducted under another plate often creating a
powerful volcanic eruptions (Mount St. Helens) (p. 257)
volcanoes that form near hot spots: hot spots are parts of the mantle where the
temperature is much higher than normal, magma collects in enormous pools and
eventually melts a hole in the rock above it and pours out of the hole onto Earth’s
surface as lava; the lava flows like a river and hardens, it’s not explosive (this is how the
Hawaiian islands were formed) (p. 258)