The document discusses plate tectonics and the structure of the Earth. It explains that Earth's outer layer is divided into plates that move over Earth's mantle in a constant state of motion. This motion of plates causes continental drift and is responsible for geological features and events like earthquakes, volcanic eruptions, and mountain building. The theory of plate tectonics developed in the 1960s to explain phenomena like sea floor spreading and the movement of continents over geologic time.

1. Name: ______________________________
PASS OBJECTIVE 5. Earth/ Space Science Notes
Objective 1: Earth has four main systems that interact: the atmosphere, the hydrosphere, the biosphere, and
the geosphere.
PLATE TECTONICS
THE GEOSPHERE
 The geosphere is in a constant state of motion that gives rise to movement of the continents.
 The unifying theory that explains how continental drift is possible is called plate tectonics, which was
developed by geologists in the 1960s.
 Earth has four layers
 Outermost layer is the crust.
 Solid layer that flows slowly like putty is the mantle.
 Outer core— molten metal above the inner core.
 Inner core— dense iron core; very hot and dense.
Plate boundaries are edges where plates meet.
 Tension can pull plates apart, resulting in new lithosphere forming in the gaps.
 Colliding plates could cause mountains to form as rock crumbles and folds.
 Subduction occurs when a denser plate sinks underneath a less dense plate.
 Shearing causes faults and earthquakes as two plates slide past each other.
GEOLOGY—the study of planet Earth
 Geologists – scientists who study the forces that make and shape planet Earth
 Landforms – features formed in rock and soil by water, wind and waves
Studying surface changes
 Constructive forces – shape the surface by building up mountains and landmasses.
 Ex: land is made
 Destructive forces – slowly wear away mountains and other land features.
 Ex: land is destroyed
A Journey to the Center of the Earth –
Plate Tectonics Notes pg.1

2.  Temperature – at a depth of about 20m the temperature gets warmer as you go deeper into the
earth’s interior. For every 40 m, the temperature rises 1degree C, then it eventually increases
more slowly.
 Pressure – the deeper you go the greater the pressure (force pushing on a surface of area)
Describe how there is convection in the Earth’s surface __________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Evidence for Continental Drift
 Alfred Wegener (1880-1930), a German meteorologist and geologist, was the first person to propose
the theory of continental drift.
 200 mya the continents were originally joined together, forming Pangaea, meaning "All-earth".
Evidence from landforms
 Mountain range – in Africa matched a mountain
range in South America
 European coal fields match coal fields in North
America
Using the picture to the right, explain why fossils of
Mesosaurus were found in Africa, when he cannot
swim and it is far away from South America today.
___________________________________________
_______________________________________________________________________________________
_
_______________________________________________________________________________________
_
 Wegener could not provide a satisfactory explanation for the force that pushes or pulls continents
 geologists rejected the theory (until new evidence was discovered later.)
SEA FLOOR SPREADING
 Mid-ocean ridge – longest chain of mountains in the world
 Where volcanic and earthquake activities occur
 Rift Valley – runs lengthwise through
 the mid-ocean ridge
The Theory of Sea Floor Spreading:
 Harry Hess in 1960
 The ocean floors move like conveyer belts, carrying the continents with them.
Plate Tectonics Notes pg.2

3.  Since the continents are attached to the ocean floor, sea-floor spreading could be the force
causing the continents to move.
 At mid-ocean ridges molten material rises from the mantle and erupts.
 The molten material then spreads out, pushing older rock to both sides of the ridge.
 Evidence from Molten Material – scientists discovered “pillow lava” forming along the mid-ocean
ridge. These rocks form when molten material hardens quickly after erupting under water.
 Evidence from Magnetic Stripes – patterns of magnetic stripes match on either side of the mid-ocean
ridge, suggesting that the ocean floor is spreading evenly in opposite directions.
 Evidence From Drilling Samples – The Glomar Challenger, a drilling ship, drilled holes in the ocean
floor. Discovered that rocks along mid-ocean ridges are much younger than rocks farther away.
SUBDUCTION at deep ocean trenches
 Subduction – process whereby the ocean floor plunges into the mantle and melts at deep
underwater canyons called deep-ocean trenches.
 Subduction and Sea-Floor Spreading work together like a conveyor belt, moving the
continents.
Types of Plate Movements
 Divergence, Convergence, and Transform
 At the boundaries of the plates, various deformations occur as the plates interact;
 they separate from one another (seafloor spreading),
 collide (forming mountain ranges),
 slip past one another (subduction zones, in which plates undergo destruction and remelting), and slip
laterally.
 Seafloor spreading is the movement of two oceanic plates away from each other,
 results in the formation of new oceanic crust (from magma that comes from within the Earth's
mantle)
 Happens along a a mid-ocean ridge.
 Where the oceanic plates are moving away from each other is called a zone of divergence.
When two plates collide, some crust is destroyed in the impact and the plates become smaller. The results
differ, depending upon what types of plates are involved.
 Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a
relatively light, thick continental plate, the oceanic plate is forced under the continental plate; this
phenomenon is called subduction.
 Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and
magma from the mantle rises, forming volcanoes in the vicinity.
 Two Continental Plates - When two continental plates collide, mountain ranges are created as
the colliding crust is compressed and pushed upwards.
When two plates move sideways against each other, there is a tremendous amount of friction which
makes the movement jerky.
 The plates slip, then stick as the friction and pressure build up to incredible levels.
 When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.
Plate Tectonics Notes pg.3

4. Plate Tectonics Notes pg.4