The theory of plate tectonics is the unifying theory that explains Earth’s geological processes. • How does the movement of Earths tectonic plates cause observable changes and effects? • How does tectonic plate movement effect you locally? Student Objectives Statement Beginning Approaching Meeting Succeeding Exceeding I can describe the layers of the Earth (crust, mantle, outer core, inner core) I can describe the types of plate boundaries (convergent, divergent, and transform) I can describe how volcanoes and trenches form I can describe how mountain ranges form I can describe how earthquakes occur I can relate tectonic processes to local geological events I have an earthquake safety kit Summary of Key Points Continental Drift Theory • Various pieces of evidence indicate that the continents were once joined but later drifted to their current positions. 1. The continental shelves of the continents can be aligned like a jigsaw puzzle. 2. Regions of some continents that are far apart have similar rocks, mountain ranges, fossils, and patterns of paleo-glaciation. Plate Tectonics Theory and Convection • The process of sea floor spreading provides a mechanism for continental drift. 1. The continents are attached to huge slabs of rock, known as tectonic plates. Earths Layers and Convection • Earth has distinct layers. • When the tectonic plates move across Earth’s surface, they carry the continents with them. Plate Interactions • Convection currents from the asthenosphere push magma to Earth’s surface, causing tectonic plates to move and sometimes converge. • When tectonic plates converge, one plate may slide beneath the other or the edges of the plates may crumple, forming mountains. • Tectonic plates can also diverge, or spread apart, forming rifts on land and ridges in the oceans. Volcanoes and Earthquakes • Tectonic plates may begin to slide past one another at a transform boundary, resulting in the build-up of pressure, which may be released as an earthquake. • Volcanoes occur at tectonic plate boundaries or over geologic hot spots, where magma is coming up through Earth’s crust.
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The theory of plate tectonics is the unifying theory that ... · The theory of plate tectonics is the unifying theory that ... Continental Drift Theory • Various pieces of evidence
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The theory of plate tectonics is the unifying theory that
explains Earth’s geological processes.
• How does the movement of Earths tectonic plates cause observable changes and effects?
• How does tectonic plate movement effect you locally?
Scientists have used many separate lines of evidence to determine how the continents might once have fit
together. In this activity, too, will use various pieces of evidence to reconstruct the supercontinent Pangea.
Question: How did the continents fit together before Pangea broke apart?
Materials:
• Photocopy of continents
• Scissors
• 21.5 cm x 28 cm sheet of paper
• glue
Procedure: 1. Obtain a photocopy of the continents from your teacher. Cut out each continents, trimming the
pieces just to the edge of the dotted lines. The dotted lines represent the true continental edges,
the continental shelves.
2. Use the clues provided in the legend below and the shapes of the continents to help you
reconstruct Pangea. Piece together the continent shapes into a supercontinent on a separate piece
of paper, but do not glue them down yet.
3. Once you assembled your pieces, check with your teacher before gluing them on to the blank
sheet of paper.
4. Copy the legend below onto the paper with your map of Pangea.
5. Clean up and put away the materials you have used.
Analyze: 1. Which continents were easiest to fit together? Explain why.
2. Of the pieces of the evidence that you used to reconstruct Pangea, which provided the best clues
as to how the continents were once joined? Justify your answer.
3. a) Were there any pieces of Pangea that you found difficult to place?
b) If so, what other evidence would have helped you to place these pieces?
Conclude and Apply: 1. a) In a few sentences, summarize the steps you took to reconstruct Pangea.
b) How was the process you took similar to the method Alfred Wegener used to support
continental drift theory?
2. Why did you use several pieces of evidence to reconstruct Pangea, not just one?
3. a) Hypothesize where the continents might have be situated in 200 million years.
b) Describe how ecosystems of British Columbia’s west coast might change as a result. Justify
your answers.
Theory of Plate Tectonics 1. Wegener’s evidence for continental drift did not explain how entire continents could change
locations, so his theory was rejected by scientists of his time.
2. Wegener and the other scientists of his time did not know that Earth’s surface is broken into
large, rigid, movable slabs of rock called tectonic plates that slide over a layer of partly molten
rock.
3. New scientific equipment developed since the 1940s has allowed scientists to gather evidence
from the sea floor and THE MID-OCEAN RIDGE.
Evidence from mapping the sea floor: When explorers began to map the ocean floor, they
discovered undersea mountain running north to south down the length of the Atlantic Ocean,
which they named the Mid-Atlantic Ridge.
Evidence from ocean rock and sediments: Rocks taken from the Mid-Atlantic Ridge were
younger than other ocean rocks.
Evidence from paleomagnetism: The direction of Earth’s magnetic polarity can experience a
magnetic reversal over thousands of years
J. Tuzo Wilson combined the concepts of sea floor spreading and paleomagnetism to explain
continental drift, laying the groundwork for the Plate Tectonic Theory:
• The Plate Tectonic Theory states that Earth’s surface is broken into large plates that
move apart and then rejoin, sliding over the semi-fluid rock below.
• There are about 12 major tectonic plates and many smaller ones.
• Mantle convection is thermal energy transfer in the mantle where hot, light magma rises
and cold, dense magma sinks. This rotation of magma cause movement of the plates
(**this is the one question Wegener could not answer)
• Heat to keep the mantle molten comes from radioactive elements.
A geologic hot spot is the location of excess radioactivity, causing magma to rise to Earth’s
surface. Also referred to as Mantle Plume.
The Hawaiian Islands formed as a tectonic plate passed over a hot spot and magma rose up from
under Earth’s surface.
Quick Check #2
1. Why were Wegener’s ideas about continental drift originally rejected? ______________________________________________________________________________