Drifting Continents and Spreading Seas The Road To Plate Tectonics.
Chapter 8: Plate TectonicsChapter 8: Plate Tectonics 8.1: Earth has several layers 8.2: Continents...
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Transcript of Chapter 8: Plate TectonicsChapter 8: Plate Tectonics 8.1: Earth has several layers 8.2: Continents...
Chapter 8: Plate Chapter 8: Plate TectonicsTectonics
8.1: Earth has several layers
8.2: Continents change position over time
8.3: Plates move apart
8.4: Plates converge or scrape past each other
8.3: Plates move apart8.3: Plates move apart Before, you learned:
The continents join and break apart The sea floor provides evidence that
tectonic plates move The theory of plate tectonics helps explain
how the plates move
Now, you will learn: About different plate boundaries What happens when plates move apart How the direction and speed of plates can
be measured
Tectonic plates have different Tectonic plates have different boundariesboundaries
Plate boundary: where the edges of two plates meet
Types of boundaries: Divergent boundary: where plates move
apart…mostly found in the ocean Convergent boundary: where plates push
together Transform boundary: where plate scrape past
each other
The sea floor spreads apart The sea floor spreads apart at divergent boundariesat divergent boundaries
Also called spreading centers
As the ridges continue to widen, a gap called a rift valley forms Molten material rises to form
new crust
Mid-Ocean Ridges and Rift Valleys Mid-Ocean Ridges: like a long
chain of mountains. Rift Valley at center
magnetic reversal animation
Divergent Boundaries – Mid-Divergent Boundaries – Mid-Ocean Ridges and Rift ValleysOcean Ridges and Rift Valleys
World’s longest ridge: Mid-Atlantic Ridge Length of the ocean The North and South American plates are moving
away from the Eurasian and African plates 11, 000km (6214 mi) from Iceland to Antarctica 24 km (15 mi) wide and 9 km (6 mi) deep
Sea-Floor Rock and Magnetic Sea-Floor Rock and Magnetic ReversalsReversals Scientists studied the sea floor rock
and were surprised by a discovery they made about the Earth’s magnetic field
Think of Earth as a bar magnet, with a N and S pole (not the geographic pole)
Poles switch places: Magnetic Reversal Caused by changes in the magnetic
field
animation
Each magnetic Each magnetic reversal is reversal is
recorded in sea-recorded in sea-floor rockfloor rock
Magnetic materials in the new rock line up with the Earth’s magnetic field
The material hardens and those minerals are permanently fixed in the directions pointing north and south
Date the rocks, and can have further evidence of plate movement
Most recent reversal: 760,000 years ago
Animation
More animations
http://www.edumedia-sciences.com/en/a108-earth-s-magnetic-field
Continents split apart at divergent Continents split apart at divergent boundariesboundaries
Continents also spread apart at divergent boundaries
Boundary begins to form when hot material rises from deep in the mantle Heat causes the crust to bulge
upward Crust cracks, a rift valley forms Magma rises through the
cracked, thinned crust forming volcanoes
Rift valley grows wider, the continents begin to split apart
The thinned valley floor sinks lower and lower until it is below sea level Water may fill the valley
Hot Spots can be used to Hot Spots can be used to track plate movementstrack plate movements
Hot spots: where heated rock rises in plumes (thin columns) from the mantle Volcanoes often develop above
the plume Often far from plate boundaries,
but offer a way to measure plate movement
Heat from the plume partly melts some of the rock in the tectonic plate above it: eventually the rock above will melt
A volcano will form at the surface of the plate in time Rises above the sea: an island
Movement: can measure direction and speed of plate movements
The lithosphere is The lithosphere is made up of many made up of many
platesplates
Ex: about ½ the African Plate lies under water
1) have the continents always been where they are today?
2) if not, how did they move to their present positions…
Mystery Solved! - Section 1.2