Download 10.1 Continental Drift

10.1 Continental Drift
Continental Drift
10.1 Continental Drift
Wegener's Hypothesis
· proposed by Alfred
Wegener in 1912
· hypothesized that all
continents were once a
supercontinent called
Pangea
began breaking apart
250 million years ago
continents drifted to
their current locations
Evidence for Continental Drift
1. Jigsaw Puzzle
continental shorelines fit together like puzzle
pieces
2. Fossils
matching fossils found on different landmasses,
but could not have crossed the oceans
ex. Mesosaurus
3. Rock type and structure
mountain chains on the coastline of one
continent continue on continents across the
ocean
ex. Appalachian Mtns.
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Missing Evidence
· Wegener could not provide an
acceptable mechanism for the
movement of the continents
· Wegener's hypothesis declined
· proof came a few decades later
when scientists discovered sea
floor spreading
Mesosaurus
4. Ancient climates
ancient glaciers in warm climates or tropical
species in Antarctica
Mid-Ocean Ridges
· undersea mountain ranges with a crack, or rift, in
the center through which magma rises
· sediment closer to the ridge is younger than
sediment farther from the ridge
· oldest oceanic rock = about 175 million years old
Sea-Floor spreading
· proposed by Harry Hess
· named by Robert Dietz
· process by which new ocean lithosphere (sea
floor) is formed as magma rises to Earth's
surface and solidifies at a mid-ocean ridge
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video
10.1 Continental Drift
Review: Earth's Magnetic Field
· the movement of Earth's liquid iron core produces
a magnetic field around Earth
· compass needle points to the geomagnetic North
Pole
Geomagnetic Reversal Time Scale
· normal polarity - rock's magnetic field points north
· reversed polarity - rock's magnetic field points south
· alternating patter of normal and reversed polarity
when rocks are placed in chronological order
Review Questions
1. Who proposed the idea of continental drift?
2. List the 4 pieces of evidence supporting CD.
3. Why was CD declined?
4. Who proposed the theory of sea-floor spreading?
5. What is sea-floor spreading?
6. What evidence(s) supports sea-floor spreading?
Paleomagnetism
· residual magnetism in rocks
· as magma cools on the
sea floor, iron-rich minerals
align with Earth's magnetic
field
· magnetic orientation
(direction) become
permanent when rock
hardens
Magnetic Symmetry
· magnetic patterns on each side of a mid-ocean
ridge are symmetrical
· allows scientists to date rocks
· discovered that new rocks form at the center of
a ridge and move away in opposite directions
· provided proof for Hess's sea-floor spreading
idea and Wegener's continental drift hypothesis