(c) mcgraw hill ryerson 2007 12.1 evidence for continental drift if you look closely at a world map....

(c) McGraw Hill Ryerson 2007

12.1 Evidence for Continental Drift

• If you look closely at a world map. It looks likes S. America and Africa can fit together.



• Early maps of the world caused Alfred _________ to propose the ____________________________. The continents looked as though they might fit together like puzzle pieces.

The continental shelves actually fit together even better. The large mountain ranges and coast lines match up. Each continent has a

continental shelf Continent Continental shelf Ocean floor

All continental shelves are approximately 200m deep.

See pages 506 - 509


The original, supercontinent was named _________ by Wegener.

Wegener also realized that other evidence also supported his theory.1. There were ___________________________ and ________

on different continents.• Rocks in Newfoundland are the same type rock

with the same age as the rocks in Norway and Sweden

2. There were _________ _________, like Mesosaurs, on different continents.• Similar fossils found at similar depths in Africa

and South America. Plants and animals are only found in very specific locations around the world.



3. There was evidence of different climates (eg. glaciers) on warm continents.•Fossils of warm weather plants found in

Antarctica Glacial rock in S. America and Africa.

• Ice ages show the retreat of large icebergs. These icebergs leave behind deep valleys and scratches in the ground.

•There is coal in Antarctica – coal comes from decaying tropical swamp land. If Antarctica was a swamp land then it must have been in another location on the earth.



Quick Check

1. What did Wegener notice about the shapes of continents that led him to suggest that continents were able to move? ______________________________________________________________

_______________________________________________________________________2. List three forms of evidence besides continent shape that gave support to the idea of

continental drift.________________________________________________________________________________________________________________________________________________________________________________________________________________________


Continental drift theory - Pangea breaking apart


How Can Continents Move?

• Wegener’s evidence for continental drift didn’t explain

how entire continents could change locations. New scientific equipment ( ________) allowed scientists to measure the

slow, but steady, drift of Earth’s tectonic plates. It was noted that ____________ and ____________ appear in certain

patterns, which happen to be along the ______________________ ___________________.

Mapping of the ocean floor revealed the __________________, a long mountain range running down the middle of the Atlantic ocean.

See pages 510 - 512


Rocks taken from the Mid Atlantic ridge were ______________ than other ocean rocks.

Sediments along the Ridge became ________________________ ____________ from the ridge.

_______________________ shows that iron-based rocks along the ridges are striped with reversing magnetic fields.

All of these findings developed the

Theory of _______________________

How Can Continents Move?


Sea Floor Spreading


Sea Floor Spreading: An Explanation

• Hess suggested that magma rose to form new rock at certain places. Magma (melted rock), rises and falls like warm and cold liquids. The __________________________________ formed a

_______________________ where it broke through Earth’s crust. Like a “new crust” conveyer belt Magnetic striping of basalt rock shows long stripes of new rock

moving away from ocean ridges, and also reveals the direction of Earth’s magnetic field at that time. This magnetic field changes or reverses over time.

See pages 512 - 513


• Wilson then unified the ideas of Wegener and Hess into the plate tectonic theory. Continental drift occurs because of areas like these ridges, that

push along tectonic plates floating on Earth’s surface. geologic ______________ are anywhere magma rises to Earth’s

surface.• A geologic hot spot is the location of ____________________, causing

magma to rise to Earth’s surface. – The __________ Islands formed as a tectonic plate passed over a hot

spot and magma rose up from under Earth’s surface.


Plate Tectonics - 1960


Quick Check

Quick Check1. Explain the implications of evidence from each of the following areas.(a) mapping the sea floor _________________________________________________________________________________________________________________________________________________________________________________________________________________(b) analyzing ocean rock and sediments _____________________________________________________________________________________________________________________________________________________________________________________________________(c) paleomagnetism _____________________________________________________________________________________________________________________________________________________________________________________________________________________2. How did the Hawaiian Islands form? _______________________________________________________________________________________________________________________________________________________________________________________________________________3. What does the theory of plate tectonics state? _______________________________________________________________________________________________________________________________________________________________________________________________________

(c) mcgraw hill ryerson 2007 12.1 evidence for continental drift if you look closely at a world map....

Documents