12.1 Evidence for Continental Drift – Student Notes
 Wegener came up with the ____________________________________________
• the idea that the continents used to be connected as one big supercontinent but
slowly moved apart over time
 He named the original supercontinent ______________________.
Evidence for Continental Drift
1. The Jigsaw Puzzle Fit
 The continents do not fit “perfectly” like a jigsaw puzzle.
 A better fit is found by matching the ___________________________________
(original shorelines that are now underwater)
2. Matching Geological Structures and Rocks
 ______________________________________ of one continent, end at coastline 
begin again at another continent
(similar folds, ages)
 Similarities between rocks of adjacent continents are evidence for continental drift.
 The rocks found in Newfoundland are the ____________________________________
as rocks found in Greenland, Ireland, Scotland, Norway.
3. Matching Fossils
 The fossils of some ancient species suggests evidence for ‘pangaea’.
 Wegener found fossils of a fresh-water reptile ‘________________________’ in two
places: SE South America and SW Africa
 Glossopteris (a fern) Found In: South America, Africa, Australia, India Antarctica
4.
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Glacial Evidence
Evidence of glaciers formed in ice ages provides support to CD theory
During ice ages, glaciers covered large areas of land
When the glaciers ___________________________________, they leave behind proof
Deeply scratched rocks (___________________), U-shaped valleys, patterns of rock
formations
 ___________________________ refers to the extent of ancient glaciers and to the rock
markings they have left behind
5. Climatic Evidence
 Coal forms from __________________________ (usually tropical swamp material)
 Since the South Pole has never had a tropical climate....it must have been in a
___________________ location than it is now
How the Continents Move
 The current theory is that the continents moved due to the ________________________
_________________________________.
 _________________________________ = movable slabs of rock that make up the Earth
 These large rigid plates slide over the surface of Earth (over a layer of partially molten
rock)
 Tectonic plates explain the location of volcanoes and earthquakes....
 Volcanoes are ___________________________________________________________
_______________________________________________________________________
 Earthquakes are _________________________________________________________
_______________________________________________________________________
The Mid-Atlantic Ridge
 Mapping of the ocean floor revealed a __________________________________ running
down the middle of the Atlantic Ocean.
 It is called the “Mid-Atlantic Ridge”
How It Was Formed
 The tectonic plates of the Earth slide apart (sliding is called “_____________________”)
 Another way to think of this is “_______________________________”
 Something must replenish this lost crust!
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Areas of oceanic crust are replenished by _________________________________....
Magma (molten rock) rises up
Cools and hardens when it reaches surface
Forms the new sea floor
 This process keeps going.....
 Convection currents cause more magma to ________________
 Magma ____________________________ hardened material
 Older rock is pushed aside as new rock forms!
 “__________________________________________”
Proof of Sea-Floor Spreading
 In the 1940’s...oceanographers took samples of rock from the Mid-Atlantic Ridge
 ________________ rocks were found closer to ridge
 ________________rocks were found farther from ridge (and in thicker layers...built up!)
 Scientists have also found that the rocks themselves have a
“__________________________________”
 To understand this, we must understand the Earth’s magnetism....
 Every few thousand years....the direction of magnetic field REVERSES!
 “__________________________________________”
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Rock contains metals like iron (Fe)
Little pieces of iron “_______________________” with magnetic field and then they
STAY that WAY!
When MAGNETIC REVERSAL happens...they line up in opposite direction.
Rocks “______________________” the direction of the Earth’s magnetic field that
existed when the rock formed! Amazing!
 Studying the magnetic properties of ancient rocks....“____________________________”
 So the sea floor is spreading and new rocks (from magma) are formed...
 Looking closely at the sea floor, scientists found a striped pattern!
Hot Spots
 A geological area where molten rock rises to Earth’s surface!
 __________________________ were formed by a tectonic plate passing over a hot spot.
 The plate slides in the direction of the arrow....forms a ________________ of islands!