12.1 Evidence for Continental Drift Student Notes

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 à 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. 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!

 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!

 “______”

 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!