1.
Continental Drift- The idea that the continents drifted to their present positions over millions of years a.
Theory of Alfred Wegener i.
Noticed continents fit together like pieces of a puzzle ii.
Could not prove how continents moved, but was able to find evidence that they did move:
1.
Fossil Clues— a.
Glossopteris—fossilized tropical plants found in polar regions today b.
Mesosaurus—fossils found on many of the present continents—but there would have been no possible way they could have crossed oceans. The land had to be connected.
2.
Climate Clues-- a.
Coal Deposits of Siberia—Coal forms in tropical places but deposits are found all over the globe where it’s freezing or cold. b.
Glacial Striations—Glaciers scratch up rock as they grind over them. Glacial striations have been found in many places on the earth that are warm and tropical.
3.
Rock Clues-- The Appalachian Mountains are made of the same exact types of rocks with identical mineral compositions as the Caledonian Mountains of Europe.
They must have been connected long ago.
2.
Sea Floor Spreading—The idea that new material is constantly being added to the sea floor and that old material is constantly being recycled in the mantle. a.
Theory of Harry Hess i.
Mid ocean ridges are cites on the ocean floor where magma from the mantle is forced upward through the crust of the sea floor. As it cools, it hardens to form new crust.
1.
The newer material is less dense—lighter, the older material is more dense— heavier. a.
Evidence of Sea Floor Spreading i.
Magnetic clues
1.
The Earth acts like a magnet. When the magma that is forced through the mid ocean ridges hardens into rock, minerals orient themselves according to the magnetic field of the earth. When pole reversals occur—they are recorded in the mineral grains of the ocean floor as “magnetic stripes.” a.
Because reversals are rare, scientists can gauge how much time has passed between them. i.
They can use this info to figure out how long it took the continents to move to their present day positions.

3.
Theory of Plate Tectonics—The idea that the plates of the earth move in relation to one another. a.
Sections of the crust are divided into plates. i.
Continents and oceans rest on these plates. ii.
The plates float on a plastic like layer of the mantle. b.
Plates are made of crust and part of the upper mantle known as the lithosphere. i.
100 km thick ii.
Less dense than material below it --called the asthenosphere--so it floats like a raft on it. c.
Plate boundaries – When plates move they interact with other plates in various ways: i.
Plates moving away from each other form Divergent Boundaries
1.
Form mid ocean ridges or rift valleys.
2.
Magma pushes to the surface and forms new land or volcanoes. ii.
Plates moving toward each other form Convergent boundaries
1.
Older material on the sea floor is dense and moves under another tectonic plate. a.
Subduction zone—Dense oceanic plate sinks under a less dense continental plate i.
The older material is very dense, so it subducts below the newer material
1.
Forms a trench a.
Mariannas Trench—7 miles deep. The deepest place on the earth.
2.
Volcanic islands form at subduction zones a.
Aleutian islands b.
Japan b.
Mountain Ranges are thrust upward as two continental plates collide a.
Andes Mountains b.
Himalaya Mountains iii.
Plates sliding past one another form Transform Boundaries
1.
Very earthquake prone—the most stress and tension on existing rock occurs as transform boundaries. a.
San Andreas fault in California/