Vocabulary on Continental Drift

and Plate Tectonics

Plate Tectonics The pieces of Earth's lithosphere are in slow, constant motion and float on convection currents in the mantle.
Continental Drift This is a theory developed by Alfred Wegener that states that Earth's plates were once one huge landmass  and over years they were broken apart and drifted to their present location.
Pangaea The name that Alfred Wegener gave to Earth's one huge landmass that existed 300 million years ago.  It means all Earth.
Alfred Wegener A German scientist that developed the theory of continental drift.  He did not have any proof although he based his theory on the fact that the continents looked like pieces of a puzzle that fit together.
Fossil A trace of an ancient organism (animal or plant) that has been preserved in rock.
Give 3 pieces of evidence for the continental Drift Theory on separate index Cards Puzzle evidence: the edges of the continents fit together like puzzle pieces (Africa and South America)

Land features: Mountain Ranges and coal fields line up on various continents (for example: European coal fields line up with similar coal fields in North America)

Fossil Evidence: Glossopteris, Lystrosaurus, Mesosaurus see details below

Climate Evidence: Fossils of tropical plants were found on Spitsbergen, an island in the Arctic Ocean.  When those plants were there it must have been closer to the equator.

Ocean Floor Evidence: In the 1960's scientist were able to study the ocean floor with technology, such as sonar.  This enabled them to see evidence of sea-floor spreading.  This actually showed how the plates were being pushed apart.  They had evidence from molten rock, magnetic stripes on the ocean floor and drilling rock samples.


Glossopteris A fossil of a seed from a fern plant.  This seed fossil was found on the continents of Africa, South America, Australia, India, and Antarctica.  This seed was too heavy to be carried by wind or water.  The continents must have been connected at one time.
Lystrosaurus and Mesosaurus  Fossils of a hippo-like creature and a reptile.  These fossils were found on continents that are separated by great oceans and neither animal could swim those distances.  Therefore the continents must have been connected at one time.
Plate Boundaries The edges of Earth's plates where two or more plates meet
Convergent Boundaries When two plates move toward each other.  There are two types:

Convergent boundaries of plates of the same density:  When two continental plates collide or two oceanic plates collide.  A mountain will form and the older more dense rock will subduct - be pushed back into the mantle to melt!

Convergent boundaries of plates of different density:  When a continental plate collides with an oceanic plate.  A trench will form on the side of the oceanic plate and a mountain or volcano might form on the continental plate.  Subduction of the oceanic plate will occur because it is more dense.

Divergent Boundaries When two plates move apart: Ocean floor Spreading occurs.  New ocean floor is formed.  A mid-ocean ridge forms and a Rift valley forms.
Strike-Slip Boundary/Transform Fault When two plates move past each other or up and down.  An earthquake will occur here.  This can also be called a fault or fracture zone.
Ocean Floor Spreading This occurs at divergent boundaries where new ocean floor is formed.
Convection Currents The movement of material caused by changes in temperature.  This occurs in the mantle due to the heat from the core below and the cool temperature of the crust.  When magma is near the core the heat makes it less dense so it rises; when it nears the crust it cools and falls.  This movement of magma, breaks the lithosphere up and moves the plates.
Rift Valley The flat space between the mid-ocean ridges at a divergent boundary, it consists of new ocean floor.
Trench A v-shaped valley formed at a subduction zone (convergent boundary)
Mid-ocean Ridge Underwater mountain chains - formed at a divergent boundary due to the piling up of magma.
Subduction When denser rock is pushed down into the mantle so that it melts back into magma.  This occurs at convergent boundaries.