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Continental Drift, Plate Tectonics, and Volcanoes.


Scientist who came up with the theory of Continental Drift.No one believed at first, because he couldn't explain how the continents moved.

Continental Drift

The theory that states that all Earth's continents were once a single landmass called Pangaea.


The one single landmass scientists believe existed before the continents broke apart.

Harry Hess

The scientist that came up with the theory of seafloor spreading.

Seafloor Spreading

The theory that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches.

Thoery of Plate Tectonics

The theory that says Earth's crust and rigid upper mantle are broken into enormous slabs called plates.

Plate Boundaries

Areas where tectonic plates interact.

Convergent Boundaries

Places where tectonic plates are moving towards one another.

Divergent Boundaries

Places where tectonic plates are moving apart from one another.

Transform Boundaries

Places where 2 plates slide past each other horizontally.


When plates meet and 1 of the 2 plates is is forced benath the other.

Rift Valleys

Divergent boundaries that occur on land


The internal resistance to flow (how "sticky" a substance is).

Andesitic Magma

Forms from crust being sub-ducted, pushed down, into the Earth's mantle. This magma type has an intermediate viscosity.

Basaltic Magma

Forms from rock in the upper mantle melting. This magma type has a low viscosity.

Rhyolitic Magma

Forms from molten material rising and mixing with the crust above it. This magma type has a high viscosity


Large Craters

Shield Volcanoes

These produce mountains with a broad, gently sloping side and a nearly circular base.

Cinder-Cone Volcanoes

These volcanoes have steep sides and are generally small.

Composite Volcanoes

These are much larger then Cinder-Cone Volcanoes.


Rock fragments thrown into the air during an eruption.

Pyroclastic Flow

Rapidly moving tephra and volcanic ash that moves down the volcano.

Hot Spots

Volcanoes found far away from plate boundaries.

Gondwanaland or Gondwana

Large continent in the southern hemisphere. Included the land now found in South America, Africa, Antarctica, India, & Australia

Early Evidence for Plate Tectonics

Jigsaw-like fit of Africa and South America (early mapmakers), matching rock formations on opposite sides of the Atlantic Ocean, same fossils on multiple continents, fossils indicating had different climate in past


Land-dwelling animal found on different continents and could not swim to get there.


Freshwater reptile that could not have swum ocean, yet is found on different continents.


Fern that grew in temperate climates, similar to our climate. Yet, fossils of the fern have been found in cold Antarctica and equatorial India.

Past Climate Based on Coal

Coal, made from swamp plants, has been found in Antarctica & indicates Antarctica was warmer at one time. Was it closer to equator?


Measures small changes in magnetic fields


Study of Earth's magnetic field, based on magnetic iron of basalt on the ocean floor. The iron lines up and "points" in the direction of the Earth's magnetic field when the magma cooled and formed rock.

Magnetic Reversal

Change in Earth's magnetic field. The iron in the basalt on the ocean floor indicate the Earth's magnetic field has reversed several times.

Magnetic Symmetry

Opposite sides of an ocean ridge have mirror-image patterns of magnetic reversals.


Line on a map that connects points of equal age that were formed at the same time. Isochron maps have been used to map the age of the ocean floor - Figure 17-11 p.453

Convection (As it relates to plate tectonics)

Transfer of energy by the flow if a heated material. Convection currents in the asthenosphere (soft, plastic-like part of mantle) are thought to cause plate movement. Convection cycle rises at the mid-ocean ridges of divergent boundaries and sinks at the deep-sea trenches of convergent bondaries.

Folded (Very High) Mountains

Extremely high mountains formed when 2 continental plates converge (collide). Because the continental plates have similar density there is no subduction and plates are crumpled & forced up instead.

Island Arc

Formed above an oceanic-oceanic convergent boundary when volcanoes become tall enough to break the surface of the water. Examples: Aleutian Islands, Japan, Phillipines

Deep Sea Trench

Formed at convergent boundaries when subduction occurs and the more dense oceanic plate slips under another plate. The deepest one is by the Mariana Islands.

Rift Valley

Divergent boundary on lad where continental crust begins to separate or "tear apart"

Ocean Ridge

Divergent boundary in ocean where seafloor spreading occurs as magma rises, cools, forms new rock, forcing the 2 plates apart.


When one plate is forced to sink below the other. The plate that sinks does so because it is more dense.

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