Science section 3 earth

continental drift

at one time, all the continents were joined together in a single land mass called Pangaea

plate tectonics

since Wegeners time, scientists have pieced together the theory of plate tectonics

-the lithosphere is broken up into plates

-convection currents in the mantle cause the plates to move very slowly

diverging boundary

plates move apart.

• new crust forms from rising magma.

• an underwater mountain range called a ridge forms

• sometimes, volcanoes grow above the surface

converging boundary

plates move together

subduction

if one or both plates are oceanic, subduction occurs

• one plate is forced under the other and melts into magma

• an underwater valley called a trench forms

• mountains and volcanoes may form

transform boundaries

plates slide sideways past each other

mountain

a mountain is part of earths surface that is much higher than the land around it

mountain range

a mountain range is a series of mountains

• mountains form when tectonic plates collide

formation of fold and fault mountains

• when plates collide, heat and compression cause the layers of sedimentary rock to fold and break

• bends that form in rock are called folds

• an anticline is an upward fold

• a syncline is a downward fold

• large cracks that form from breakage are called faults