Transcript 1.2 outline Continents change position over time I. Continents join together and split apart 1) 2) Alfred Wegener proposed the theory of continental drift Continental drift: hypothesis that Earth’s continents.

1.2 outline
Continents change position over
time
I. Continents join together and split
apart
1)
2)
Alfred Wegener proposed the theory of
continental drift
Continental drift: hypothesis that
Earth’s continents are moving apart from
a single landmass (Pangaea)
A. Pangaea and Continental Drift
1)
Pangaea: all continents joined together
to create huge supercontinent
II. The theory of plate tectonics explains how
plates and their continents move
A.
Evidence from the Sea Floor
1) Mid-ocean ridges: huge underwater
mountain ranges where new oceanic crust is
created
2) Sea-Floor spreading occurs when melted
rock is pushed up to create new oceanic
crust; old crust is pulled away to make room
for new material
A. Evidence from the Sea Floor (cont.)
3)
4)
Age of Sea Floor shows that the
youngest rock is closest to the ridge,
while the oldest rock is farthest away
Ocean Trenches are deep canyons in the
sea floor. Dense oceanic crust is being
destroyed here; old crust is being
destroyed at the same rate as the new
crust is forming
B. Causes of Plate Movement
1)
2)
Convection: heat transfer by the
movement of material
Convection current: when the hot, soft
rock rises, cools and sinks, then is
heated and rises again
C. Putting the Theory Together
1)
2)
3)
Theory of plate tectonics: states that
Earth’s lithosphere is made up of huge
plates that move over the surface of the
Earth
Two plates moving apart are the South
American and African plates
Two plates pushing together are the
South American and Nazca plates
C. Putting the Theory together (cont.)
4)
5)
Two plates scraping past each other are
the North American and Pacific plates
Where tectonic plates meet, major
earthquakes, volcanoes, and mountain
ranges appear
Review Answers
1)
2)
sea-floor spreading, different ages of
rocks, mid-ocean trenches & ridges
Circulation of heated and cooled material
forms convection currents that can carry
tectonic plates.