Chapter 12 – Science 10
 Continental drift theory
 Earthquakes
 Hot spot
 Magnetic revearsal
 Paleoglaciation
 Plate tectonic theory
 Spreading ridge
 Tectonic plate
 Volcanoes
 20th Century German Scientist – Alfred Wagner
 Jigsaw Puzzle Fit
 “Supercontinent” called Pangaea
 Greek words pan, meaning all & gaea, meaning Earth
 Continental shelves match across oceans
 Wagener analyzed and reasoned:
 Mountain ranges begin on one continent, end at the
coastline, and then appear to continue on another
continent across the ocean so continents must have once
been attached.
 Wegener studied the fossils of Mesosaurus
 Mesosaurus was a fresh water reptile
 Fossils found only in 2 places:
 Southeastern South America
 Southwestern Asia
 Could the small reptile swim 6000 km of open ocean?
 Land dwelling animal fossils even more convincing
 Cynognathus and lystrosaurus
 Fern Fossil
 Glossopteris
 Found all over the planet even Antarctica!
 Antarctica must have once been near the equator.
 When glaciers retreat they leave a mark
 Valleys, deeply scratched rocks etc..
 Evidence of glaciers in what is now the equator area
 Coal deposits
 Only occur where life once thrived
 Found in Antarctica!
 Earth is divided into movable slabs of rock called
tectonic plates
 Related to Volcano locations
 Related to where Earthquakes occur
 The depth of oceans and the Mid Atlantic Ridge
 A massive underwater mountain range
 The worksheet is your passport.
 Oceanographers studied the age of the ocean floor
 Discovered the youngest rocks were found closest to
the ridge in the ocean.
 More sediment (becoming thicker) the farther the
rock was away from the ridge.
 Earth has magnetic poles like a bar magnet
 Poles can reverse: magnetic reversal
 Not really known why!
 Probably because the liquid core changes direction
 Happens 4-5 times every million years
 Rocks as they are formed keep their “magnetic
needles” inside them frozen in place as they cool
 A pattern of stripes of the iron direction of rocks was
discovered on both sides of the ridge!
 Harry Hess, 1960 tied it all together!
 Magma from inside Earth rises
 Rises because it is hot and less dense then the material
surrounding it
 Magma cools and hardens when it breaks through the
surface
 This happens at the spreading ridge
 This is the new sea floor!
 As hot magma rises it pushes away the magma that
cooled earlier!
 Like a conveyor belt
 See Table 12.1!
 Combined the concepts of
sea floor spreading and
paleomagnetism into the
theory of continental drift
 Introduced the idea of hot
spots
 Chains of volcanic islands
were formed when a
tectonic plate passed over
a stationary molten area of
hot rock in the Earth
 Continents must break up at certain areas , move
across the Earth’s surface, and then rejoin!
 This would explain where mountains form,
earthquakes happen and where we find volcanoes
 Also explains the how rocks get recycled inside the
Earth.
 Rocks can transform from one type into another
 Wilson’s theory became known as the Plate Tectonic
Theory.
 VIDEO