Transcript Continental Drift – hypothesis that states the continents were once

Continental Drift Hypothesis – Wegner believed
continents had once been joined, and over time they drifted apart
Pangaea – the first super-continent
• Alfred Wegner 1912
Presented early fossil
evidence
• No evidence to explain how
or why continents moved
• Continental Drift Theory
later developed into the
theory of Plate Tectonics
Evidence supporting Continental Drift
a) Continental Puzzle –
continents fit together
b) Matching Fossils matching fossils
(Mesosaurus) on cross
ocean landmasses
c) Mountain chains and
rock type –
(Appalachian)
d) Ancient climates – (ice
core data, scratched
bedrock)
Plate Tectonics Theory
Earth's outermost layer, the lithosphere, is broken into 7
large, rigid pieces called plates: the African, North American, South American,
Eurasian, Australian, Antarctic, and Pacific plates. Several minor plates also exist, including the
Arabian, Nazca, and Philippines plates.
• plates are
moving ~ 5 cm
per year in
different
directions and
speeds
• The place where
the two plates
meet is called a
plate boundary
•Plates are crust
and upper mantle
Plate Boundaries and Actions
•Seafloor spreading produces new lithosphere
•San Andreas Fault is an example of a Transform Fault
•East African Rift Valley is an example of a divergent plate boundary
•Himalayas are an example of convergent continental/continental plates
Evidence and Testing for Plate Tectonics
• Paleomagnetism –
changing patterns of
magnetized rocks
• Earthquake patterns –
link between plate
boundaries and
earthquakes
• Ocean Drilling - age of
seafloor sediment
– Newest (ridge crests)
– Oldest (continental
edges)
• Hot Spots – show plates
move over Earth’s
surface (Hawaii)
Cause of Plate Motion (tectonics)
• Heat convection in the
mantle is the basic cause
of plate movement
• Slab Pull and Ridge Push
– downward convective
flow of lithosphere
(plate boundaries)
• Mantle Plumes – upward
convective flow
(volcanoes, hot-spots)