Continental Drift Continental Drift and Sea Floor and Sea Floor Spreading Spreading Chapter 17 Chapter 17
Dec 31, 2015
Continental Drift and Sea Continental Drift and Sea Floor SpreadingFloor Spreading
Chapter 17Chapter 17
Continental DriftContinental Drift
• In 1912 Alfred Wegener came up with the hypothesis
– The continents were all one
– Called Pangaea
Continental DriftContinental Drift• Pangaea
– Super continent– Existed during the
Permian Period– North half called
“Laurasia”– South half called
“Gondwanaland”
Continental DriftContinental Drift
• Wegener had 4 major pieces of evidence for his theory
1. Similar rocks found in Africa and South America
2. Glaciation and Ancient Climates
3. Fossils
4. Continents seem to fit like puzzle pieces
Continental DriftContinental Drift
1. Similar Rocks in Africa and South America– Rocks on both coasts are the same kind– 2 continents must have been joined when
rocks formed
Continental DriftContinental Drift2. Glaciation/Ancient
Climates• During
Carboniferous period
• Glaciers in India, South Africa, South America and Australia
• Northern hemisphere was warm and tropical
Continental DriftContinental Drift
3. Fossils• Mesosaurus = aquatic (shallow) reptile
Continental DriftContinental Drift
3. Fossils• Glossopteris = fern
that liked cold climates that has large seeds that do not spread out well
Continental DriftContinental Drift4. Continents fit like
puzzle pieces• First looked at
South America - looked like it would fit like a puzzle piece into Africa
• Most continents fit together
Continental DriftContinental Drift
• Wegener tried to explain why and how the continents moved
• He thought that the continents plowed through the ocean floor
• This was physically impossible
• So the other scientists of the time didn’t believe him
Sea Floor SpreadingSea Floor Spreading• Enter Harry Hess (1962)
• Naval Officer• Used Fathometer
(measures depth)• Took a map of the sea
floor• Noticed mountains
and valleys in the ocean
Sea Floor SpreadingSea Floor Spreading
• He proposed a theory to explain mid-ocean ridges– The magma wells up from deep inside the Earth
and forms new rocks.– Some rocks contain minerals that are magnetic.– When the rock forms it records the direction of
Earth’s magnetic field.– Like a compass, the rocks “point” towards
magnetic north.– From the rocks we know that the earth’s
magnetic field has reversed over time.
Sea Floor SpreadingSea Floor Spreading
• From this theory, he could estimate age of land
• And the speed of movement of plates• Noted that if new crust is formed, there must
be a place where old crust is destroyed• It is a continuous cycle• Even though new crust is forming, the Earth
remains the same size!