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Continents
ChangePosition
Over Time
Chapter 1
Lesson 2
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Continents Join Together and S
The Earths surface is constantly moving
We know this because of changing mapsover time
In 1912, German scientist Alfred Wegenerproposed a hypothesis called
This hypothesis stated that Earths continents
were once joined in a
and
gradually moved/drifted apart
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Evidence for Contin
1. Wegener learned
that the fossils of one dinosaur, wasdiscovered in both South America andAfrica. The fossils were NOT foundanywhere else in the world. This can beexplained if South America and Africawere once joined.
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Evidence for Contin
2. Greenland
today lies near the Arctic Circle and is
mostly covered in ice. However, fossils oftropical plants can be found on its shores.Another example is South Africa. We knowthat Africa has a warm climate, but itsrocks were deeply scratched by ice sheetsmillions of years ago.
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Evidence for Contin
3.
Wegeners best evide
make up the continenother. Rocks in Brazil mfound in western Africain the Appalachian MAmerica] matched thScotland.
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Pangaea and Contin
is the huge
supercontinent that included all of ourcontinents today
Long ago, all the continents were a singleland mass until they started to split apart[200 million years ago]
However he was unable to explain HOWthe continents moved
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The Theory of Plate Tectonics exp
plates and their contine
until the mid 1900s, whenscientists proved that tectonicplates moved!
arehuge underwater mountainranges; they are present inevery ocean and circles theentire Earth [seams of abaseball]
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Evidence from the
2.
Scientists drilled into t
obtained rock samplrevealed that the yothe ridge, while the oaway
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Evidence from the
3. Why isnt the
Earth getting larger if the sea-floor isspreading? The answer is OCEAN TRENCH.At these ocean trenches, dense oceaniccrust is sinking into the asthenosphere. Oldcrust is being destroyed at the same rateas the new crust forming.
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Causes of Plate M
Because tectonic platasthenosphere [hot taconvection; energy tramovement of a mater
SOFT ROCK in the asthcools, and sinks [denseheated and rises agai
inside a pot]
This sinking and rising m
transfers heat energy i
This is a VERY SLOW proyear]; but over a millio
distance!
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Causes of Plate M
also help
move huge plates
Slab pull occurs when gravity pulls a cool,dense plate down into the asthenosphere
Ridge push occurs when material from amid-ocean ridgeslides downhill FROM the
ridge
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Putting the Theory
Geoknoabomovthe
This Eartup oove
The
areAntIndiNazAmplat
Whetheyearerupmee
plat