Download Evolution of the Earth

Earth’s Evolution
The Lithosphere
• The Lithosphere
is divided into
several large
plates.
• Convection
currents in the
asthenosphere
move the plates.
PLATE TECTONICS
- explains observations of past and present geological processes
- example of the development and acceptance of a scientific theory, as some
revolutionary scientific theories may take years or decades to win general acceptance.
A theory explaining the structure
of the earth's crust and many
associated phenomena as resulting
from the interaction of rigid
lithospheric plates that move
slowly over the underlying mantle.
Moving Plates
• Plates are in constant motion, travelling
at a few centimetres per year.
• The ocean floors are continually
moving too.
• Convection currents beneath the plates
move the plates in different directions.
• The source of heat driving the
convection currents is radioactive
decay which is happening deep in the
Earth.
Continents seem to be able to fit together…
Coincidence?... Or were they once connected…
1858 Geographer Antonio Snider-Pellegrini made these maps
Alfred Wegener
1912
German meteorologist.
He was the first to suggest the
hypothesis of continental drift to
explain Pellegrini’s observations
that continents fit together like
puzzle pieces.
PANGEA
Continental Drift: states that
parts of the Earth's crust slowly
drift atop a liquid core
LINK
1. Evidence from Fossils
• Animals living today on distant continents
(ex: Africa & South America) are all
different from one another.
• Fossils show that animals and plants long
ago were similar however. This implies the
continents were connected.
• In the millions of years since separation,
species evolved differently on different
continents.
• Tropical fossils are found in many polar
areas suggesting that those places were
once closer to the equator.
Wegener’s evidence for Continental Drift
2. Evidence from Glaciation
• “Scratches” made on bedrock by
glaciers on different continents “line”
up when the continents are placed
together.
• This suggests that the continents
were connected when the striations
were made
• Evidence of glaciers is found in
tropical areas suggesting that those
areas were once further north or
south.
3. Evidence from rock and mineral
formations
• Coal deposits had been found in Antarctica.
• Coal deposits only form in the tropics suggesting
that Antarctica had once been in the tropics.
• Rock composition in certain areas does not
match surrounding rock but does match rock
type of a distant continent.
– Ex: Rocks of Northern Newfoundland do not match
North America, but are similar in structure and
composition to those of Scotland. This suggests that a
small bit of what is now Scotland became attached to
NA when the two split.
1930
Wegener left for Greenland to
find more evidence to support
his hypothesis.
He was never seen again.
This is the last photo of
Wegener taken with a native
guide.
His continental drift
hypothesis was hotly
debated for the next 30
years.
Most active tectonic events occur at plate boundaries.
Map shows that most
earthquakes (black, grey)
and volcanoes (red) are
concentrated at plate
boundaries
What else is attributed to plate tectonics?
Tsunamis
Changing landscapes
Mountain building
Volcanic eruptions
New seafloor and
mineral deposits
What are the
“side effects”
of plate
tectonics?
Mineral formation
Sedimentary deposition / erosion
Animal/plant life
Ocean circulation
Climate
Courtesy AGS
Plates meet at Plate Boundaries
• Boundaries have different
names depending on how
the two plates are moving
in relationship to each
other:
• 1) Convergent Boundary
• 2) Divergent Boundary
• 3) Transform Boundary
1) Convergent Plate Boundary
1. Oceanic plate has crashed into a
continental plate.
2. Folding and bending of the plates
causes earthquakes.
3. Continental plate folded into a
mountain.
4. Oceanic plate is more dense and
is forced under the continental
plate.
5. Some of the rock in the Oceanic
plate melts as the plate sinks.
The melted rock rises up causing
earthquakes and volcanic
eruptions.
Example of a Convergent Plate
Boundary
• South America:
• Oceanic Nazca Plate collides
into the South America plate.
• Formed the Andes Mountains
(volcanoes along the mountain
crest)
• Formed a deep trench off the
coast in the Pacific Ocean.
2) Divergent Plate Boundaries
• Plates are being pulled apart by
convection currents in the
asthenosphere.
• As the plates separate along the
boundary, the block between the
faults cracks and drops down into
the soft, plastic interior (the
asthenosphere).
• New crust is formed along the
boundary.
• Earthquakes occur along the
faults, and volcanoes form where
the magma reaches the surface.
Example of a Divergent Plate Boundary
Mid Atlantic Ridge
• Mid-Atlantic Ridge is a
Divergent Plate
Boundary.
• Over 15000 km long.
• Average height of 3km.
3) Transform Boundary
• Places where plates slide past
each other.
• Transform boundaries are not
marked by spectacular surface
features, but their sliding motion
causes lots of earthquakes.
• Example: San Andreas fault.
The slice of California to the
west of the fault is slowly
moving north relative to the rest
of California.
• The San Andreas fault is
the border between two
tectonic plates—the North
American Plate and Pacific
Plate. Los Angeles is
located on the Pacific Plate,
and San Francisco is on the
North American Plate. In a
few million years, the two
geographic areas will be
right next to each other
because the western side of
the fault (the Pacific Plate) is
moving northward with
respect to the rest of the
state. The fault is moving at
about 2 centimeters (just
under an inch) per year.
•
•
•
•
•
ANIMATIONS OF:
Three types of boundaries
Rifting
Formation of earth’s crust
Hot Spot Volcanoes