Download Chapter 10 Section 1 Notes

Chapter 10 Section 1 Notes
Continental Drift
Like a Puzzle
1. Similarity of the continental shorelines on
either side of the Atlantic ocean.
Like a Puzzle
2. The east coast of South America seems
to fit perfectly into the west coast of
Africa.
Alfred Wegener
1. In 1912, a German scientist
hypothesized that the continents once
formed part of a single landmass called a
supercontinent.
Alfred Wegener
2. The supercontinent began breaking up
into smaller continents about 250 million
years ago (during the Mesozoic Era).
Alfred Wegener
3. Over millions of years these continents
drifted to their present locations.
WEGENER’S EVIDENCE
•
Fossil Evidence
1. Fossils of the same plants and animals were
found in both South America and western
Africa.
WEGENER’S EVIDENCE
•
Fossil Evidence
2. Fossils of the Mesosaurus, a small, extinct
land reptile, are found in both South America
and western Africa.
WEGENER’S EVIDENCE
•
Fossil Evidence
3. It was unlikely that these reptiles had swam
across the Atlantic ocean.
WEGENER’S EVIDENCE
•
Rock Formations
1. The ages and types of rock in western Africa
and in eastern South America match closely.
WEGENER’S EVIDENCE
•
Rock Formations
2. Mountain chains that ended at the coastline
of one continent continue on other
continents across the ocean.
WEGENER’S EVIDENCE
•
Rock Formations
3. The Appalachian Mountains extend
northward along the eastern coast of North
America and are of similar age and structure
of mountains in Greenland, Scotland, and
northern Europe.
WEGENER’S EVIDENCE
•
Climatic Evidence
1. Changes in climatic patterns suggest that
the continents have not always been located
where they are now.
WEGENER’S EVIDENCE
•
Climatic Evidence
2. Geologists have found layers of debris from
ancient glaciers in southern Africa and South
America.
WEGENER’S EVIDENCE
•
Climatic Evidence
3. Fossils of tropical plants have been found in
areas that now have colder climates.
WEGENER’S EVIDENCE
•
Missing Mechanisms
1. Other scientists of the time rejected the
mechanism by which Wegener proposed
that the continents moved.
WEGENER’S EVIDENCE
•
Missing Mechanisms
2. Wegener suggested that the continents
plowed through the rock of the ocean floor.
WEGENER’S EVIDENCE
•
Missing Mechanisms
3. There was no geologic evidence supporting
Wegener’s idea that the continents plowing
through the ocean floor. Wegener died in
1930 never founding an acceptable
mechanism.
Mid-Ocean Ridges
1. What are they?
•
Undersea mountain ranges through the
center of which run steep narrow valleys.
Mid-Ocean Ridges
2. 1st trend: The sediment that covers the
sea floor is thinner closer to a ridge than
it is farther from the ridge.
Mid-Ocean Ridges
3. 2nd trend: The ocean floor is youngest at
the mid-ocean ridges and grow older as
you mover farther away from mid-ocean
ridges. Rocks on land are as old as 3.8
billion years old, while the oldest oceanic
rocks are only 175 million years old.
Sea-Floor Spreading
1. In the 1950’s, Harry Hess suggested that
the valley at the center of the ridge was a
crack in Earth’s crust where new sea
floor was being created
Sea-Floor Spreading
2. Hess suggested that if the ocean floor is
moving, the continents must be moving
too. He thought that sea-floor spreading
was the mechanism that Wegener had
failed to find.
Paleomagnetism
1. As magma solidifies to form rock, ironrich minerals in the magma align with
Earth’s magnetic field in the same way
that a compass needle does.
Paleomagnetism
2. When the rock hardens, the magnetic
orientation of the minerals becomes
permanent. This residual magnetism of
rock is called paleomagnetism.
Magnetic Reversals
1. Earth’s magnetic field has not always
pointed north. Rocks with magnetic
fields that point north are normal polarity,
while rocks with magnetic fields that
point south are reversed polarity.
Magnetic Reversals
2. There is a pattern of normal and
reversed polarity in the rocks of the
ocean floor. Scientists used this pattern
to create the geomagnetic reversal time
scale.
Magnetic Symmetry
1. The striped magnetic pattern on one side
of a mid-ocean ridge is a mirror image of
the striped pattern on the other side of
the ridge.
Magnetic Symmetry
2. The patterns indicate that the youngest
rocks are at the center of a ridge and the
older rocks are farther away on either
side of the ridge.
The End !!!