Transcript Chapter 17 Notes

Chapter 17 Notes
I. Continental Drift
A. Early mapmakers noticed matching
coastlines
B. Single landmass theories
1. Suess-(late 1800s) Austrian geologist theorized
that the southern continents were once joined in a
body called Gondwonaland
2. Wegener-(1912) German scientist who proposed
that all continents were once joined in a body
called Pangaea
C. Evidences for plate tectonics
1. Rock formations with shared rock
types, ages, and orientations
a) Appalachian Mountains with
Greenland and Europe
b) South America and Africa
• Appalachian
Mountains
and the
Caledonide
Mountains in
Greenland &
Europe
2. Fossil evidences:
a) Mesosaurus, a freshwater animal found on
widely separated continents
b) Labyrinthodont; land-dwellers found
on widely separated continents.
c) Glossopteris;
fossil seed fern
found on widely
separated
continents
3. Climate evidence
a) Coal deposits found in Antarctica.
Coal forms in warm, tropical areas.
Climate Evidences con’td
b) Glacial
deposits and
striations (long
parallel
scratches)
found in the
Sahara Desert.
D. Wegener’s theory was rejected by
the scientific community. Why?
1. He had no explanation for HOW
the continents could have moved.
2. Even if he could have explained
that, the question still remained-How
could continents move without
breaking apart?
II. Seafloor Spreading
A. Technology
1. RADAR (Radio Detection and Ranging) and
SONAR (Sound Detection and Ranging) were
developed during WWII. After the war ended,
they were modified for scientific use.
2. Magnetometer can detect very small changes in
magnetic fields. Magnetic field reversals were
detected worldwide.
A. Topography of the Ocean Floor
1. No longer thought to be just a wide, flat plain
2. Underwater trenches (deep enough to submerge
Mount Everest!!) and mountain chains that
encircle the entire earth were discovered.
B. Rocks & Sediments
1. Old rocks were found near the continents, young
rocks near the ocean ridges
2. Thick sediments were found near continents,
almost none near the ocean ridges at center of
oceans.
D. Magnetism
1. The use of magnetometers during repeated
crossings of the worlds’ oceans revealed a
pattern of magnetic reversals over time.
2. Magnetic Symmetry – Each side of the
mid-ocean ridge is a mirror image of the
other. Magnetic stripes parallel to the ridge
can be paired with magnetic reversals
discovered in rocks on land. This helps to
determine the ages of seafloor rocks.
III. Plate Tectonics & Boundaries
A. Plate Tectonics – a new theory emerged
which combined Wegener’s old ideas of
Continental Drift and the new theory of
Seafloor Spreading.
B. Data began to emerge about three types of
plate boundaries (edges.) They are:
1. Divergent
2. Convergent
3. Transform
A. Divergent Boundaries
1. Plates move apart
2. On land, this is called a Rift Valley
Example: African Rift Valley
3. Under the sea, it is known as a Mid-Ocean ridge.
Example: Mid-Atlantic Ridge
B. Convergent Boundaries – collisional
1. Continent – continent
Mountain building
Example: India and Eurasia colliding is
still building the Himalayan Mts.
2. Continent – oceanic
Violent volcanoes and deep-sea trenches
(Subduction)
Example: Pacific plate and North America
colliding to produce Mt.St.Helens, Ranier,
Hood, etc in the pacific northwest
3. Oceanic – oceanic
Produces underwater volcanoes
Example: Pacific plate and Japan
C. Transform Boundaries
Plates slide past one another.
Example; San Andreas Fault in California