Transcript Continental Drift

Chapter 4.1
1.Continental Drift
a.A hypothesis stating that the continents
once formed a single landmass, broke
up, and drifted to their present
locations.
b.Proposed by a German Scientist named
Alfred Wegener.
c. Pangaea
i.The name that Wegener gave to
the solid land mass formed by all
continents.
ii.It means “all lands”.
e. Panthalassa
i.The name that Wegener gave to
the single ocean that surrounded
Pangaea.
ii.It means “all seas”.
225 MYA
150 MYA
200 MYA
65MYA
PRESENT DAY
a.Wegener hypothesized that Pangaea
began breaking up during the
Mesozoic Era and forming our current
landmasses we know as continents.
b.He also believed this motion
crumpled the land in areas forming
mountains.
2. Continental Drift Evidence
a.The edges of our current continents fit
together much like a puzzle.
b.Fossils of the same land animals, from
270 million years ago, have been found
in Eastern South America and Western
Africa. It would have been impossible
for these animals to swim across the
Atlantic Ocean.
c. Geologic evidence of age and type
of rocks in the coastal regions of
Western Africa and Eastern Brazil
match closely.
i.Mountain chains that end at the
coastline of one continent continue
on landmasses across the ocean.
1.The Appalachians extend northward
along the eastern United States and
mountains of similar age and structure
are also found in Scotland and
Northern Europe. If these landmasses
are observed in Pangaea, they fit
together.
i.Coal deposits have been found in the
United States, Europe, and Siberia that
indicate a subtropical to tropical climate.
d. Glacial evidence also proves that
Pangaea once existed.
i.Glacier debris has been found in
Southern Africa and South America,
areas that are to warm to have glaciers.
e. While we now know continental drift
to be a fact, it was opposed by the
scientific world of his time due to the
fact that he couldn’t give a reason of
force that would move the
continents. Wegener died in 1930 and
never found a reason.
1.Seafloor Spreading
a.This is the evidence that Wegener was
searching for to prove his hypothesis
of continental drift.
b.This is the movement of the ocean
floor away from either side of a midocean ridge.
c. A mid-ocean ridge is a system of
undersea mountain ranges that wind
around the Earth.
d.The Mid-Atlantic Ridge is an
undersea mountain range with a steep,
marrow valley along its center.
d. Due to the spreading of the seafloor,
the relative age of the ocean floor is
very young compared to the age of
the continental rocks.
i.The oceanic rocks are no older than 175
million years, while the oldest
continental rock is about 4 billion years
old.
e. A man named Harry Hess hypothesized the
action of seafloor spreading.
i. According to Hess, if the seafloor is pulling
apart, then it would cause a break, or rift, in the
seafloor, which would cause an upwelling of
magma from the rift. The magma would
eventually solidify and be new seafloor.
ii.If the seafloor is spreading at rifts, then it
would be possible that the continents are
spreading along with it.
a.Paleomagnetism
i.The study of the record of the
Earth’s magnetism in rocks.
ii.Recall that the Earth generates a
magnetic field and creates two
poles, North and South with
opposite polarity.
iii.As magma solidifies to form rock,
the magnetic fields of iron-rich
minerals align with the Earth’s
magnetic field, similar to a
compass.
1.When the rock hardens, the orientation
of the minerals are permanent and
point north.
a.Paleomagnetism as Evidence
i.Scientists have discovered bands of
minerals that do not point North, as they
should.
ii.This discovery shows that the Earth’s
polarity has reversed itself numerous
times in history (North is South, and
South is North).
iii.They have also discovered that
these bands are similar on either
side of an ocean rift and are dated
during the same period of polarity.
1.Being able to date bands of minerals
by their polarity on either side of an
ocean rift is proof of sea floor
spreading.
2. Scientists have also discovered a
band on continental rock that
matches a band on the opposite
side of an ocean rift and is in the
ocean. This is further proof of
continental drift.