Plate Tectonics ppt wb

Continental Drift

The Story …

https://www.youtube.com/watch?v=AtDAOxaJ4Ms
magnetic field clip

As accurate maps were

developed,

■ people noticed the

continents fit
together like
puzzle pieces.

■ Alfred Wegener

(1912) proposed
that the continents
were joined
together in the
past and broke
apart about 200
million years ago.

The large landmass was called

■ PANGAEA (all the Earth)

■ Continental drift states that continents

have moved horizontally to their current
locations.

■ Wegener and other scientists didn’t have

enough evidence so this idea was
REJECTED.

Pangaea

Evidence for Continental Drift

Early Evidence

■ Fossil and

climate clues:
fossils like
Mesosaurus
(reptile) and
Glossopteris
(fern) were
found on
different
continents

Fossils of warm weather plants indicate

similar climate on continents

where they were found.

Rock Clues: similar rock structures were

found on different continents.

■ ex. Coal fields, glacier deposits, folded

mts that matched

We find similar rock
types on continents
on opposite sides of

the Atlantic

Ocean.

Similar, age, structure

and rock types are

found in the

Appalachian Mtns.

(N.A.) and mountains

in Scotland and

Scandinavia.

More evidence
Sea floor spreading and Harry Hess
(1960’s):

■ He suggested that

mid-ocean ridges
were formed when
hot, less dense
material in the mantle
is forced upward
and carries the
seafloor away from
the ridge.

■ SO????

This is called RIDGE PUSH andGravity Pull

Age Evidence: Rocks in the seafloor are much

younger than on the continents and the youngest rocks

are at the mid-ocean ridges.

■ This diagram shows the

Americas being
separated from the
Europe and Africa as
the seafloor spreads.
Continents are grey in
color. Youngest
seafloor is redand as
seafloor gets older it
becomesyellow, green
and then blue.

Age of oceanic crust; youngest (red) is along spreading

centers.

The outercorecreates a magnetic field and

periodically (over millions of years) reverses polarity.

For example all rocks that form from cooling magma will be

magnetized with north pole (magnetic north).

Magnetic
Clues:
Paleomagnetism

When the magnetic field REVERSES, rocks would crystallize and have a
magnetism that lines up with the South Pole (magnetic south)

Earth's magnetic field
periodically reverses polarity
— the north and south poles
switch. Rocks crystallizing
during one of these periods of
magnetic reversal will be
magnetized with a polarity
opposite of rocks the
crystallize today

Magnetic Clues:
Paleomagnetism

■ Rocks in ocean show

many magnetic
reversals proving that
new rock was being
formed at mid-ocean
ridges.

■ *Ocean floors are

changing too.

http://www.youtube.com/watch?v=WhiF6IqGACo Video on
paleomagentism!

As new
seafloor is
created at the
ridge, it is
added in
equal amounts
to both edges
of the
spreading
seafloor. We
see the
pattern of
stripes as
mirror images
on both
sides of the
ridge —
strongest
evidence for
seafloor
spreading.

In the Pacific, the stripes are much wider — indicating a faster rate of spreading (or creation of
new seafloor). In the Atlantic, the stripes are much more narrow — indicating relatively slow
rate of spreading.

Continental Drift Ad

■ An advertisement is something used to get

people to buy a product or believe in something.

■ Use page 444-445 and pick 1 piece of evidence

that you want to advertise.

■ Make it colorful and include a picture!

■ Your choices

■ Rock formations, fossil evidence, ancient

climate clues