5. Objectives:
1. Explain how the continents drift;
2. Cite evidences that support continental drift;
3. Explain how seafloor spreads;
4. Illustrate how seafloor spreads; and
5. Predict what could happen in the future as
the tectonic plates continue to move.
7. PLATE TECTONICS
THEORY
> 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.
8. Reasons why plates move:
❑ Earth’s plate move along
convection currents that
form in the mantle.
• ridge push
• slab pull
10. Ridge Push
This is a model of sea floor spreading at a divergent boundary called
a mid ocean ridge.
Ridge push is the result of gravitational forces acting on the young, raised oceanic lithosphere
around mid-ocean ridges, causing it to slide down the similarly raised but weaker
asthenosphere and push on lithospheric material farther from the ridges.
11. As the new seafloor is formed at the mid-ocean
ridge, the old seafloor farthest from the ridge is
destroyed at the subduction zone.
12.
13. The plates drift away from
each other, but they also collide
into each other. As they move,
they will encounter other
plates and end up diving
beneath them. Places
where plates collide are called
"subduction zones."
14.
15.
16.
17. Did you know that the Earth’s longest
mountain range is underwater and is
called the mid-ocean ridge?
32. Evidences of Continental Drift
Theory
1. The apparent fit of the continents
2. Fossil Correlation
3. Rock and Mountain Correlation
4. Paleoclimate Data/Past Climate Data
33. 1. The apparent fit of the continents
The Continental Jigsaw Puzzle
The coastlines of the
continents appear to fit
together like the pieces of
puzzle.
The apparent fit is even
better when submerged
coastlines are examined. In
this diagram, significant
overlap of the coastlines
occurs only in the shaded
areas because underwater
sediments are extensively
deposited.
34. 2. Fossil Correlation
Evidence from
Fossils
Fossils- are preserved
remains or traces of
organisms(plants and
animals) from the
remote past.
35. 3. Rock and Mountain Correlation
Evidence from Rocks
Rock formations in Africa line up with that in
South America as if it was a long mountain
range.
36. 4. Paleoclimate Data/Past Climate Data
Coal beds were formed from the
compaction and decomposition of swamp
plants that lived million years ago. These
were discovered in South America,
Africa, Indian subcontinent, Southeast
Asia, and even in Antarctica.
Glaciations were found in Africa, South
America, India and Australia
37.
38.
39. He could not find the force that was
causing the continents to drift.
Because of this, he could not
convince anyone that continents
could move.
He died in Greenland on an
expedition.
At the time of his death, no one
believed his hypothesis!
40.
41. ❑THIS CYCLE IS A QUASI-
PERIODIC AGGREGATION
AND DISPERSAL OF EARTH’S
CONTINENTAL CRUST.
❑ONE COMPLETE CYCLE IS
SAID TO TAKE 300-500
MILLIONYEARS.
42. Seafloor Spreading Model
Seafloor spreading is a continuous
process where tensional forces on both
sides of the plates caused them to
constantly move apart.
47. Seafloor spreading is also
pulling the continents of
Australia, South America,
and Antarctica away from
each other in the East
Pacific Rise.
48. The East Pacific Rise is
one of the most active
sites of seafloor
spreading , with more
than 14 centimeters
every year.
49.
50. Is the earth getting
larger and wider
when plates drift
away from each
other?
51. As the new seafloor is formed at the mid-ocean
ridge, the old seafloor farthest from the ridge is
destroyed at the subduction zone.
52. The rate of formation
of a new seafloor is
not always as fast as
the destruction of the
old seafloor at the
subduction zone.
53. What will happen to
the size of the ocean
when the seafloor
spreading is faster
than the subduction?
54. If subduction is faster than the seafloor spreading,
the ocean shrinks.When the seafloor spreading
is greater than the subduction, then the ocean
gets wider.
Answer:
This explains why the Pacific ocean is
getting smaller and why the Atlantic ocean
is getting wider.
