PLATE TECTONIC
THEORY
QUARTER 1-LESSON 1

Have you ever wondered how the
land masses, the islands and
continents were formed?
Did they just exist the way they are
now or the results of a long
process and sequential events?

CRUST ( outermost layer )
- thickness ranges from 5 to 50 km. Thickest in a part
where a relatively young mountain is present and
thinnest along the ocean floor.
- Composed of several broken plates that move
continuously.

MANTLE
- Extends 2900 km from the Earth’s surface.
- Makes up about 80% of the Earth’s total volume
- Mostly made of the elements silicon, oxygen, iron and
magnesium
- The crust and upper part of the mantle is called the
lithosphere.
- ASTHENOSPHERE is located beneath the lithosphere
that is weak and soft layer made of hot molten
material.

CORE
- Subdivided in 2 layers; the inner and outer core
- Outer core is mainly made of iron and nickel moving
around the solid inner core. Its temperature reaches up
to 2000 C
- Inner core is made of solid iron and nickel. Its
temperature reaches to 5000 C but is believed to have
solidified due to pressure freezing.

WHAT IS PLATE TECTONICS?
- the entire lithosphere of the Earth is broken into numerous
segments called PLATES
- the plates move very slowly but constantly, this movement is called
TECTONICS
• Thus, the theory of moving lithospheric plates is called PLATE
TECTONICS.
WHY DO PLATES MOVE?
- plates move because of the properties and processes that occur in
the Earth’s Interior.
• Due to intense heat in the Earth’s interior, the molten rock (magma)
in the mantle moves in a cyclic pattern forming convection cells.

THE EARTH’S MECHANISM
1. PLATE TECTONIC THEORY
- ALFRED WEGENER , an German climatologist, first
noted the theory
- states that the Earth’s crust is composed of several
broken plates that continuously move either away, past or
towards each other.
2. THE CONTINENTAL DRIFT THEORY
- In 1912 , ALFRED WEGENER proposed a theory that
states
“ about 200 million years ago, the continents were once
one large landmass “
He called the landmass PANGAEA - a greek word which
means all earth.

PANGAEA broke into smaller continents called LAURASIA
and GONDWANALAND. These smaller continents broke
into the continents and drifted apart.
EVIDENCES OF CONTINENTAL DRIFT THEORY
A. The continental jigsaw puzzle
B. Evidence from Fossils
C. Evidence from Rocks
D. Coal Deposits

3. SEAFLOOR SPREADING THEORY
- supports the continental drift theory
- in the early 1960s HARRY HESS with ROBERT DIETZ
formulated the theory that states
“ hot less dense material from below the Earth’s crust
rises towards the surface at the mid-ocean ridge. This
material flows sideways carrying the seafloor away from
the ridge and creates a crack in the crust. The magma
flows out of the crack, cools down and becomes the new
seafloor”

Findings that support SEAFLOOR SPREADING
a.Rocks are younger at the mid-ocean ridge
b.Rocks far from the mid-ocean ridge are older
c.Sediments are thinner at the ridge
d.Rocks at the ocean floor are younger than those at the
continents