The document summarizes theories of continental drift and plate tectonics. In 1915, Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core. Wegener hypothesized that around 200 million years ago, all the continents were joined together in a supercontinent called Pangaea. Pangaea later broke apart into smaller supercontinents, and by the end of the Cretaceous period the continents had separated into their modern positions. In the 1960s, Harry Hess proposed the theory of seafloor spreading, which provided support for continental drift by showing how ocean floors spread outward from underwater ridges. Plate tectonics expanded on these ideas

1. Theories of
the Earth’s
Crustal
Movement

3. CONTINENTAL DRIFTCONTINENTAL DRIFT
THEORYTHEORY

4. In 1915, the German geologist and
meteorologist Alfred Wegener first
proposed the theory of continental drift,
which states that parts of the Earth's crust
slowly drift atop a liquid core. The fossil
record supports and gives credence to the
theories of continental drift and plate
tectonics.

5. Wegener hypothesized that there was a giganticWegener hypothesized that there was a gigantic
supercontinent 200 million years ago, which he namedsupercontinent 200 million years ago, which he named
PangaeaPangaea, meaning "All-earth"., meaning "All-earth".

6. Pangaea started to break up into two smaller supercontinents, called Laurasia andPangaea started to break up into two smaller supercontinents, called Laurasia and
Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, theGondwanaland, during the Jurassic period. By the end of the Cretaceous period, the
continents were separating into land masses that look like our modern-daycontinents were separating into land masses that look like our modern-day
continents.continents.

9. seafloor spreading, theory of lithosphericseafloor spreading, theory of lithospheric
evolution that holds that the ocean floors areevolution that holds that the ocean floors are
spreading outward from vast underwaterspreading outward from vast underwater
ridges. First proposed in the early 1960s byridges. First proposed in the early 1960s by
the American geologist Harry H. Hess, itsthe American geologist Harry H. Hess, its
major tenets gave great support to the theorymajor tenets gave great support to the theory
ofof continental driftcontinental drift geological theory that thegeological theory that the
relative positions of the continents on therelative positions of the continents on the
earth's surface have changed considerablyearth's surface have changed considerably
through geologic timethrough geologic time ..

13. Plate tectonics is the theory that the outer rigid layer of thePlate tectonics is the theory that the outer rigid layer of the
earth (theearth (the lithospherelithosphere) is divided into a couple of dozen) is divided into a couple of dozen
"plates" that move around across the earth's surface relative to"plates" that move around across the earth's surface relative to
each other, like slabs of ice on a lake.each other, like slabs of ice on a lake.

14. Brainstorming Activity:Brainstorming Activity:
Of the three theoriesOf the three theories
presented, which onepresented, which one
convinced you most?convinced you most?

15. THANK YOU AND HAVE A GOOD DAY!
By: Beth G. Labrador
Jimalalud National High School
Jimalalud, Negros Oriental