• I will examine the evidence for the theory of plate tectonics

• Draw and explain the 3 types of plate boundaries and what is likely to occur at these boundaries

Evidence Supporting Evidence Supporting Continental DriftContinental Drift

Continental Drift TheoryContinental Drift Theory

• Proposed by Alfred Wegener in 1912

• 250 million years ago, all of the continents were combined into one super-continent called “Pangaea”

• The continents gradually drifted apart to where they are today

Alfred Wegener (1880-1930),Alfred Wegener (1880-1930),

German meteorologist and geologist, was the first person to propose the theory of continental drift.

In his book, "Origin of Continents and Oceans," he calculated that 200 million years ago the continents were originally joined together, forming a large supercontinent. He named this supercontinent Pangaea, meaning "All-earth".

Evidence to Support the TheoryEvidence to Support the Theory

Exhibit OneExhibit One

The Shapes Match The continents look as if they were pieces

of a giant jigsaw puzzle that could fit together to make one giant super-continent.

The bulge of Africa fits the shape of the coast of North America while Brazil fits along the coast of Africa beneath the bulge.

““Puzzle Pieces”Puzzle Pieces”

• Continents look like they could be part of a giant jigsaw puzzle

Pangaea Interactive Map GameClick on the link above and Click on the link above and

complete gamecomplete game

Exhibit one Exhibit one

http://www.ucmp.berkeley.edu/geology/anim1.html

From Present to 750M years ago

From 750m years ago to Present

http://www.ucmp.berkeley.edu/geology/anim4.html

Exhibit TwoExhibit Two

• The Plants and Animals Match Wegener noted that plant fossils of late Paleozoic age found on several different continents were quite similar.

• This suggests that they evolved together on a single large land mass. He was intrigued by the occurrences of plant and animal fossils found on the matching coastlines of South America and Africa, which are now widely separated by the Atlantic Ocean.

• He reasoned that it was physically impossible for most of these organisms to have traveled or have been transported across the vast ocean. To him, the presence of identical fossil species along the coastal parts of Africa and South America was the most compelling evidence that the two continents were once joined

• Put the puzzle pieces together and discover for yourself

land reptile

Permian ferns

land reptile

freshwater reptile

Madagascar

Mesosaurus, a freshwater reptile, could not have been able to swim across the Ocean,

and no evidence of land bridges.

Untold tragedies of Continental Drift. .

Exhibit ThreeExhibit Three

• The Rocks Match Broad belts of rocks in Africa and South America are the same type. These broad belts then match when the end of the continents are joined.

Matching of mountain ranges Matching of mountain ranges on different continentson different continents

Sequence of RocksSequence of Rocks

• Same rock patterns found in South America, India, Africa, Antarctica and Australia

Exhibit FourExhibit Four

• The Ice Matches • Wegener was aware that a continental ice sheet

covered parts of South America, southern Africa, India, and southern Australia about 300 million years ago.

• Glacial striations on rocks show that glaciers moved from Africa toward the Atlantic Ocean and from the Atlantic Ocean onto South America. Such glaciations is most likely if the Atlantic Ocean were missing and the continents joined.

Pangaea with S. Africa centered over the South Pole accounts for glacial ice in the southern continents.

Regions with areas with extensive coal deposits from the same time period would have been near the Equator.

Exhibit FiveExhibit Five

• The Positions Don't Match If the continents were cold enough so that ice covered the southern continents, why is no evidence found for ice in the northern continents? Simple! The present northern continents were at the equator at 300 million years ago.

• The discovery of fossils of tropical plants (in the form of coal deposits) in Antarctica led to the conclusion that this frozen land previously must have been situated closer to the equator, in a more temperate climate where lush, swampy vegetation could grow.

Glaciers movement

Now cooler climate regions used to be at the Equator

Exhibit 6 Evidence still happeningExhibit 6 Evidence still happening• Sea-floor spreading is the process in

which the ocean floor is extended when two plates move apart.  As the plates move apart, the rocks break and form a crack between the plates. 

• Earthquakes occur along the plate boundary.  Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.

As magma piles up along the crack, a long chain of mountains forms gradually on the ocean floor.  This chain is called an oceanic ridge

Notice the location of the old and Notice the location of the old and new rocknew rock

• Essentials of Geology : Chapter 2 : Animations

Exhibit 6 Sea –Floor SpreadingExhibit 6 Sea –Floor Spreading

ConclusionConclusion

• Based on the evidence presented come up with a conclusion. Which piece of evidence do you feel is the most important? Why?