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Science C8 L3

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dan lin

on 25 April 2016

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Transcript of Science C8 L3

Evidence for a New Theory
Though Wegner had evidence that supported his theory
of continental drift, no one believed him. People of the time
mostly thought Wegner was CRAZY.

The problem with Wegner's theory was that he could not
explain why or how the continents drifted apart.
After Wegner passed away, advances in technology allowed scientists to form new discoveries about the ocean floor, and in turn, new evidence supporting Wegner's theory.
New discoveries about the ocean floor:

Not flat
Contains deep trenches
Has huge mountain range that runs through the middle of the oceans (mid-ocean ridge)
The ridge is where the ocean
is splitting apart. Magma rises at the ridge to form a new crust and expand the sea floor.

By viewing the sea floor, scientists discovered some surprising evidence in support of Wegener's theory.
Scientist Harry Hess speculated that the sea floor at the mid-ocean is increasing in size as new crust is formed, and he called this process sea-floor spreading

The age of the rocks that make up the ocean floor gets older as you move away from the ridges at the center. This meant that the youngest rocks were found near the ridges, and the oldest rocks near the continents.
As the Earth is not increasing in size, Hess concluded that the
Atlantic Ocean is expanding and the Pacific Ocean is shrinking.
Magnetic Reversals

Since its existence, Earth's magnetic field has reversed several times.
This fact further supports that the Earth's sea floor is in fact expanding.


The ocean floor consists of the magnetic mineral, known as magnetite. As magnetite in molten magma cools, it lines up like a magnet and its north ends point to Earth's North Pole, whereas its south end points to Earth's South Pole.

When Earth's magnetic field is reversed, the new magma and crust being formed will have magnetite pointing in the opposite direction.

Technological advancements also allowed scientists to survey earthquake and volcanic
activity under water as well as on land.

With these new observations, and the previous observations made from Wegner, a new theory known as
plate tectonics
was developed.

Plate Tectonics
The New Theory

According to this theory, the Earth's surface is covered by about a dozen large plates that are continually moving.
These plates are made up of:
Continental crust
Oceanic crust
Or both
Based on the theory of plate tectonics, why was Wegner's theory of continental drift incorrect?
Though there has been significant technological advancements since Wegner's time period, scientist are still researching what makes the plates move.
Read pages 226-229
Questions 1-4

What hypothesis did German Scientist Alfred Wegner come up with about the Earth's continents?
Sea-Floor Spreading
The idea of earth’s continents once occurring as a single land mass struck Wegener while he was examining fossil distribution patterns of certain ferns and animals. He noticed that the fossils were present on either sides of the earth, reasoned out by geologists of the time as being the result of land bridges,allowing organisms to occupy distant continents. This did not sit well with Wegener. He then noticed the distinctive correlation between the coastlines of Africa and South America which led him to believe they must have at one point been joined. He further postulated that all the continents were initially a single super-continent, Pangea.

The unconventional nature of the theory was initially ridiculed however as people declined to accept its claims. Wegener set out to find more substantial evidence of his assertions but had no suitable suggestions as to what might be driving the continents to move. The trends arising from his vast body of data derived from various disciplines, however, were difficult to ignore and led researchers to look more deeply into his claims.
What will our world be like in the next 250 million years? Have a look at the image from NASA of PangeaUltima, the next proposed super-continent.
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