Target What is continental drift?

Continental Drift The theory that continents can drift apart from one another and has done so in the past.

Here is a map of the continents today. What do you notice about these “pieces”?

Alfred Wegener “Doesn't the east coast of South America fit exactly against the west coast of Africa, as if they had once been joined?"

Alfred Wegener and the theory of Continental Drift

Who was Wegener? Wegener was a German born meteorologist. Proposed his theory of Continental Drift in 1912.

What does Wegener’s theory say? Wegener determined that all the separate continents today were once joined in a single land mass he called PANGEA. Over millions of years, Pangea broke apart and drifted away.

Pangea 180 million years ago 250 million years ago

What proof did Wegener have? Fossils of the same plant and animal species are found on both sides of the Atlantic. example: Fossils of Mesosaurus, a small aquatic reptile, and Glossopteris, an ancient plant species, have been found on several continents.

What other proof did Wegener have? Glaciers cut grooves into the ground as they move. When you bring all the continents back to their original arrangement, the glacial grooves match up!

Is there more proof? Rock sequences in South America, Africa, India, Antarctica, and Australia show similarities.

The rock layers

This is great in theory, but can you PROVE it? Wegener’s theory of Continental Drift was not accepted by many scientists. Can you guess why scientists rejected his theory?

Rejected…Why? What force in nature could move entire continents? In Wegener’s day, no one knew “why” or “how” continents move.

What happened next? Before anyone could answer why or how continents can move, Wegener died during a winter expedition in Greenland. He was 50 years old.

So, why did the continents move? Sea- Floor spreading Occurs when the crust on the ocean floor pulls apart, and magma comes through this gap to form a newer layer of crust. The Mid-Atlantic Ridge are places where sea- floor spreading takes place.

How do we know sea-floor spreading occurs? Magnetic reversal- when Earth’s magnetic poles change place. The molten rock (magma) at the mid-ocean ridges contains tiny grains of magnetic minerals. These mineral grains act like a compass, as they align with the magnetic field of the Earth. When molten material cools, the record of these tiny compasses is really set in stone!

Do you think the continents are drifting today? Yes