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Warm Up• 1. What is the thickest layer of the Earth? • 2. What is the thinnest layer of the Earth?• 3. What happens to temperature as the
depth within the Earth increases? • 4. What happens to the density as the
depth within the Earth increases? • 5. When you put your marshmallow into
the candle flame, what type of heat transfer were you modeling?
It makes sense right?
• We know the Asthenosphere is a “plastic solid” or a solid that can move and flow….just like Jell-O!
• So why does it sound so crazy?
Alfred Wegener (Vegner) got the same response for his theory.
http://education-portal.com/academy/lesson/alfred-wegeners-theory-of-continental-drift.html#lesson
https://www.youtube.com/watch?v=MEh4B1Pv8YE
Wegener’s Theory of Continental Drift:
• What is Continental Drift?
It is the idea or Theory ……..that the continents slowly
move over Earth’s surface.
• All continents had once been joined together in a single land mass (PANGAEA) and later began to drift apart.
• Wegener was not alone in thinking that the continents appeared to fit together like puzzle pieces.
• He, however, came up with a theory to suggest that the continents were once joined together and drifted apart.
Sit very still!
• Can you feel the North American plate moving?
• It was a pretty radical idea at Wegener’s time to say the continents were moving.
• Most scientists were skeptical.
• However, Wegener had evidence…..
Wegener’s 3 main pieces of evidence:1. Landforms- Shapes of the Continents – They appeared to ‘fit’ South America and Africa.
Coal Fields - In North America and Europe match up when pieced together (also ‘fit’ as well)
Mountains and Rock Layers – In North America and Europe match up when the continents are pieced together (similar rocks)
2. Fossil Evidence - Fossils of the same animals were found on many different continents, now separated by oceans:
Glossopteris = plant
Cynognathus = land reptile
Lystrosaurus = land reptile
Mesosaurus = freshwater
reptile
These organisms had no way to travel across such oceans that exists today!
Wegener’s 3 main pieces of evidence:
• Also, fossils of the Glossopteris (a fern) have been found in rocks of Africa, South America, Australia, India, and Antarctica!
• Finding these fossils on such widely separated landmasses, convinced Wegener that the continents had once been united.
3. Climate Evidence – Tropical Plants - Found in areas that are considered Arctic (frozen) today.
Glaciers - Evidence of glaciers found in areas that have temperatures far too mild to have glaciers.
Evidence shows that climate must have been much different in the past
Wegener’s 3 main pieces of evidence:
So why didn’t Wegener’s fellow scientists accept his theory?
• He was missing one key point to support his theory?
• Can you guess what evidence the other scientists wanted to hear?
They wanted to know ….. HOW continental drift happened?
• Wegener could not provide an explanation for the force that pushes or pulls the continents.
Case closed, not enough evidence!
• Most scientists believed that the Earth was cooling and shrinking, which created Earth’s mountain ranges. (like the dried up, wrinkled skin of an apple)
• Wegener said that if this was true, Mountains should be found all over Earth, but they usually occur in bands along the edges of continents.
• Unfortunately, Wegener died before his theory was ever accepted.
• He went on a Meteorological expedition to Greenland one winter, and got lost in a bad snow storm.
continental drift animation link
http://www.phschool.com/webcodes10/index.cfm?wcprefix=cfp&wcsuffix=1015&fuseaction=home.gotoWebCode&x=0&y=0
https://www.youtube.com/watch?v=JmC-vjQGSNM
Sea-Floor Spreading