HOW THE WORLD WORKS (PART I) INSIDE THE EARTH AND PLATE TECTONICS

AGENDA Some History Continental Drift Plate Tectonics A Peek Inside

FACT OR FICTION? Think of something people used to believe that is no longer held to be true… Was it opinion or fact? What about now? Flat Earth Animal Machines Alchemy What changed? New evidence New ideas about existing evidence

Just don’t call me Alfie. Seriously. Don’t. “…we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw.” – Alfred Wegener

CONTINENTAL DRIFT? In 1912, meteorologist Alfred Wegener proposed that the continents were slowly moving. He theorized that: About all of Earth’s land masses had, at one point, drifted and collided to form supercontinent: Pangaea. And the supercontinent Pangaea broke up due to Continental Drift Though ridiculed, he was correct and this did take place approximately 200-300 million years ago! Alfie Wegener

WHY DID HE BELIEVE THIS? His primary evidence for continental drift included: The fit of the continents. (Why do you think?) Fossil evidence. Similarities between rock types. Evidence of glaciers in warm areas. (Why did these (2, 3, 4) matter?) (How might he have known?) Pangaea, ~300m B.C.E.

1. FIT OF THE CONTINENTS First, Wegener noticed that the continents are shaped such that they could fit together like puzzle pieces. E.g. eastern coast of South America and western coast of Africa.

1­. FIT OF THE CONTINENTS

2­. FOSSIL EVIDENCE Fossils of similar plants and animals were found on different continents, suggesting that at one point, they shared the same landmass. E.g. Glossopteris, a prehistoric (now extinct) plant in Antarctica, South America, and Africa, could not have spread seeds across the ocean!

2­. FOSSIL EVIDENCE

3. ROCK-TYPE SIMILARITIES Similar rock types (age and structure) were found along mountain ranges on different continents. E.g. the Caledonian Mountains in Scandinavia and Ireland, the Atlas Mountains in Northwestern Africa, and the Appalachians in Eastern North America.

4. GLACIAL EVIDENCE There is evidence of prehistoric ice sheets present in Africa, South America, India, Australia. Wegener theorized the only way this could happen was if continents had been located at higher (colder) latitudes at some point. e.g. glacial striations (scrapings) found in hot desert regions.

IN SUMMARY 300 million years ago, all Earth’s land formed the supercontinent: Pangaea. 200 million years ago, Pangaea breaks up due to Continental Drift. Wegener’s 4 proofs of his theory: Jigsaw fit between South America and Africa. Same fossils on each continent. Same mountains on both sides of Atlantic Ocean. Glaciers covered parts of several related continents.

Alfred Wegener’s theory of Continental Drift explained that the land on Earth developed through the steps outlined above.

MO’ MAGMA, MO’ PROBLEMS… Wegener’s peers did not share his enthusiasm for the theory of Continental Drift. They mocked and ridiculed him, because he could not explain how or why the continents moved. In other words, they would not believe him until he presented a cause (a force) that could reasonably and logically explain the movement of the continents. Poor Alfie. 

CANADA TO THE RESCUE! I am so smart. S-M-R-T! In 1968, John Tuzo Wilson, a Canadian geophysicist who studied Continental Drift discovered the “how” that had evaded Wegener. Wilson proposed that “convection currents” in the earth’s mantle (molten core) provided adequate energy to displace landmasses.

A QUICK PEEK INSIDE THE EARTH…

THE EARTH’S MANTLE The Earth’s mantle is a layer below the crust that descends to 2900 km below the surface. The upper part of the mantle is less dense than the crust above it, and the crust therefore “floats” on top of the mantle. The movement of the continents (tectonic plates) can be compared to broken slabs of ice floating on a lake in winter time.

MANTLE CONVECTION Convection is the transfer of heat though a material (e.g. water, magma, air). It creates cycles (or currents), with warmer areas rising and cooler areas falling. In the mantle, lower-lying magma is hotter and less dense, therefore it tends to rise. Magma located at higher points in the mantle is cooler and more dense, and therefore descends.

PLATE TECTONICS IS BORN! Earth’s outer shell is made up of 20 plates made of continental and oceanic crust. These float on a layer of hot rock, several kilometers below surface of the earth slowly churning. Earth’s core causes the convection currents that move the tectonic (continental or oceanic) plates. Fun Fact: Movement of Earth’s plates has shaped Canada’s mountains and helped to form fossil fuels.

MAJOR TECTONIC PLATES OF THE WORLD…

And now, a musical finish!  COMING UP NEXT… Journey to the Center of the Earth (ooh…) Tectonic Plate Movement (aah…) DISASTERS STRIKE! (eep!) And now, a musical finish!  https://www.youtube.com/watch?v=DGGlfb1UI-4