Presentation on theme: "The Restless Continents v=uGcDed4xVD4&feature=relate d&safety_mode=true&persist_sa fety_mode=1."— Presentation transcript:
The Restless Continents http://www.youtube.com/watch? v=uGcDed4xVD4&feature=relate d&safety_mode=true&persist_sa fety_mode=1
Have you ever looked at a map of the world? O Did you notice how the coastlines of continents on opposite sides of the oceans appear to fit together like the pieces of a puzzle?
Is this a coincidence? O How is it that the coastlines fit together so well? O Is it possible that the continents were actually together sometime in the past?
Wegener’s Continental Drift Hypothesis O One Scientist who looked at the pieces of this puzzle was Alfred Wegener in the early 1900’s O He wrote about his hypothesis: Continental Drift
Continental Drift O The hypothesis that the continents once formed a single landmass, broke up, and drifted to their present locations.
Continental Drift explained a few puzzling questions O Why do the continents seem to fit together like a giant puzzle? O Why are fossils of the same plant and animal species found on continents that are on different sides of the Atlantic Ocean? O Mesosaurus – SA, Africa O Glossopterous –Antartica, Africa, Australia O Why are rocks with different magnetic alignments found in the same place (paleomagnetism)?
The Hypothesis O Wegener made many observations before proposing his hypothesis of continental drift. O He thought that all the present continents were once joined in a single, huge continent called Pangaea
Pangaea O “Pangaea” means “all earth” O It existed about 245 million years ago O It split into two huge continents about 180 million years ago O Laurasia O Gondwana O These two continents split again about 65 million years ago to form the continents we know today
But Wegener’s theory of continental drift was not widely accepted during his lifetime…. O Many scientists would not accept his hypothesis. O They said that the calculated strength of the rocks that make up the Earth’s crust would not allow the crust to move in that way. O Many years later, other evidences were presented that supported his theory.
What do you think… O Our continents will look like in the future? O Will we move back together? O Will we be further apart? O What evidence will future scientists use to show our current day locations?
Demonstration of Sea Floor Spreading O Fold your 1 meter of paper in half to form a “V” O Slide the paper between two tables. Have them close enough to grip the paper, but far enough apart so that the paper can slide through the crack. O Using the ruler, slide the paper out 10 cm one each side. O Draw a vertical line on the paper at the table’s crack. Label this area “1” on both sides of the paper O Measure out 10 more cm, draw your line and label this area “2”on both sides of the paper O Continue this until you have 5 sections on each side
The Restless Planet: Sea Floor Spreading Unit 2: Sixth Grade
So what did Wegener believe was moving the continents? O Sea-floor Spreading ! O It was proposed that as the tectonic plates move apart, it creates a rift that allows magma to rise to the surface of the ocean floor and solidifies. O Mid-Ocean ridges are places where sea-floor spreading takes place O Mid-Atlantic Ridge O This creates new crust in that area, further pushing the continents apart. O Evidence: older crust is farther away from the mid-ocean ridge than newer crust is.
Debate O We will be debating the most compelling evidence to support the theory of continental drift. O There will be three groups. O Group 1: Fossil Similarities O Group 2: Landform Similarities O Group 3: Sea Floor Spreading O You will have 20 minutes to form your argument. O Use notes, ITs, netbooks to find info O Write your points on the construction paper as bullets O Groups will then present their arguments to the class
Other evidence to support continental drift O Stratigraphy: studying the layers of the Earth, showed that the geologic columns in Antarctica and India were similar O Glaciation: Glacial deposits in Canada were also found in India and southern Africa O Marine Corals O Mountain Belts: ancient mountains in South Africa and near Buenos Aires, Argentina align when the two continents are fitted together.
More evidence to support Sea- Floor Spreading O Magnetic Reversals O Throughout Earth’s history, the north and south poles have changed places many times. O The molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals. O They act as compasses, lining up with the magnetic field of the Earth. O When the magma cools, these tiny compasses are preserved in the rock. O When the poles reverse, the mineral grains are aligned in with the “incorrect” pole. O Paleomagetism