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Continental Drift https://www.youtube.com/watch?v=ELd3ebldSTs

Wegener’s Hypothesis

Warm Up

Research the earthquake from April 16, 2016 and write down 3 interesting things.

Evidence: coastline similarities ■

In the late 1500s, Abraham Ortelius, a Dutch mapmaker noticed the apparent fit of continents on either side of the Atlantic Ocean

Wegener ■

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1912, Alfred Wegener, German Scientist Proposed Continental Drift Hypothesis

Continental Drift Hypothesis ❑

Earth’s continents had once been a single landmass ■

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Named the landmass “Pangaea” (means “All Land”) Named the ocean surrounding Pangaea “Panthalassa” (means “All Seas”)

Panthalassa

Pangaea Breaks Apart ■

Wegener proposed that Pangaea began to break apart about 200 mya ■

The continents began to slowly move to their present positions

Evidence for Continental Drift ■

Evidence for Continental Drift can be found in 4 main areas: 1. 2. 3. 4.

Coastline similarities Similarities of plant & reptile fossils Ancient climatic evidence Geologic patterns of rocks & mountain chains

Evidence: fossil similarities ■

Similar fossils were found on widely separated continents Examples ❑ Glossopteris: plant that grew in temperate zones; fossils found in wide array of climatic zones today ❑ Kannemeyerid & Labyrinthodont: land-dwelling animals; could not have swam across oceans

Evidence: fossil similarities ■

Ages of these fossils predated Wegener’s time frame for break-up of Pangaea

Evidence: fossil similarities

Evidence: ancient climatic evidence ■

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Discovered similarities by studying sedimentary rocks Coal deposits have been found in Antarctica and Coal forms from dead swamp plants

Evidence: ancient climatic evidence ■ Glacial deposits found in Africa, India, Australia, and South America. Once these areas had once been covered by thick ice caps

Evidence: geologic patterns ■

Similar groups of rocks have been observed in the Appalachian Mountains of the United States, Greenland, and Europe ■

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These rock groups predate the breakup of Pangaea Support Wegener’s idea geologic structures (such as mountains) broke apart as the continents separated

Evidence: geologic patterns

Hypothesis Rejected ■

Most scientists rejected Wegener’s hypothesis because of 2 unanswered questions: 1. What forces could move the continents? 2. How can forces move without shattering?

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Wegener died in 1930, still searching for evidence to prove his hypothesis.

Where is evidence found? ■

1947, scientists begin mapping ocean floor ■

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Enabled by advancements in technology (mostly due to WWII)

Scientists used: ■ ■

Sonar Magnetometers – used to construct magnetic maps of the seafloor

Evidence from Sonar ■

Sonar revealed existence of: ■

Ocean Ridges ▪

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Undersea mountain ranges with steep, narrow valleys running down the center In the valley of the ridge is a break (or rift) in the earth’s crust where magma is pushed to the surface

Trenches ▪

Long, narrow depressions on sea floor

Evidence from Sonar ■

Studied Trenches & Ridges and found: ■ Age of rocks that make up seafloor vary and age consistently increases with distance from a ridge ■ Thickness of ocean-floor sediment increases with distance from ridge

Evidence from Magnometers ■

Paleomagnetism (study of Earth’s magnetic record) helped scientists determine the age of the ocean floor ■

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Molten rock containing iron becomes magnetic as it hardens (on an atomic level, becomes aligned with Earth’s magnetic pole) Earth’s magnetic pole reverses through geologic time Magnetic patterns of ocean floor were compared to magnetic patterns of land

Theory of Seafloor Spreading ■

States that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches

Magma is forced toward the crust along an ocean ridge and fills the gap that is created.

When the magma hardens, a small amount of ocean floor is added to Earth’s surface.

Theory of Seafloor Spreading ■

This theory was the missing link needed by Wegener to complete his model of continental drift.