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Evidence of the Wegener’s Continental Drift Hypothesis and The Theory of Plate Tectonics
The Theory of Plate Tectonics:
1. The Earth’s lithosphere is divided into tectonic plates that drift on the asthenosphere
2. The plates move by convection currents that either push the plates together, apart or make them
slide past each other.
Evidence 1: (This is a summary of the Pangea lab we did!)
In the early 1900’s Alfred Wegener wrote about his hypothesis of continental drift. Continental
drift is the hypothesis that states the continents were once formed in a single landmass and then
“drifted” apart to there present locations. Some pieces of evidence Wegener used to support his
hypothesis are 1) through his observations, the continents seem to fit together. 2) Plant and animal
fossils of the same species found on both sides of the ocean. 3) Similar types of rocks can be found on
different continents. 4) The same ancient climatic conditions were found on several continents. 5)
Glacial marks of the same glacier found on different continents.
What does this say/prove about our continents?
Which part of the theory of plate tectonics does it support? How does it support it? Explain.
Even though Wegener had so much evidence to support his hypothesis, scientists around the world
rejected it. Why do you suppose the hypothesis was rejected? (Look again at his evidence vs. the
theory!)
Evidence 2: PART A
Scientists did not support Wegener’s hypothesis of continental drift because he could not
explain how the continents moved. After World War II, seismometers were installed to monitor nuclear
testing. These seismometers showed a distinct pattern in the location of earthquakes and volcanoes
around the world. Through the use of seismometers, in the 1960’s Harry Hess discovered that the seafloor was spreading at mid-ocean ridges. Sea-floor spreading is the process where as the sea-floor
spreads apart, magma rises up through the sea-floor, fills in the gaps and solidifies making new ocean
floors. Proof of sea-floor spreading is that younger rocks are found near the mid-ocean ridge, and older
rocks are found further away from the mid-ocean ridge. Other proof for this is also the measurements
of Africa and Asia moving apart from each other at a rate of 1.6 cm per year. As the sea floor grows, the
continents move further apart.
Which part of the theory of plate tectonics does this support? How does it support it? Use data from
above to explain.
Evidence 2: PART B
Another important discovery was the mid-ocean ridges themselves. This is the location where
sea-floor spreading takes place and where sea-floor spreading is monitored.
Mid-ocean ridge
map
Explain what happens at mid-ocean ridges. (Hint: See part A)
How does this support the Theory of Plate Tectonics?
Evidence 3:
Throughout Earth’s history, the Earth has changed its polarity many times, meaning magnetic
north and south is reversed. The molten rock at the mid-ocean ridges contains tiny grains of magnetic
minerals. The mineral grains contain iron and are like compasses. Magnetic reversals are recorded in
the sea-floor as it spreads. (Hint: Compare the 2 pictures! Also look at the polarity!)
How does this support the Theory of Plate Tectonics?
How do both graphs above relate to each other?