Earth Science: Plate Tectonics and Continental Drift
Exploring how Earth's plates move and shape the planet
Earth Science: Plate Tectonics and Continental Drift
Exploring how Earth's plates move and shape the planet
Earth Science - Grade 6-8
- 1
Alfred Wegener proposed that the continents were once joined together in one large landmass. What was this supercontinent called, and what idea did Wegener use it to support?
The name means all Earth or all lands.
The supercontinent was called Pangaea. Wegener used Pangaea to support the idea of continental drift, which says that continents have moved slowly over Earth's surface over time. - 2
List two pieces of evidence that supported Wegener's theory of continental drift.
Two pieces of evidence were the matching shapes of continents, such as South America and Africa, and matching fossils found on continents that are now far apart. Similar rock layers and signs of past climates also supported his idea. - 3
Explain why many scientists did not accept Wegener's idea of continental drift when he first proposed it.
Think about what part of his explanation was missing.
Many scientists did not accept Wegener's idea because he could not explain what force was strong enough to move entire continents. Later evidence about seafloor spreading and plate tectonics helped explain how continents move. - 4
What is a tectonic plate?
A tectonic plate is a large, rigid piece of Earth's lithosphere that moves slowly over the softer asthenosphere below it. Tectonic plates can include oceanic crust, continental crust, or both. - 5
Describe what happens at a divergent plate boundary.
The word divergent is related to moving apart.
At a divergent plate boundary, two plates move away from each other. Magma rises to fill the gap, cools, and forms new crust, which often happens at mid-ocean ridges. - 6
Describe what happens at a convergent plate boundary when an oceanic plate collides with a continental plate.
The denser plate is usually forced downward.
When an oceanic plate collides with a continental plate, the denser oceanic plate usually sinks beneath the continental plate in a process called subduction. This can create deep ocean trenches, volcanoes, and earthquakes. - 7
Describe what happens at a transform plate boundary.
At a transform plate boundary, two plates slide past each other horizontally. This movement can build up stress and cause earthquakes when the rocks suddenly break or slip. - 8
A scientist finds the same fossil species in rock layers in eastern South America and western Africa. Explain why this supports continental drift.
Think about whether the organism could travel across the Atlantic Ocean.
This supports continental drift because the same species would have had an easier time living in connected areas than crossing a wide ocean. The fossils suggest that South America and Africa were once joined together. - 9
Mid-ocean ridges are long underwater mountain chains where new oceanic crust forms. What plate boundary type is found at a mid-ocean ridge, and what process creates new crust there?
A mid-ocean ridge forms at a divergent plate boundary. New crust is created by seafloor spreading, when magma rises, cools, and hardens as the plates move apart. - 10
The oceanic crust is youngest near a mid-ocean ridge and gets older farther away from the ridge. Explain why this age pattern occurs.
Imagine a conveyor belt moving rock away from the center.
This pattern occurs because new oceanic crust forms at the ridge and then moves away on both sides as seafloor spreading continues. Crust farther from the ridge has had more time to move away, so it is older. - 11
What is subduction, and why does it usually involve oceanic crust sinking beneath another plate?
Density helps determine which plate sinks.
Subduction is the process in which one tectonic plate sinks beneath another plate into the mantle. Oceanic crust usually sinks because it is denser than continental crust. - 12
Explain how the Himalaya Mountains formed from plate movement.
The Himalaya Mountains formed when the Indian Plate collided with the Eurasian Plate. Because both plates carry continental crust, neither plate subducted easily, so the crust crumpled and uplifted into a mountain range. - 13
Earthquakes and volcanoes often form in patterns along plate boundaries. Why do these events happen more often near plate boundaries than in the middle of plates?
Focus on where plates interact most strongly.
Earthquakes and volcanoes happen more often near plate boundaries because plates interact there by colliding, separating, or sliding past each other. These interactions create stress, melting, and movement that can cause earthquakes and volcanic activity. - 14
Compare continental crust and oceanic crust. Include one difference in thickness and one difference in density.
Continental crust is generally thicker and less dense than oceanic crust. Oceanic crust is generally thinner and denser, which is why it often subducts beneath continental crust at convergent boundaries. - 15
A new island volcano is forming above a subduction zone near the edge of an oceanic plate. Explain the plate tectonic process that could create this volcano.
Subduction can create magma that rises to the surface.
The volcano could form where one oceanic plate subducts beneath another plate. As the sinking plate moves into the mantle, water and heat help rock melt, and magma rises through the crust to build a volcanic island.