Introduction to plate tectonics | Middle school Earth and space science | Khan Academy

TL;DR

The Earth's lithosphere is composed of tectonic plates that slowly move over time, shaping the continents and creating geological features like mountains and rift valleys.

Transcript

• [Narrator] What if I told you that the earth below you is moving? You'd probably say, "Of course it's moving. We're standing on a planet that's spinning on its axis while revolving around the Sun at about 107,000 kilometers per hour. And on top of that, our whole solar system is circling the center of the Milky Way galaxy." But there's another ki... Read More

Key Insights

• 🍽️ The Earth's lithosphere is composed of tectonic plates that slowly move on the asthenosphere.
• 🚵 The movement of tectonic plates shaped the continents and created geological features like mountains and rift valleys.
• 🍽️ Matching coastlines and similar fossils on different continents support the theory of plate tectonics.
• ☠️ Tectonic plates move at a slow rate of a few centimeters per year.
• 🍽️ Convergent plate boundaries occur when two plates collide, leading to the formation of mountains and volcanic activity.
• 🖕 Divergent boundaries happen when two plates move apart and create rift valleys and mid-ocean ridges.
• 🥺 Transform boundaries occur when plates slide past each other, leading to earthquakes.

Questions & Answers

Q: How fast do tectonic plates typically move?

Tectonic plates move only a few centimeters per year, about the same rate as the growth of fingernails. However, over millions of years, these small movements add up and lead to significant changes in the Earth's surface.

Q: How do scientists know that tectonic plates move?

Scientists have gathered evidence from geological features, such as complementary coastlines and similar fossils found on different continents. These observations support the theory of plate tectonics.

Q: What are convergent plate boundaries?

Convergent plate boundaries are places where two tectonic plates come together. The denser plate usually sinks beneath the other, leading to the formation of mountains or volcanic activity.

Q: What causes tectonic plates to move?

While internal heat may play a small role, gravity is the major driving force behind plate movement. The denser and cooler plates rest on top of the hotter asthenosphere, and gravity causes the edges of the plates to sink into the asthenosphere at convergent boundaries.

Summary & Key Takeaways

• The Earth's lithosphere is divided into tectonic plates that sit on top of the asthenosphere, and these plates slowly move over millions of years.

• The movement of these tectonic plates has led to the breakup of a supercontinent called Pangea and the formation of the continents we see today.

• Matching coastlines and fossil similarities across continents provide evidence for plate tectonics.