Plate tectonics: Evidence of plate movement | Cosmology & Astronomy | Khan Academy

Summary

This video explores the evidence supporting the theory of tectonic plate movement. It starts by noting the shape of continents, like South America and Africa, suggesting they were once connected. Key discoveries follow, including the mid-Atlantic ridge and magnetic rock alignment in the ocean floor, revealing shifts in Earth’s magnetic field. The video then discusses how rock formations near the ridge support the theory that plates are moving apart. Finally, GPS technology is introduced to measure plate movements, offering conclusive evidence of slow but continuous tectonic activity. The video concludes by hinting at further exploration of why the plates move.

Takeaways

• 😀 The appearance of continents fitting together, like South America and Africa, suggests they were once connected.
• 😀 The discovery of underwater mountain ridges, such as the mid-Atlantic ridge, hints at tectonic plate movement.
• 😀 Volcanic activity along the ocean ridges supports the idea that plates are moving apart, with lava contributing to new ocean floor formation.
• 😀 Magnetic rocks, which align with Earth's magnetic field when they harden, show evidence of the fluctuating magnetic field over time.
• 😀 Magnetic rock alignment patterns reveal that Earth's magnetic poles have flipped, further supporting plate movement.
• 😀 The striped pattern of magnetic rock on either side of the mid-Atlantic ridge suggests the ocean floor was once together and has since moved apart.
• 😀 The symmetry of magnetic stripes on opposite sides of the ridge indicates that the continents were once connected and have since diverged.
• 😀 The shifting of magnetic rock over time supports the theory that tectonic plates are continuously moving and spreading.
• 😀 Geological evidence from the 1960s showed that the plates are moving apart, with new rock being formed at the mid-ocean ridges.
• 😀 Modern GPS technology confirms the movement of tectonic plates, with some plates shifting at rates of about 1 cm per year, which adds up over millions of years.

Q & A

What is the first clue suggesting that the lithospheric plates are moving relative to each other?

The first clue is the observation that the continents seem to fit together, such as how the coastlines of South America and Africa align. This suggests that at some point, these continents may have been connected before moving apart.

How do underwater ridges support the theory of plate tectonics?

The discovery of a ridge in the middle of the Atlantic Ocean, along with volcanic activity and lava flow, indicates that new material is being added to the ocean floor. This suggests that the lithospheric plates are moving apart at these ridges.

What role does the magnetic alignment of rock play in understanding plate movement?

The magnetic rock that forms at the ocean floor aligns with Earth's magnetic field as it cools. By studying the magnetic orientation of these rocks, geologists discovered that the magnetic field has reversed over time, providing evidence that the ocean floor has been created and moved symmetrically away from mid-ocean ridges.

Why is the alternating magnetic orientation of rocks significant?

The alternating magnetic orientation of rocks on either side of the mid-Atlantic ridge shows that the ocean floor has been created over time by volcanic activity. The symmetric patterns of magnetic stripes suggest that the plates have moved apart, with new material forming at the ridge.

What does the term 'magnetic striping' refer to in the context of plate tectonics?

Magnetic striping refers to the pattern of alternating magnetic orientations found in the ocean floor rocks. These stripes are symmetrically arranged on either side of mid-ocean ridges, supporting the idea that new crust is constantly being formed and that the plates are moving apart.

How does the discovery of Earth's fluctuating magnetic field support the idea of plate tectonics?

The discovery that Earth's magnetic field has reversed over time provides evidence that the ocean floor formed in distinct stages. The symmetrical magnetic stripes on either side of mid-ocean ridges suggest that the plates are moving apart, with the ocean floor being created in sync with the magnetic reversals.

What is the speed at which tectonic plates are moving?

Tectonic plates move at a slow rate, roughly the speed at which fingernails grow—around a centimeter per year. This gradual movement can result in large shifts over millions of years.

What tools are used to measure the movement of tectonic plates today?

GPS satellites are used to accurately measure the movement of tectonic plates. This technology allows scientists to track the movement of plates, such as the Pacific Plate moving northwest near Hawaii.

How do the magnetic stripes help in determining the age and movement of ocean floor rocks?

The magnetic stripes reveal the timing of the formation of oceanic crust. By measuring the distance from the ridge and the orientation of the magnetic rocks, scientists can estimate the age of the rocks and understand how the plates have moved apart over time.

Why is the mid-Atlantic ridge important in the study of plate tectonics?

The mid-Atlantic ridge is a critical area for studying plate tectonics because it is an active divergent boundary where tectonic plates are moving apart. It is here that new oceanic crust is formed through volcanic activity, and the magnetic stripes in the ocean floor provide evidence of past plate movements.