Tectonic Plates

Question 1

Scientists studying a canyon observe three pieces of evidence: (1) sediment layers that are each about 10,000 years old, (2) a V‑shaped valley at the top of the canyon, and (3) large, rounded boulders that have been polished by moving water. Which explanation best describes how geologic processes have changed the canyon’s surface over both long time scales and short time scales?

Accepted Answer

Over millions of years, the river slowly downcut the canyon, creating the V‑shaped valley, and during recent storms the river’s fast flow moves and polishes the boulders.

Answer

Over millions of years, repeated volcanic eruptions built the canyon, and in the past few hundred years human digging deepened it.

Answer

Over millions of years, tectonic uplift raised the land, and in the past few thousand years wind erosion carved the V‑shaped valley.

Answer

Over millions of years, glaciers carved the canyon, and in the past few decades earthquakes have widened it.

Question 2

Scientists describe the Earth's crust as being broken into huge pieces that behave in three ways: they are large plates, they float on hotter, softer rock beneath, and they move only a few centimeters each year. Which statement correctly includes all three ideas?

Accepted Answer

The crust is divided into several giant plates that rest on a softer, hotter layer beneath and slide only a few centimeters each year.

Answer

The crust consists of separate tiles that are glued together and never move.

Answer

The crust is made of many tiny rock blocks that float on a liquid ocean inside the Earth and drift rapidly.

Answer

The crust is a single solid shell that stretches like a rubber band and snaps, moving quickly when it breaks.

Question 3

Which statement best explains why Earth's tectonic plates are able to move?

Accepted Answer

The plates float on a layer of hot, partially melted rock called the mantle, which behaves like a very slow‑moving liquid, allowing the plates to drift.

Answer

The plates rest on a solid, unmoving layer of rock, so they slide like a book on a table.

Answer

Magnetic forces from the core pull the plates around the Earth.

Answer

The plates are glued to the mantle, but earthquakes make them jump from place to place.

Try three questions

Scientists describe the Earth's crust as being broken into huge pieces that behave in three ways: they are large plates, they float on hotter, softer rock beneath, and they move only a few centimeters each year. Which statement correctly includes all three ideas?

Which statement best explains why Earth's tectonic plates are able to move?

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