Science: Plate Tectonics Worksheet

Question 1

Define plate tectonics in your own words.

Accepted Answer

Plate tectonics is the scientific theory that Earth's outer shell is broken into large moving plates that interact and change the surface over time.

Question 2

Name the three main types of plate boundaries and describe the motion at each one.

Accepted Answer

The three main types of plate boundaries are divergent, convergent, and transform. At divergent boundaries, plates move apart. At convergent boundaries, plates move toward each other. At transform boundaries, plates slide past one another.

Question 3

Explain how seafloor spreading provides evidence for plate tectonics.

Accepted Answer

Seafloor spreading provides evidence for plate tectonics because new oceanic crust forms at mid-ocean ridges and moves outward on both sides. This shows that plates are moving and that the ocean floor is not fixed.

Question 4

What is convection in Earth's mantle, and how does it help move tectonic plates?

Accepted Answer

Convection in Earth's mantle is the slow movement of hot material rising and cooler material sinking. This transfer of heat helps drive plate motion by dragging or pushing the lithospheric plates above.

Question 5

Describe what typically happens when two oceanic plates converge.

Accepted Answer

When two oceanic plates converge, one plate usually subducts beneath the other. This can form a deep-ocean trench and a chain of volcanic islands called an island arc.

Question 6

Describe what typically happens when an oceanic plate converges with a continental plate.

Accepted Answer

When an oceanic plate converges with a continental plate, the denser oceanic plate usually subducts beneath the continental plate. This can produce a trench, earthquakes, and volcanic mountains along the edge of the continent.

Question 7

Describe what typically happens when two continental plates converge.

Accepted Answer

When two continental plates converge, neither plate easily subducts because both are relatively buoyant. Instead, the crust compresses, folds, and uplifts to form large mountain ranges.

Question 8

Why are earthquakes common near plate boundaries?

Accepted Answer

Earthquakes are common near plate boundaries because plates interact there and stress builds up as they collide, pull apart, or slide past one another. When the stress is released suddenly, the ground shakes.

Question 9

Explain why many volcanoes are found around the edges of the Pacific Ocean.

Accepted Answer

Many volcanoes are found around the edges of the Pacific Ocean because several plate boundaries there involve subduction. As oceanic plates sink, rock melts and magma rises, forming volcanoes in the region known as the Ring of Fire.

Question 10

What is a transform boundary, and what landform or geologic activity is most commonly associated with it?

Accepted Answer

A transform boundary is a place where two tectonic plates slide past each other horizontally. It is most commonly associated with faults and frequent earthquakes.

Question 11

Compare oceanic crust and continental crust in terms of thickness, density, and typical age.

Accepted Answer

Oceanic crust is thinner, denser, and generally younger than continental crust. Continental crust is thicker, less dense, and often much older.

Question 12

How do magnetic stripes on the seafloor support the idea that plates move?

Accepted Answer

Magnetic stripes on the seafloor show symmetrical patterns of normal and reversed polarity on both sides of mid-ocean ridges. This pattern indicates that new crust formed at the ridge and moved outward over time, supporting plate motion.

Question 13

A scientist finds a deep ocean trench next to a volcanic mountain chain along a continent. What type of plate boundary is most likely present, and why?

Accepted Answer

The most likely boundary is a convergent boundary between an oceanic plate and a continental plate. This is because subduction of the oceanic plate can create both a deep trench and a volcanic mountain chain on the continent.

Question 14

How can GPS measurements provide evidence that tectonic plates are moving today?

Accepted Answer

GPS measurements can detect very small changes in the positions of points on Earth's surface over time. These measurements show that continents and other crustal regions move a few centimeters each year, which is direct evidence of plate motion.

Question 15

Explain how plate tectonics helps scientists understand the past and predict future geologic activity.

Accepted Answer

Plate tectonics helps scientists understand where continents and oceans were in the past by reconstructing plate movements. It also helps them identify regions that are more likely to experience earthquakes, volcanic eruptions, and mountain building in the future.

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Science: Plate Tectonics

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