Earth's Layers — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Earthquakes happen when tectonic plates stay perfectly still for a long time.
Corrected: Earthquakes happen when tectonic plates suddenly shift and release stored energy.
The corrected sentence is: "Earthquakes happen when tectonic plates suddenly shift and release stored energy." The error was opposite cause — earthquakes result from plate movement, not stillness: the original sentence "Earthquakes happen when tectonic plates stay perfectly still for a long time." needed to be fixed.
2. Fix the sentence:
Volcanoes form in the middle of tectonic plates and never appear near plate edges.
Corrected: Volcanoes most often form near plate boundaries where magma can rise through cracks in the crust.
The corrected sentence is: "Volcanoes most often form near plate boundaries where magma can rise through cracks in the crust." The error was wrong location — most volcanoes occur at plate boundaries: the original sentence "Volcanoes form in the middle of tectonic plates and never appear near plate edges." needed to be fixed.
3. Fix the sentence:
The crust is one single unbroken piece of rock that covers the entire planet.
Corrected: The crust is broken into many large pieces called tectonic plates that fit together like a puzzle.
The corrected sentence is: "The crust is broken into many large pieces called tectonic plates that fit together like a puzzle." The error was incorrect description — the crust is divided into multiple tectonic plates: the original sentence "The crust is one single unbroken piece of rock that covers the entire planet." needed to be fixed.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Melted rock beneath Earth's surface is called magma, but once it erupts it is called lava.
Magma is melted rock trapped underground, and scientists use a different name -- lava -- only after it reaches the surface through a volcanic eruption.
2. The Ring of Fire is a zone around the Pacific Ocean where many earthquakes and volcanoes occur.
The Ring of Fire circles the Pacific Ocean because this basin is surrounded by converging and subducting plate boundaries, making it Earth's most volcanically active zone.
3. A fault is a crack in the crust where blocks of rock have moved past each other.
A fault is a fracture in Earth's crust created by tectonic stress, where blocks of rock shift position and can trigger earthquakes when they suddenly slip.
4. When plates pull apart, hot mantle rock can rise up and create new ocean floor.
At divergent boundaries, plates separate and magma rises to fill the gap, cooling into new oceanic crust on the seafloor.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. How does the mantle cause tectonic plates on the surface to move?
Sample answer: Hot rock deep in the mantle rises toward the surface while cooler rock sinks, creating slow convection currents. These currents push and drag the tectonic plates, causing them to move a few centimeters each year.
A good answer includes: Hot rock deep in the mantle rises toward the surface while cooler rock sinks, creating slow convection currents. These currents push and drag the tectonic plates, causing them to move a few centimeters each year.
2. Why do most earthquakes and volcanoes happen along the Ring of Fire?
Sample answer: The Ring of Fire has many plate boundaries where tectonic plates collide, pull apart, or slide past each other. This constant plate interaction causes frequent earthquakes and allows magma to reach the surface as volcanoes.
A good answer includes: The Ring of Fire has many plate boundaries where tectonic plates collide, pull apart, or slide past each other. This constant plate interaction causes frequent earthquakes and allows magma to reach the surface as volcanoes.