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:
Temperature decreases as you travel deeper into Earth's interior.
Corrected: Temperature increases as you travel deeper into Earth's interior.
The corrected sentence is: "Temperature increases as you travel deeper into Earth's interior." The error was opposite direction — temperature rises with depth, not falls: the original sentence "Temperature decreases as you travel deeper into Earth's interior." needed to be fixed.
2. Fix the sentence:
The mantle is about 300 kilometers thick and is Earth's thinnest layer.
Corrected: The mantle is about 2,900 kilometers thick and is Earth's thickest layer.
The corrected sentence is: "The mantle is about 2,900 kilometers thick and is Earth's thickest layer." The error was wrong measurement and rank — mantle is the thickest layer at 2,900 km: the original sentence "The mantle is about 300 kilometers thick and is Earth's thinnest layer." needed to be fixed.
3. Fix the sentence:
Tectonic plates float on top of the outer core and move very quickly.
Corrected: Tectonic plates float on top of the upper mantle and move very slowly.
The corrected sentence is: "Tectonic plates float on top of the upper mantle and move very slowly." The error was wrong layer and speed — plates rest on the mantle and move only centimeters per year: the original sentence "Tectonic plates float on top of the outer core and move very quickly." needed to be fixed.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Heat from Earth's core causes rock in the mantle to flow in slow circles called convection currents.
Convection currents form because hot rock near the core rises while cooler rock sinks, creating slow circular movements that drive plate motion.
2. The deeper you go inside Earth, the greater the pressure pushing on the rock around you.
Pressure builds with depth because all the rock and material above pushes down with increasing weight, squeezing everything below it.
3. The crust beneath the ocean is made of a dense rock called basalt.
Basalt is a dark, dense volcanic rock that forms when magma cools quickly on the ocean floor, making it the main rock type in oceanic crust.
4. When two tectonic plates push into each other, they can build tall mountains.
When plates collide, the crust crumples and folds upward over millions of years, building mountain ranges like the Himalayas.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Why does the inner core stay solid even though it is hotter than the outer core?
Sample answer: The inner core stays solid because the pressure at Earth's center is so enormous that it squeezes the iron and nickel tightly together, preventing them from melting even at extreme temperatures.
A good answer includes: The inner core stays solid because the pressure at Earth's center is so enormous that it squeezes the iron and nickel tightly together, preventing them from melting even at extreme temperatures.
2. What are convection currents, and how do they affect the crust?
Sample answer: Convection currents are slow circular movements of hot rock in the mantle. They push tectonic plates on the surface, which can cause earthquakes and volcanic eruptions at plate boundaries.
A good answer includes: Convection currents are slow circular movements of hot rock in the mantle. They push tectonic plates on the surface, which can cause earthquakes and volcanic eruptions at plate boundaries.