Earth's Layers — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. If Earth's outer core suddenly became solid, what would most likely happen?
A) Volcanoes would erupt more frequently around the world.
B) Earth would lose its magnetic field, leaving us unprotected from solar radiation.
C) The mantle would stop flowing and earthquakes would increase.
D) The inner core would melt because pressure would decrease.
Earth's magnetic field is generated by liquid iron circulation in the outer core. If it solidified, the magnetic field would disappear.
2. A volcano erupts on an island in the Pacific Ocean. Which layers of Earth are most directly involved in this event?
A) Only the crust, because lava flows on the surface.
B) The crust and mantle, because magma rises from the mantle through cracks in the crust.
C) The outer core and inner core, because they produce the heat.
D) All four layers equally, because heat travels evenly through Earth.
Volcanic magma originates in the mantle, then rises through fractures in the crust to erupt at the surface.
3. Why do scientists say that Earth's layers act like a system where each part affects the others?
A) Because all four layers are made of the same material.
B) Because heat from the core drives mantle convection, which moves crustal plates, causing surface events.
C) Because earthquakes happen in every layer at the same time.
D) Because the crust controls the temperature of all deeper layers.
Core heat → mantle convection → plate movement → earthquakes and volcanoes at the surface. All layers are interconnected.
4. Two cities are the same distance from an earthquake. City A is on solid granite bedrock and City B is on soft sediment. Which city likely felt stronger shaking and why?
A) City A, because granite carries seismic waves faster and with more energy.
B) City B, because soft sediment amplifies seismic waves and shakes more.
C) Both cities felt the same shaking because distance is the only factor.
D) City A, because granite is heavier and vibrates more during earthquakes.
Soft sediment amplifies seismic wave energy and can liquefy, causing much more damage than solid bedrock.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Without Earth's magnetic field, harmful radiation from the Sun would reach the surface.
Solar wind and cosmic radiation are deflected by the magnetosphere. Without it, life on Earth's surface would be at risk.
2. The Hawaiian Islands were formed by a hot plume of magma rising from deep in the mantle.
A mantle plume is a column of hot rock rising from deep in the mantle, creating volcanic hotspots like Hawaii.
3. Scientists believe Earth's magnetic poles have reversed many times throughout history.
Paleomagnetic evidence in ocean floor rocks shows that Earth's magnetic north and south poles have switched many times.
4. Tectonic plates move only a few centimeters per year, about as fast as fingernails grow.
Plates move 1-10 cm per year on average — slow in human terms but enough to create mountains over millions of years.
5. Geologists study fossils to learn about past events recorded in Earth's rock layers.
Fossils embedded in rock strata record the history of life and Earth's changing conditions over time.