Earth's Layers — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. What produces Earth's magnetic field?
A) The spinning of solid rock inside the mantle.
B) The rotation of tectonic plates on the surface.
C) The movement of liquid iron and nickel flowing in the outer core.
D) The extreme heat of the solid inner core radiating outward.
Earth's magnetic field is generated by swirling currents of liquid iron and nickel in the outer core, which act like a giant electric dynamo.
2. A compass needle always points toward magnetic north. Which layer of Earth is responsible for this?
A) The crust, because it contains magnetic rocks on the surface.
B) The mantle, because its convection currents pull the needle.
C) The outer core, because its flowing liquid metal creates a magnetic field around the planet.
D) The inner core, because solid iron is naturally magnetic.
A compass works because the flowing liquid metal in the outer core produces a magnetic field that extends to Earth's surface and into space, pulling the needle toward magnetic north.
3. Mars does not have a global magnetic field today. Based on what you know about Earth, what does this suggest about Mars?
A) Mars never had any iron inside it.
B) Mars likely does not have a flowing liquid metal core like Earth does.
C) Mars is too close to the Sun for a magnetic field to form.
D) Mars has too many volcanoes, which block the magnetic field.
Since Earth's magnetic field comes from its flowing liquid outer core, the absence of a magnetic field on Mars suggests Mars's core has cooled and solidified, stopping the dynamo effect.
4. Scientists discover that ancient lava flows on the ocean floor show reversed magnetic patterns. What does this evidence tell us?
A) The lava flows came from different volcanoes on opposite sides of the ocean.
B) Earth's magnetic field has flipped direction many times throughout its history.
C) The ocean floor was once above water and faced the opposite direction.
D) The outer core stops moving for short periods and then restarts.
When lava cools, its iron minerals lock in the direction of Earth's magnetic field at that time. Alternating magnetic stripes in seafloor rock prove the field has reversed direction many times over millions of years.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Earth's magnetic field extends far into space and forms a protective shield called the magnetosphere.
The magnetosphere is a huge invisible shield created by Earth's magnetic field that deflects harmful solar wind and radiation, protecting life on the surface.
2. The colorful aurora borealis, or northern lights, occurs when solar particles interact with Earth's magnetic field.
The aurora borealis happens when charged particles from the Sun are funneled by Earth's magnetic field toward the poles, where they collide with gas molecules and produce colorful light displays.
3. The outer core is about 2,200 kilometers thick and made of liquid iron and nickel.
The outer core stays liquid because its temperature is high enough to melt iron and nickel, and the pressure at that depth is not great enough to force the metal into a solid state.
4. Without its magnetic field, Earth's atmosphere would be stripped away by solar wind over time.
The magnetic field acts as a shield that blocks solar wind from blasting away air molecules. Without it, Earth's atmosphere would slowly erode into space, much like what happened on Mars.
5. A compass is a tool that uses Earth's magnetic field to show which direction is north.
A compass contains a magnetized needle that freely spins and aligns with Earth's magnetic field lines, always pointing toward magnetic north so travelers can find direction.