Journey to the Earth’s Interior Children’s Ideas About Earth’s Interior

Children’s Ideas About Earth’s Interior

Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science (see the Session 1 Children’s Ideas Bibliography). Consider what evidence might refute this idea, and why a child would be likely to believe this?

1. Earth has a hot, molten rock core.

Earth has a solid metal inner core, and a liquid metal outer core. Temperatures in the inner core are near 6,000¾ C, while outer core temperatures are about 3500 ¾C. Children have probably been exposed to popular media where “journeys to the center of the Earth” portray dramatic rises in temperature and molten rock.

2. Earth is mostly molten, aside from a thin crust.

Scientific knowledge of Earth’s interior structure originates in the information interpreted from seismic waves, which behave differently as they pass through different materials in the interior layers of the Earth. This data has revealed that the Earth is made of four main layers: crust, mantle, outer core, and inner core. Children’s images of volcanoes erupting red-hot lava may lead to their thinking that the interior of the Earth consists of molten rock. This, along with their experience being limited to Earth’s surface, may cause them to reason that there are only two layers.

3. Children often think the Earth’s crust is thicker than it actually is, and are unaware of the correct proportions of each of the Earth’s layers.

At its most thick, the crust is about 40km (25 miles) deep. This is a thin layer when compared to the other layers of the Earth. The mantle is the thickest layer at about 2,885 km (1,790 miles), followed by the outer core at 2,270 km (1,400 miles), and then the inner core, which has a diameter of about 1,216 km (755 miles). Since children’s common experience is limited to the Earth’s crust, its size is often exaggerated in their thinking.

4. There is a magnet at the Earth’s center.

Children have heard about the Earth’s magnetic field and because of their experiences with magnets commonly think that there is a giant magnet at Earth’s center, and that this core causes Earth’s magnetic field. The Earth does act like a giant bar magnet, with its “ends” being the magnetic North and South poles. Both the inner and outer core are made of metal — mostly iron — which has magnetic properties. Current science theory suggests that convection currents in the outer core may be responsible for the Earth’s magnetic field.

5. Some children think there are hollow spaces inside of the Earth, while others think that it uniformly solid.

Each of the Earth’s layers, though different chemically and physically, is continuous with no gaps or cavities. Children’s understanding of Earth’s interior is not based on any experiences they might have. Their perception of the ‘unseen’ can resort to a simple, uniform model of the Earth. Images of lakes, rivers, and caverns deep inside of the Earth are perpetuated by popular fictional media, which may account for the hollow Earth model held by some children.

6. The mantle is a liquid or at least partially liquid.

The Earth’s mantle is actually quite complicated in its structure. The upper mantle is solid at the top, with a layer that is believed to be partly molten (liquid) beneath it. The lower mantle is made up by solid rock that is under conditions of extreme heat and pressure. Children may have been taught about the physical state of the layers of the Earth, including the mantle, and this property of acting both like a liquid and a solid is likely to be confusing.