What did early geologists believe about the Earth's composition?

• A. The earth was made up of water
• B. The earth was made up of rock
• C. The earth was hollow
• D. The earth was made up of metals

Answer: (B)

Early geologists built their understanding from what they could observe directly: solid rock. They studied rock types, how rocks form, and the way landscapes are built from rock layers. This focus on visible material led them to conclude that the Earth's outer parts are made up of rock. The idea of a hollow Earth isn’t supported by that same body of observations, and although metals exist inside the planet, the rocks they could study and name—the things they could map and classify—were the main evidence they used. So, describing the Earth as made up of rock best matches what early geologists concluded from their field observations.