Science

I wish I could build a time machine. I want to go to the future and see how my town has changed. I want to go to the past and see what Earth looked like a really long time ago.

I told my teacher about my idea. He liked it, but he said I don’t need a time machine to visit the past. He told me to study rocks. Rocks hold clues about what Earth was like long ago.

A sedimentary rock is like a history lesson. Long ago, sediment piled up in layers. Sediment is tiny bits of rocks and minerals. It can also contain parts of once-living things. As more and more layers piled up, the bottom layers were pressed together. The pressed-together sediment hardened. It formed sedimentary rock. Limestone and sandstone are sedimentary rocks.

Most limestone formed from the remains of ocean animals and plants that pile up on the ocean floor. How do you think sandstone formed? You guessed it! It formed from sandy sediment.

When I look at rocks, I imagine watching them form. I see sediment. I see layers form. I see the layers pressing together and hardening. In my mind, this takes only minutes. But in nature, the process takes a very long time.

Questions:

1. What is sediment?

2. What is needed for sediment to form rock?

3. How do limestone and sandstone compare?