Fossils: Clues to Earth Long Ago

Our Earth has been around for millions and millions of years. And for all that time, Earth has been changing. There were once tropical forests where there are now deserts, and oceans where there are now snowy mountains. Many animals that once roamed Earth are now extinct—they all died out long ago.

So how do we know what Earth was like millions of years ago? One way is by studying fossils—the remains of ancient plants and animals that have been turned into stone.

Fossils are like a diary of the past. And some of the most exciting stories they tell are about those amazing and mysterious creatures we call dinosaurs.

How did a dinosaur become a fossil? Usually when a dinosaur died, it rotted away and was lost forever. But sometimes a skeleton was covered with dirt and mud that preserved it. Very slowly, the bones absorbed minerals from the mud. They turned into stone, and became fossils that scientists can study today.

Fossil Facts

Sometimes scientists find fossils of sea creatures, such as the trilobite, high in the mountains. Could the land where it was found once have been under the ocean?

Millions of years ago, some insects got trapped in gooey tree sap that hardened into a kind of fossil called amber. The amber preserves the bugs exactly as they were when they were alive.

Dinosaur fossils are the largest fossils ever discovered. Scientists hardly ever find a complete dinosaur skeleton. Fossilized dinosaur eggs have been found all over the world. Footprints can tell us a lot about dinosaurs—how big they were, how fast or slowly they moved, where they roamed, and whether they traveled alone or in herds.

Scientists never find dinosaur skin (it rotted away long ago), but fossil imprints can show what dinosaur skin was like.


  1. What has happened to the bones of some dinosaurs' that were buried under dirt and mud?
    Answer: The bones of some dinosaurs that were buried under dirt and mud have turned to stone, or fossilized.
  2. Why is this change important for scientists studying dinosaurs?
    Answer: Fossilization is important because it saves the dinosaurs bones so that they can be studied today. If this change did not happen, we would not know about dinosaurs.
  3. What do scientists learn from fossils?
    Answer: Answers will vary but could include that scientists learn about the kinds of animals that used to live on Earth. Scientists learn how, long ago, these animals lived and what these animals ate.
  4. Which dinosaur is your favorite dinosaur? Why?
    Answer: Answers will vary.