Chapter 8: Changes to Earth’s Surface Lesson 3: What are fossils?

Fossil- The remains or traces of a plant or animal that lived long ago. Fossil record- The information about Earth’s history that is contained in fossils. Fossils form in sedimentary rock. 1st- the organism dies and is covered in sediment. 2nd- the soft parts of the animal decay. 3rd- A space forms in the rock where the soft part used to be. 4th- Minerals fill the space. Lastly, as the sediment hardens, it preserves the fossils shape. Most fossils are formed from only the hard parts of living things, such as: shells, bones, and teeth. Trace fossils don’t tell how a whole plant or animal looked, but tells something about it. Example; a fossils footprint is trace fossil, tells about the animals size and how it moved. Fossils of animals droppings show what an animal ate.

The geologic time scale helps scientist understand better what was living during each part of this history. The four main eras of the geologic time scale from earliest to present are: Precambrian Time, Paleozoic Era, Mesozoic Era, and the Cenozoic Era Cenozoic Era is the present era, when humans first appeared. Mesozoic Era is the era when dinosaurs were dominant. Paleozoic Era is the era when the trilobites were dominant. Precambrian Time is when one-celled organisms were dominant and covers Earth’s early history.