Fossils - the remains and traces of organisms that lived long ago

• found mostly in sedimentary rocks
• formed slowly over hundreds of years

Mold fossils- a hollowed space in the shape of the organism

Cast fossils – minerals that have hardened into the shape of the original organism

True form fossils – actual remains in fossilized form

Trace fossils – evidence of creatures that lived long ago such as footprints, dung, etc.

The history of the earth has been divided into four major time intervals called eras. These eras have been broken down further into shorter time intervals called periods.

Precambrian – first and longest geologic time interval, few fossils have been found to give clues about this era. Most life consisted of algae and bacteria. Later in the period invertebrates such as jellyfish appeared.

Paleozoic – "ancient life" era, Pangaea forms, early in this era invertebrate life such as trilobites are found in the fossil record, later fish, insects, amphibians and the beginnings of reptiles emerge as well as mosses and ferns.

Mesozoic – "middle life" era, Pangaea separates into continents, this era is dominated by the dinosaurs, also known as the Age of the Dinosaurs. Small mammals and bird begin to emerge.

Cenozoic – "recent life" era beginning 65 million years ago when the dinosaurs disappeared, marked by the Ice Age, mammoths, and the gradual appearance of mammals, birds, and other animals recognizable today. Humans are seen here as well as flowering plants, forests, and grasslands.