So how can we know things about Earth from the time before there were people The answers lay in the discovery and study of fossils Fossils represent time lots and lots of time They are snapshots that we can look at to learn about prehistoric life that existed an incredibly long time ago Some fossils are the remains of ancient plants or animals Some fossils are of plants or animals that still exist today
While Earth's exact age is impossible to know with certainty scientific dating methods used on rocks show the Earth to be about four and a half billion years old By contrast the fossils of modern humans date back merely thousands of years That leaves billions of prehistoric years with no human witnesses It's difficult to understand just how much time that is The noted scientist and fossil expert Stephen Jay Gould once said that if the timeline of life's history on Earth were represented by a person's arm the part of the arm occupied by human beings would amount to no more than a single fingernail clipping The rest of the finger hand and arm all the way back to the shoulder would Stephen Jay Gould represent prehistory Almost all of what we know about prehistoric life comes from fossils
CHAPTER TWO Fossil Formation Bodies of Evidence Traces of Ancient Life A fossil is a hardened imprint stamp or cast of an actual organism that was once alive on Earth The forces and events that form fossils can take millions of years to unfold Ammonite Because of the accidental nature of fossil formation the chances of any living thing becoming a fossil are slim
There are two main kinds of fossils Scientists refer to these two types as body fossils and trace fossils Body fossils are stone imprints molds or casts left by the Trilobite remains of actual organisms that were once living These include animals plants and people Sometimes they are just a part of the organism such as teeth or a single bone Other times they can include an entire skeleton Trace fossils on the other hand are fossilized indicators of life but not the actual organism itself Trace fossils include footprints tracks eggs burrows and even fossilized excrement left behind by prehistoric creatures EXAMPLES OF BODY FOSSILS EXAMPLES OF TRACE FOSSILS Trilobite Trace fossils like footprints can tell scientists a great deal about the size of the creature that left them and even how fast the animal could move Lambeosaurus Mammoth Femur Megalodon Tooth Fossilized dinosaur eggs
