Fossils are defined as the preserved remains of a past geological age. After a living organism died, it (or evidence of its activity) became buried under the ground in the layers of sediment. Once these layers become rock, the remains are said to be fossilized. Most fossils are of extinct organisms.
1. Hard tissues such as shells, teeth and bones are more likely to become fossils, because softer materials usually decomposed before they became fossilized. Today we have the bones of huge dinosaurs that once walked the earth and the shells of giant, nautilus-like creatures called ammonites that once swam in the seas. 2. Fossils can also be the remains of activities of an organism--these are called trace fossils, and include such things as coprolites (fossilized feces), footprints and burrows. Coprolites are especially valuable, since they can tell us what a creature ate, and footprints and burrows tell us how far it moved and where it lived.
3. The oldest fossil known is of a blue-green algae that lived on some rocks in South Africa 3.2 billion years ago. 4. Fossil facts are always being updated. It used to be that the oldest dinosaur known was the Eoraptor, which was 228 million years old and lived in Argentina. But a recent find in Madagascar is even older: a Prosauropod from 230 million years ago.
5. The biggest dinosaur fossil is Sauroposeidon, which is believed to have stood 60 feet tall and may have weighed as much as 60 tons. That's as tall as a six-story building and as heavy as a nine elephants. 6. The smallest fossils of all are the one-celled organisms that are also the oldest: the blue-green algae. The tiniest dinosaur fossil was found recently in China. Microraptor was the size of a crow (about 12 inches long).
7. About 65 million years ago, at the division between the Cretaceous and the Tertiary periods (the K-T boundary), many species all went extinct at the same time, which we know by examining the fossil record. The most widely accepted explanation is that an asteroid hit the earth, causing many of the plants and animals that lived then to perish in a blaze of fire. The boundary can be seen with the human eye in the rock strata as a layer of iridium: this is a radioactive substance that is not found on earth but is found in asteroids. 8. Immediately after the K-T boundary event, we begin to see more and more fossils of mammals. It is thought that the rise of mammals wouldn't have happened if the dinosaurs, who were voracious predators, hadn't died out.
9. Fossil fuel does not come from dinosaurs, as many people believe. Rather, it comes from the fossilized remains of tiny organisms called diatoms. Because it took millions of years to make these fossils, this resource for fuel is non-renewable. 10. Fossilized diatoms are also used as abrasives and, in fact many of our toothpaste formulas use them to make the paste abrasive enough to clean our teeth.