Final answer:
Fossils are the remains or imprints of organisms from previous geologic times, such as teeth, bones, shells, or impressions. They are formed under favorable conditions and are found in the earth.
Step-by-step explanation:
Fossils are the remains or imprints of organisms from previous geologic times. These are the preserved parts of plants or animals that have been found in the earth. Fossils can include teeth, bones, shells, or even impressions of the organism's original form. They are formed under certain favorable conditions such as volcanic ash, limestone, or mineralized groundwater. The fossil record, although very incomplete, is a crucial tool for paleontologists to understand the history of life on our planet.