A geologist is someone who is involved in the study of the outer layer of the earth's crust. The objective of geology is to understand the history of the planet we live on; to better predict the future and to explain current occurrences of earthquakes, volcanic eruptions, and landslides.
A paleontologist, on the other hand, looks at the fossil remains of many types of organisms on the Earth's surface. Paleontology is the study of primitive life, including plant and animal organisms, fungi, bacteria, etc.