A paleontologist studies the history of life on Earth through the examination of fossils, which are the remains or traces of ancient organisms. They analyze these fossils to understand the evolution, behavior, and ecology of past life forms, as well as the environments in which they lived. Paleontologists often work in the field to excavate fossil sites and in laboratories for research and analysis, contributing valuable insights into the planet's biological history. Their work helps to clarify the connections between extinct species and modern organisms.