Paleontology is the study of ancient life, older than 10,000 years. The word "paleontology" is derived from three Greek words: "palaios," meaning ancient; "onto," meaning being; and "logy," meaning study of.
There are five main subdivisions of paleontology:
1. Invertebrate paleontology = study of animals with no backbone (e.g., sponges, corals, snails, clams, ammonites, trilobites).
2. Vertebrate paleontology = study of animals with a backbone (e.g., fish, dinosaurs, horses, elephants, humans).
3. Paleobotany = study of land plants.
4. Micropaleontology = study of microscopic organisms and microscopic parts of large organisms; palynology = study of pollen and spores, could be included in this subdivision.
5. Ichnology = study of tracks, trails, burrows, boreholes, tooth marks, and artifacts.
In recent years, a new subdivision, called Exopaleontology has been emerging. It deals with the evaluation of the possibility of finding evidence of ancient life on other planets. Examples of such life include blue-green bacteria (which construct cabbage-head-like structures called stromatolites); cold-desert soil bacteria; and hot-vent organisms. Some of these types of organisms can live in extremely harsh environments (very cold or very hot).