| A | B |
|---|
| Geologic Time | divided by events, not specific lengths of time, all the length of time from the formation of earth. |
| eon | longest subdivision in the geologic time scale that is based on the abundance of certain types of fossils and is subdivided into eras, periods, and epochs. |
| era | the second largest division of geologic time Cenozoic-current era |
| period | the third largest division of geologic time-Quaternary-current period, humans from around 500,000 years ago, dominant form of life from about 10,000 years ago. |
| epoch | smallest division of geologic time, is characterized by differences in life-forms that may vary regionally. |
| organic evolution | change of organisms over geologic time. |
| species | group of organisms that reproduces only with other members of their own group. |
| natural selection | process by which organisms that are suited to a particular environment are better able to survive and reproduce than organisms that are not. |
| trilobite | oragnism with a three-lobed exoskeleton that was abundant in Paleozoic oceans and is considered to be an index fossil. |
| Pangaea | large, ancient landmass that was composed of all the continents joined together. |
| life | state of being in which one grows, reproduces, and maintains, a constant internal environment. |
| Precambrian time | is the longest part of Earth's history and includes Hadean, Archean, and Proterozoic Eons. |
| cyanobacteria | are blue-green algae thought to be one of the earliest forms of life on Earth. |
| Paleozoic Era | an era of ancient life, began about 544 million years ago and ended about 245 million years ago. |
| dinosaur | a reptile from one of two orders that dominated the Mesozoic Era |
| Mesozoic Era | or era of middle life, was a time of many changes on Earth. |
| Cenozoic Era | or era of recent life, began about 65 million years ago and continues today. |
| foliated | metamorphic rocks with layered mineral grains |
| nonfoliated | metamorphic rocks with nonlayered mieral grains |
