| A | B |
|---|
| geologic time scale | record of earth's history |
| era | largest sub-division of the geologic time scale |
| epoch | sub-division of a period |
| period | sub-division of an era |
| organic evolution | gradual change in life-forms over time |
| species | group of plants or animals that normally breed only among themselves |
| natural selection | process by which organisms survive and evolve while others die out |
| endangered | describes a species with a small number of individuals that is in danger of dying out |
| habitat | any place where organisms live, grow, and interact with themselves and the environment |
| Precambrian time | oldest and longest division of geological time |
| cyanobacteria | blue-green bacteria; first and oldest life-form on earth |
| Paleozoic Era | second oldest division of geological time; began 544 million years ago |
| amphibian | vertebrate animals which must return to water to reproduce |
| reptile | scaly skinned vertebrate animals with hard-shelled eggs |
| Mesozoic Era | middle era of earth's history; began 245 mya when dinosaurs were dominant life form |
| Cenozoic Era | most recent era of earth's history; began about 66 mya when dinosaurs became extinct |
| continental drift | hypothesis that continents have moved around the globe to their present location |
| Pangaea | large landmass or supercontinent made up of all the present continents |
| subduction zone | area where denser ocean plate sinks under less dense continental plate |
| plate tectonics | theory that earth's crust and upper mantle are broken into sections that move around |
