| A | B |
|---|
| geologic time scale | record of the geologic events & life forms in Earth's history |
| era | one of the three longest units of geologic time |
| period | the units of geologic time into which eras are divided |
| comet | ball of ice and dust that orbits the sun |
| continental drift | movement of continents slowly over Earth's surface due to forces inside Earth |
| invertebrate | animal without a backbone |
| vertebrate | animal with a backbone |
| amphibian | animal that lives on land and in the water |
| reptiles | animals with scaly skin that lay eggs with a leathery shells |
| mass extinction | many living things become extinct at the same time |
| Pangaea | supercontinent |
| mammal | warm-blooded vertebrate that feeds its young milk |
| Mesozoic Era | Age of Reptiles |
| Paleozoic Era | era before Mesozoic |
| Cenozoic Era | Age of Mammals |
| Precambrian Time | longest period in geologic time; first life appears on Earth |
