| A | B |
|---|
| paleontologist | scientists which look for clues to help them reconstruct the past |
| relative dating | ordering fossils to determine their ages |
| half-life | the time it takes for half of the unstable atoms in a sample to decay |
| absolute dating | estimation of the age of a rock sample and the fossil it contains |
| fossils | traces of living things preserved in rock |
| rock cycle | process by which one rock changes into another |
| geologic time scale | calendar scientists use to outline the history of life on earth |
| mass extinctions | periods of large-scale extinctions |
| extinct | description of a species which dies out completely |
| plate tectonics | movement of the earth's crust |
| Pangaea | single landmass on Earth long ago |
| Precambrian time | a time before 540 mya when only very primitive organisms lived |
| prokaryote | a cell without a nucleus |
| anaerobic | cells which do not need oxygen |
| ozone | gas which absorbs UV light from the sun |
| eukaryotes | complex life-forms having cells with nuclei |
| Paleozoic era | 540 mya - 248 mya, "ancient life", or the Age of Fishes |
| Mesozoic era | 248 mya - 183 mya, "middle life", or the Age of Reptiles |
| Cenozoic era | 65 mya - today, "recent life", or the Age of Mammals |
| hominids | humans and their ancestors |
| prosimians | first primates, like lemurs |
| australopithecines | "southern man ape", among the oldest hominids |
| Neanderthals | hominids which lived 230,000-30,000 years ago |
| Cro-Magnons | hominids with modern features, existed 100,000 - 35,000 years ago, the first modern humans |
