| A | B |
|---|
| rock cycle | a series of processes on and in Earth that change rocks from one kind to another |
| relative age | age of a rock compared to ages of other rocks |
| law of superposition | in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it |
| intrusion | always younger than the rock layers around and beneath it |
| index fossil | fossils of organisms that were widely distributed but only lived during a short period of time, used for relative dating |
| radioactive decay | when atoms of an unstable element break down to form atoms of another element, used by scientists to determine absolute age |
| half-life | the time it takes for half of a radioactive element to decay |
| igneous rocks | radioactive dating works best with this type of rock |
| Precambrian time | includes most of Earth's history, began with the formation of Earth, the first life appeared |
| theory of plate tectonics | pieces of Earth's outer layer are in constant slow motion |
| geologic time scale | a record of life forms and geologic events in Earth's history |
| ozone formed | 2.5 billion years ago when many organisms began using photosynthesis to make food, the amount of oxygen increased, forming this. |
| pangaea | Earth's continents moved together to form a supercontinent called |
| cambrian explosion | organisms that were invertebrates that lived in the sea evolved during this time of the Paleozoic era |
| amphibian | an animal that spends part of its life on land and part of its life in water |
| dinosaurs | an object from space that struck Earth caused the mass extinction of this group of organisms |
| uniformitarianism | the same geologic processes that operated in the past are still happening today |
| single-celled organisms | main type of living thing that existed during the Precambrain time |
| fault | a break in Earth's crust, always younger than a rock it cuts through |
| Earth and Moon | 4.6 billion years old |
| unconformity | a gap in the geologic record where some rock layers have been lost because of erosion |
| carbon-14 | radioactive element used to determine the age of organic remains |
| jawless fishes | first vertebrate |
| mesozoic era | known as age of the reptiles |
| periods | geologic time scale is divided into eras, which are further divided into _______ |
