| A | B |
|---|
| fossil | Any trace or remains of an organism that lived long ago |
| index fossil | distinct fossils used to determine the absolute age of rocks |
| Horizontality | Due to gravity, sediments are usually deposited in horizontal layers and eventually cement together to form sedimentary rock |
| Law of Superposition | States that in undisturbed sedimentary rock, older layers are on the bottom and younger layers are on top |
| Uniformitarianism | Geologic events that happen today happened the same way in the past |
| Petrification | A process in which an organism's tissues are completely replaced by minerals |
| relative dating | Comparing the age of raock layers without giving an actual age in numbers |
| fossil record | All of the fossils ever discovered on Earth |
| trace fossil | A fossilizied structure that was formed in sedimentary rock by animal acitivty |
| igneous intrusion | magma forced upward through layers of sedimentary rock that doesn't reach the Earth's surface |
| absolute dating | Using radiometric dating or index fossils to determine the actual age of a fossil or rock |
| radiometric dating | Method of comparing the ratio of parent isotope to daughter isotope in order to find the actual age of a rock or fossil |
| climate | weather conditions in an area over a long period of time |
| half-life | Time required for half of a sample of radioactive isotope to breakdown into a different isotope |
| Igneous extrusion | magma forced upward through layers of sedimentary rock that reaches the Earth's surface and makes a rock layer |
| Radioactive decay | The process in which a radioactive isotope tends to break down into a stable isotope of the same or of a different element |
| fault | A break in a rock due to an earthquake |
| strata | rock layer |
| isotope | an atom of an element that has a different number of neutrons |
| Geologic Column | A combination of rock layers from different locations that show the relative ages of layers that are not actually found together in nature |
