| A | B |
|---|
| uniformitarianism | current geologic processes are the same as those from the past |
| strata | rock layers |
| relative age | age of an object compared to another |
| bedding plane | boundary between 2 rock layers |
| law of superposition | older layers are below younger layers |
| unconformity | break in geologic record |
| principle of original horizontality | if undisturbed, sedimentary rock form horizontal layers |
| graded bedding | coarse or heavy particles are in the lowest layers |
| ripple marks | small waves on surface of sand caused by water or wind |
| law of crosscutting relationships | a fault or intrusion is younger than a rock layer it cuts across |
| absolute age | numeric age |
| varve | band of sand deposited each year |
| radiometric dating | using radioactive decay to determine absolute age |
| radioactive isotope | nuclei that emit particles at constant rate |
| parent isotope | original radioactive isotope |
| daughter isotope | newly formed isotope |
| half-life | time it takes for 1/2 the mass of parent isotope to decay into daughter isotope |
| carbon-14 dating | use carbon-14 to tell absolute age of dead organism |
| fossil | remains of once living organism |
| paleotology | study of fossils |
| trace fossils | fossilized marks left by once living organism |
| index fossil | fossil used to determine absolute age |
