| A | B |
|---|
| Paleontologists | scientists who study fossils |
| fossils | remains, imprints or traces of prehistoric organisms |
| permineralized remains | fossils in which paces inside are filled with minerals from groundwater |
| carbon film | results when a thin film of carbon residue forms a silhouette of the original organism |
| mold | a cavity in rock left when the hard parts of an orginism decay |
| cast | is formed when mineral rich water fills a mold left by organism |
| original remains | left when the organism has been trapped in amber, or frozen in ice |
| trace fossils | evidence of an organism's activities |
| index fossils | abudnant, geographically widespread organism that existed for relatively short periods of time |
| principle of superposition | process of reading undisturbed rock layers |
| oldest rock layers | found on the bottom of undisturbed rock layers |
| youngest rock layers | found on top of stacks of undisturbed rock layers |
| relative age | the age of something compared to something else |
| unconformities | any gap in rock layers |
| angular unconformity | rock layers are tilted, eroded then younger rocks form on top of eroded surface |
| disconformity | a layer of horizontal rock once exposed and eroded before younger rocks formed on top |
| nonconformity | sedimentary rock that forms over eroded metamorphic or igneous rock |
| absolute age | is age in years of a rock or other object, determined by properties of atoms |
| radioactive decay | unstable isotopes break down into other isotopes and particles |
| Beta decay | an isotope's neutron breaks down into a proton and an electron with the electron leaving the atom as a beta particle |
| alpha decay | as isotope gives off two protons and two neutrons as an alpha particle |
| half life | the time it takes for half the atoms in an isotope to decay |
| radiometric dating | calculating the absolute age of a rock using the ratio of parent isotope to daughter product and the half-life of the parent |
| potassium argon dating | is used to date ancient rock millions of years old |
| carbon 14 dating | is used to date bones, wood and charcoal up to 75,000 years old |
| Earth's age | is estimated to be 4.5 billion years old |
| oldest known rock | are estimated to be 3.96 billion years old |
| uniformitarianism | Earth processes occurring today are similar to those that occurred in the past |
| 5730 years | half life of carbon 14 |
| carbon | element found in tissues of most organisms |
| crinoid | state fossil of Missouri |
| under water | the area that is Missouri in ancient times |
| mountain building | forces whicy overturn layers of rocks |
