| A | B |
|---|
| relative dating | determining whether an object or event is older or younger than other objects or events |
| superposition | a principle that states that younger rocks lie above older rocks in undisturbed sequences |
| geologic column | an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest |
| unconformity | a surface that represents a missing part of the geologic column |
| absolute dating | the process of establishing the age of an object, such as a fossil or rock layer, by determining the number of years it has existed |
| isotopes | atoms of the same element that have the same number of protons but have a different numbers of neutrons |
| radioactive decay | a process in which radioactive isotopes tend to break down into stable isotopes of other elements |
| radiometric dating | determining the absolute age of a sample based on the ratio of parent material to daughter material |
| half-life | for a particular radioactive sample, the time it takes for one-half of the sample to decay |
| geologic time scale | a scale that divides Earth's 4.6-billion-year history into distinct intervals of time |
| disturbing forces | forces from within the Earth that push, fold, tilt, break the layers |
| How do geologists use the geologic column | they compare their samples to it to figure out how old their samples are or if any events happened that disturbed their sample |
| feature | a change to the normal layers of rock. They are always younger than the rock layers they affect, because the layers had to be there first to have something happen to them. |
| faults | a feature that occurs when there is a break in the earth's crust where blocks of layers slide apart |
| intrusions | a feature that occurs when molten rock from deep inside the Earth that squeezes upwards and cools, disturbing the layers |
| folding | a feature that occurs when rock layers bend and buckle from the Earth's internal forces |
| tilting | a feature that occurs when the earth's internal forces slant the rock layers without folding them. |
| unconformities | when layers of rock are missing and there is a gap in the geological record. The gaps represent missing time. |
| nondeposition | when the sediment supply gets cut off and sediment stops being deposited - the missing sediment is a gap |
| erosion | when water, wind or other elements wear a layer away - the missing layer is a gap |
| disconformities | a type of unconformity where part of a sequence of parallel rock layers is missing. It is hard to see. |
| nonconformity | sedimentary rock layers lie on top of an eroded surface |
| angular unconformities | a gap between horizontal rock layers and rock layers that are tilted or folded. The parallel layers formed on top of the tilted layers. |
| Rock layer puzzles | rock layers that were affected by many unconformities. Scientists have to compare it to a geologic column to figure out what happened. |
| parent material | the atoms that are still unstable isotopes in a rock |
| daughter material | the atoms that have converted into stable isotopes by radioactive decay |
| ratio of parent to daughter isotopes | what scientists use to figure out the age of a volcanic |
| uranium-lead method | a type of radiometric dating that measures the ratio of uranium-238 (parent) to lead-206 (daughter. Can be used for rocks more than 10 million years old. Younger rocks don't have enough daughter material to be measured for these isotopes |
| potassium-argon method | a form of radiometric dating that measures the ratio of potassium (parent) to argon. This method is used for rocks older than 100,000 years. |
| Carbon-14 method | A type of radiometric dating that can be used on things that were alive. It measures the ratio of carbon 14 (parent) to carbon 12 (daughter) |
