| Term | Definition |
|---|
| Relative Dating | method for determining if an event or rock is younger or older than others. |
| Principle of Original Horizontality | layers of sediment that are generally deposited in a horizontal or nearly horizontal position |
| Law of Superposition | The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it. |
| Principle of Cross Cutting Relationships | Principle that a fault or intrusion is younger than the rock layers affected by it |
| Strata | Distinct layers of rock |
| Igneous Intrusion | always younger than the rock it has intruded, cross cuts |
| Unconformity | a place where an old, eroded rock surface is in contact with a newer rock layer |
| Unformitarianism | a principle that states that geologic process that occured in the past can be explained by current geological process |
| Correlation | establishing the equivalence of rocks of similar age in different areas |
| Fossil | the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil |
| Index Fossil | a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found |
| Absolute Age Dating | uses radioactive decay to determine an exact age |
| Half-Life | the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate) |
| Radiometric Dating | the procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes |
| Radiocarbon Dating | method measuring the decay rate of carbon isotopes in organic matter to provide dates for organic materials like wood or fiber |
| Isotope | one of two or more atoms with the same atomic number but with different numbers of neutrons |
| Parent Isotope | an unstable radioactive isotope |
| Daughter product | radioactive decay resulting from the parent isotope |
| Radioactivity | Spontaneous emission of radiation by some elements |
| Geologic Time Scale | the division of Earth history into blocks of time--eons, eras, periods, and epochs. The time scale was created using relative dating principles. |
| Principle of Inclusion | States that the pebbles cemented into a sediment matrix are older than the matrix itself |
| Faunal Succession | That certain fossils will never be found together. You can identify a strata of rock by its fossils |
| Shields | expansive, flat regions composed of deformed crystalline rock found within the stable interiors of continents, made by erosion of ancient mountain systems, ex: Canadian Shield in northeast North America |
| Stromatolites | fossilized bacteria grew like stacks of pancakes, estimated at 3 billion years old, one of the oldest living things found on Earth |
| Gondwana | late Paleozoic continent that formed the southern portion of Pangaea, consisting of all or parts of present-day South America, Africa, Australia, India, and Antarctica |
| Laurasia | Late Paleozoic, Northern Hemisphere continent composed of the present-day continents of North America, Greenland, Europe, and Asia |
| Dinosaur | any of numerous extinct terrestrial reptiles of the Mesozoic era |
| Gymnosperm | plant that produces seed that are not enclosed by a protective fruit |
| Mammal | a warm-blooded vertebrate with hair or fur and females produce milk to feed their young |
| Angiosperm | flowering plant; bears its seeds within a layer of tissue that protects the seed |
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