| Term | Definition |
|---|
| species | a group of organisms that are physically and genetically similar and can mate with each other and produce offspring that can also mate and reproduce |
| adaptation | a behavior or physical characteristic that allows an organism to survive or reproduce in its environment |
| scientific theory | a well-tested concept that explains a wide range of observations |
| natural selection | a process by which individuals that are better adapted to their environment are more likely to survive and reproduce than others of the same species |
| competition | when two species vie with each other for the same resource |
| variation | differences between individuals within a population or among populations |
| fossil | the preserved remains or traces of an organism that lived in the past |
| petrified fossil | a fossil in which minerals replace all or part of an organism |
| trace fossil | a type of fossil in which the shape of the organism is preserved (example footprints) |
| cast fossil | a solid copy of the shape of the organism |
| mold fossil | a hollow area in sediment in the shape of an organism or part of an organism |
| preserved remains | part of the extinct organism is preserved with little or no change (decay hasn't fully happened) |
| extinction | the disappearance of all members of a species from Eearth |
| gradualism | the theory that evolution occurs slowly but steadily |
| punctuated equilibria | the theory that species evolve during short periods of rapid change |
| homologous structures | body parts that are structurally similar in related species |
| cladogram | a branching diagram showing the evolutionary relationships among a group of organisms |
| igneous rock | a type of rock that forms from the cooling of molten rock at or below the surface |
| absolute age | the age of a rock given as the number of years since the rock formed |
| relative age | the age of a rock compared to the ages of rock layers |
| radioactive dating | method used to determine the absolute age of rocks based on the time it takes a radioactive element to decay |
| 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 |
| extrusion | an igneous rock layer formed when lava flows onto Earth's surface and hardens |
| intrusion | an igneous rock layer formed when magma hardens beneath Earth's surface |
| fault | a break or crack in Earth's crust along which the rocks move |
| unconformity | a place where an old, eroded rock surface is in contact with a newer rock layer |
| index fossil | fossils of making an inference, an interpretation based on observations and prior knowledge |
| half-life | the time it takes for half of the atoms in a radioactive element to decay |
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