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Chapter 12 Terms
| Question | Answer |
|---|---|
| relative dating | a method of determining whether an event or object, such as a fossil, is older or younger than other events or objects without referring to the object's age in years |
| radiometric dating | a method of determining the absolute age of an object, often by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope |
| isotope | an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and a different atomic mass) |
| half-life | the time required for half a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope |
| index fossil | a fossil that is used to establish the age of a rock later because the fossil is distinct, abundant, and widespread and the species that formed that fossil existed for only a short span of geologic time |
| geological time scale | the standard method used to divide Earth's long natural history into manageable parts |
| era | a unit of geologic time that includes two or more periods |
| period | unit of geologic time that lasts tens of millions of years and is associated with a particular type of rock system |
| epoch | smallest unit of geologic time, lasting several million years |
| nebula | a large cloud of gas and dust in interstellar space, a region in space where stars are born |
| ribozyme | a type of RNA that can act as an enzyme |
| cyanobacteria | bacteria that carry out photosynthesis |
| endosymbiosis | a mutually beneficial relationship in which one organism lives within another |
| Paleozoic | era of geologic time (from 544 to 248 million years ago) during which members of every major animal group today evolved |
| Cambrian explosion | earliest part of the Paleozoic era, when a huge diversity of animal species evolved |
| Mesozoic | era during which dinosaurs roamed Earth (from 248 million years ago to 65 million years ago) |
| Cenozoic | geologic time period that began 65 million years ago and continues today |
| primate | the group of mammals that includes humans, apes, monkeys, and prosimians; typically distinguished by a highly developed brain, flexible hands and feet, forward-looking eyes, and enlarged brains relative to body size |
| prosimian | oldest primate group that includes mostly small, nocturnal primates such as lemurs |
| anthropoid | humanlike primate |
| hominid | a primate characterized by bipedalism, relatively long lower limbs, and lack of a tail; examples include humans and their ancestors |
| bipedal | animal that walks on two legs |
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