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radioactivity: The emission of energy due to changes in the nucleus of an atom. Such spontaneously released radiation is a characteristic of certain elements and at some levels can be harmful.
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radiometric dating: A dating technique that uses the decay rate of radioactive isotopes to estimate the age of an object.
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relative dating: The process of ordering fossils, rocks, and geologic events from oldest to youngest. Because of the way sedimentary rocks form, lower layers in most series are older than higher layers, making it possible to determine which fossils found in those layers are oldest and which are youngest. By itself, relative dating cannot assign any absolute age to rocks or fossils.
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RNA: Ribonucleic acid. Messenger RNA, ribosomal RNA, and transfer RNA are its three main forms. These act as the intermediaries by which the hereditary code of DNA is converted into proteins. In some viruses, RNA is itself the hereditary molecule.
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science: A way of knowing about the natural world based on observations and experiments that can be confirmed or disproved by other scientists using accepted scientific techniques.
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speciation: Changes in related organisms to the point where they are different enough to be considered separate species. This occurs when populations of one species are separated and adapt to their new environment or conditions (physiological, geographic, or behavioral).
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species: The biological species concept is the most widely accepted method for categorizing living species, especially for vertebrates. It defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define a biological species.
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supernatural: Relating to phenomena that cannot be described by natural laws, cannot be tested by scientific methodology, and are therefore outside the realm of science.
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taxonomy: The theory and practice of biological classification.
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theory: A well-substantiated explanation of some aspect of the natural world that typically incorporates many confirmed observations, laws, and successfully verified hypotheses.
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trait: A characteristic or condition.
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Young Earth Creationism (YEC): The belief that the Earth came into being only a few thousand years ago. Most young-Earth creationists base their belief on a literal interpretation of the Bible.
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