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Radiometric dating

a method of determining the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.


unstable isotopes that break down and give off energy in the form of charged particles (radiation)


the time required for half of a sample of a radioactive substance to disintigrate by radioactive decay or by natural processes


Short chains of amino acids that gather into tiny droplets in water


the trace or remains of an organism that lived long ago, preserved in sedimentary rock


a bacterium that can carry out photosynthesis, such as a blue-green alga


a classification kingdom that contains all prokaryotes except archaebacteria


a classification kingdom made up of bacteria that live in extreme environments; differentiated from other prokaryotes by various important chemical differences


a mutually beneficial relationship in which one organism lives within another


an organism that belongs to the kingdom protista

extinction (extinct)

describes a species of organisms that has died out completely

mass extinction

an episode during which large numbers of species become extinct


a symbiotic associations between fungi and plant roots


a relationship between two species in which both species benefit


a member of the phylum Arthropoda, which includes invertebrate animals such as insects, crustaceans, and arachnids; characterized by having segmented bodies and paired appendages


an animal that has a backbone; includes mammals, birds, reptiles, amphibians, and fish

continental drift

the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations

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