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Chapter 6 Sections 1-3

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species
a group of organisms that are physically similar and can mate with each other and produce offspring that can also mate and reproduce
fossil
the preserved remains or traces of an organism that lived in the past
adaptation
a behavior or physical characteristic that allows an organism to survive or reproduce in its environment
evolution
the gradual change in a species over time
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
variation
any difference between individuals of the same species
homologous structures
body parts that are structurally similar in related species and that provide evidence for a common ancestor
branching tree
a diagram that shows how scientists think different groups of organisms are related
petrified fossil
a fossil formed when minerals replace all or part of an organism
mold
a type of fossil formed when a shell or other hard part of an organism dissolves, leaving an empty space in the shape of the part
cast
a type of fossil that forms when a mold becomes filled in with minerals that then harden
relative dating
a technique used to determine which of two fossils is older
radioactive dating
a technique used to determine the actual age of a fossil on the basis of the amount of a radioactive element it contains
half-life
the time it takes for half of the atoms in a radioactive element to decay
fossil record
the millions of fossils that scientists have collected
extinct
when no members of a species are alive
gradualism
the theory that evolution occurs slowly but steadily
punctuated equilibria
the theory that species evolve during short periods of rapid change
radioactive element
an unstable element that breaks down into a different element