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Earth review 2

name: ______________________________
Across
Specific fossils used to identify geologic periods and match rock layers.
A quality of an element, where it suddenly changes into another element by giving off energy or small bits of matter.
A technique used to date materials, based on a knowledge of the decay rates of naturally occurring isotopes and the current amounts.
Down
The length of time that it takes for half the original number of radioactive atoms to change into some other kind of atom.
All of the fossils that have existed throughout life's history, whether they have been found or not.
The study of tree rings for growth and age information.
The study of rock layers