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Earth History Crossword Puzzle

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Earth History

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                  15     16                   17              
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6 Method useed to determine the absolute age of a rock by measuring the amounts of parent and daughter materials in a rock
7 A type of rock that has been profoundly changed by heat and/or pressure into another kind of rock
8 An organism with a 3-lobed exoskeleton; considered an index fossil
9 The principle that Earth processes today are similar to those that ccurred in the past
10 The divisions of earth's geologic time based on the life forms that lived only during certain periods
11 To determine the age, in years, of rocks by studying the properties of atoms in rocks
12 Breaking down of isotopes
13 Type of rock formed when layers of sediment are pressed and cemented together
15 A process by which organisms with characteristics better suited to a certain enviornment have a better chance of surviving and reproducing than organisms that do have these characteristics
18 Fractures in contunity of a rock formation
19 Remains, imprints, or traces of prehistoric organisms
20 Samples of ice taken from glaciers that provide evidence of past atmospheric condtions
1 To determine the approximate age of a rock or other object in comparison to something else
2 A method of dating bones
3 The time it takes for half of the atoms that are isotopes to decay
4 A silvery-white metallic chemical element in the actinide series of the periodic table; weakly radioactice because its isotopes are unstable
5 If rocks are undisturbed, the older layers of rock are under the younger layers of rock
14 Remains of species that existed on earth for a relatively short period of time; can be used by geologist to assign the ages of rock layers
16 Any gap in a rock record, or incomplete rock layer
17 Rock formed through the cooling and solidification of magma or lava
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