Some atoms, such as carbon-14, whose nuclei are not stable, loose parts of their nucleus through decay. In the process they become another element. Atoms such as this are said to be ____.
half - atoms
radicals
isotonic
radioactive
Certain groups of fossils, which are commonly found in sedimentary rock, have been radiometrically dated and have been found to be a certain range of ages old regardless of where on earth they are found. Geologists have come to use these fossils as a marker for the relative age of the layer the fossils are found in. These types of fossils are called
trace fossils
marker fossils
index fossils
faunal fossils
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