Fossils May Be

Absolute dating uses ________ to estimate how old a fossil is. A) depth within rock layers B) radioactive isotopes C) a molecular clock D) structural features E) embryonic structures

If an isotope's half-life is 100 years,then A) that isotope will no longer exist in 50 years. B) that isotope will no longer exist in 200 years. C) in 50 years only half of the atoms in a sample of that isotope will remain. D) in 100 years only half of the atoms in a sample of that isotope will remain. E) in 200 years only half of the atoms in a sample of that isotope will remain