The time it takes for half of a radioisotope's atoms to decay ____
a. cannot be calculated
b. is used to construct the geologic time scale
c. is its half-life
d. is the same for uranium 238 and carbon 14
e. is highly variable
ANSWER: c
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A) chlorophyll a B) chlorophyll c C) lutein D) phycoerythrin E) ?-carotene
The protoplanet nebula model states that the simplest and most abundant gases would have been
A. hydrogen and helium. B. oxygen and carbon dioxide. C. nitrogen and hydrogen. D. hydrogen and oxygen.
A woman is considered to have reached menopause when ____.
A. her menstrual cycles have diminished B. her follicles are depleted C. her follicles have regenerated D. her eggs are mature E. her eggs dissolve