The permian-triassic extinction 250 million years ago wiped out about ninety percent of earth's animal species. some scientists are predicting a sixth mass extinction in the future, due to a) acid rain. b) air pollution. c) global warming. d) earthquake activity.

Which two criteria must be met before scientist can use radiocarbon dating? explain your answer

Crinoids, also known as sea lilies, appear to be sea plants but are not plants at all. crinoids are an echinoderm species which uses anchoring structures called holdfasts to attach themselves to the sea floor. crinoids were most abundant in pennsylvania during the mississippian period, which ranged from 375 to 320 million years ago. fossils of the crinoids shows that during most of this time pennsylvania was that provided favorable conditions for crinoid growth. a) glacial terrain b) a dry and sandy plain c) mostly mountain ranges d) covered by warm, shallow seas

For each of the formulas, classify the formula as either an empirical formula, a molecular formula, or both. nahco3 empirical molecular both