|Question 11Verbal

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The late Hemphillian (Hh) North American Land Mammal Age includes the subdivisions Hh3, 6.8 million years ago (Ma) to 6 Ma, and Hh4, 6 Ma to 4.75 Ma. While mammalian fossils have indicated that Florida's Montbrook Fossil Site (MFS) and Palmetto Fauna of the Bone Valley Region (PFBV) date to Hh4, a more precise determination of the sites' ages has proved challenging. Stephanie R. Killingsworth et al. compared average ratios of strontium-87 to strontium-86 (87Sr/86Sr) in fossil shark teeth from MFS and PFBV --- 0.709000 and 0.709028, respectively --- to 87Sr/86Sr ratios in the global strontium seawater curve, a record that shows how 87Sr/86Sr ratios in seawater correspond to numerical ages and that is used to date fossils and, by extension, fossil sites. The researchers concluded that ______
Which choice most effectively uses data from the graph to complete the assertion?
mammalian fossil evidence offers less dating precision than do 87Sr/86Sr ratios in fossil shark teeth and that PFBV likely was deposited closer to the Hh3-Hh4 boundary than was MFS.
A
the average 87Sr/86Sr ratios in the fossil shark teeth from MFS and PFBV resolve previous uncertainty about the sites' relative ages by indicating that both sites were deposited contemporaneously during the late Hh.
B
the average 87Sr/86Sr ratios in the fossil shark teeth from MFS and PFBV only partially support the site age estimates previously established through mammalian fossil evidence.
C
the average 87Sr/86Sr ratios in the fossil shark teeth from MFS and PFBV corroborate that both MFS and PFBV fall within Hh4 but suggest that PFBV was likely deposited more recently than MFS
D