Asia’s Gobi Desert and California’s Central Valley are the main sources of dust in western North America’s Sierra Nevada mountains. To investigate their relative contributions, Elena Navarro et al. recorded the isotopic signatures of dust collected at a low elevation site (the Pine Creek Experimental Range) and two higher elevation sites (Bear Meadow and Alder Ridge) in the Sierra Nevada, as well as the isotopic signatures of Gobi and Central Valley dust. Navarro et al. concluded that while the contribution of Central Valley dust, which has a lower ratio of strontium-87 to strontium-86 (87Sr/86Sr) than Asian dust does, remained mostly unchanged at the lowest elevation site for the duration of the study, the contribution of Central Valley dust increased at higher elevations.
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Verbal·Information and Ideas·Command of Evidence
hardWhich finding, if true, would most strongly support the researchers’ conclusion?
A
By the end of the study, the 87Sr/86Sr ratios of dust collected at Bear Meadow and the Pine Creek Experimental Range had become very similar, whereas the 87Sr/86Sr ratio of dust collected at Alder Ridge showed no significant change.
B
Over the course of the study, the 87Sr/86Sr ratio of dust collected at the Pine Creek Experimental Range was relatively constant, whereas the 87Sr/86Sr ratios of dust collected at Bear Meadow and Alder Ridge decreased.
C
Throughout the study, the 87Sr/86Sr ratio of dust collected at the Pine Creek Experimental Range was consistently higher than the 87Sr/86Sr ratios of dust collected at Bear Meadow and Alder Ridge.
D
As the study went on, the 87Sr/86Sr ratios of dust collected at Bear Meadow and Alder Ridge grew closer to the 87Sr/86Sr ratio of dust from Asia, whereas the 87Sr/86Sr ratio of dust collected at the Pine Creek Experimental Range grew closer to the 87Sr/86Sr ratio of dust from the Central Valley.