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, Sarah Aciego et al. recorded the isotopic signatures of dust collected at a low elevation site (the San Joaquin Experimental Range) and two higher elevation sites (Providence and Soaproot) in the Sierra Nevada, as well as the isotopic signatures of Gobi and Central Valley dust. Aciego 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
mediumWhich finding, if true, would most strongly support the researchers’ conclusion?
A
Over the course of the study, the ⁸⁷Sr/⁸⁶Sr ratio of dust collected at the San Joaquin Experimental Range was relatively constant, whereas the ⁸⁷Sr/⁸⁶Sr ratios of dust collected at Providence and Soaproot decreased.
B
As the study went on, the ⁸⁷Sr/⁸⁶Sr ratios of dust collected at Providence and Soaproot grew closer to the ⁸⁷Sr/⁸⁶Sr ratio of dust from Asia, whereas the ⁸⁷Sr/⁸⁶Sr ratio of dust collected at the San Joaquin Experimental Range grew closer to the ⁸⁷Sr/⁸⁶Sr ratio of dust from the Central Valley.
C
Throughout the study, the ⁸⁷Sr/⁸⁶Sr ratio of dust collected at the San Joaquin Experimental Range was consistently higher than the ⁸⁷Sr/⁸⁶Sr ratios of dust collected at Providence and Soaproot.
D
By the end of the study, the ⁸⁷Sr/⁸⁶Sr ratios of dust collected at Providence and the San Joaquin Experimental Range had become very similar, whereas the ⁸⁷Sr/⁸⁶Sr ratio of dust collected at Soaproot showed no significant change.