Passage
For decades, climatologists have debated the primary driver of the mid-Holocene transition, a period marked by rapid aridification of the Green Sahara. Dr. Marcus Vance argues that a subtle shift in Earth's orbital parameters—specifically a decrease in summer solar radiation—triggered a sudden feedback loop in vegetation-atmosphere dynamics, leading to the collapse of the African monsoon. To support this orbital-collapse model, Vance cites oceanic sediment cores showing a sharp increase in dust deposition around years ago. However, Dr. Sylvia Moreno argues that this transition was far more gradual, pointing to fossilized pollen data from ancient lake beds that suggest a slow, localized decline in shrub cover spanning nearly two millennia. Moreno contends that oceanic dust records are a misleading proxy for regional precipitation because high-altitude winds can transport dust over thousands of miles from sources outside the Sahara, artificially compressing the apparent timeline of vegetation loss.
Which of the following discoveries, if true, would most directly undermine the credibility of Moreno's critique of Vance's evidence?
- Chemical analysis of the dust particles in the sediment cores matches the unique mineral signature of Saharan soil rather than soil from other global dust sources.Cevap
- BFossilized pollen from lake beds in nearby regions shows that vegetation loss occurred simultaneously across the entire African continent.
- CThe orbital shift cited by Vance occurred precisely at the start of the -year aridification period.
- DOceanic dust deposition rates are generally more variable than pollen deposition rates in lake beds.