Question

text 1
chemically analyzing bulk rock - core samples from australias mount
mcrae shale, ariel anbar et al. found a transient but significant
increase in molybdenum (mo) at a point corresponding to roughly 2.5
billion years ago (ga). on earth, mo is released mainly through
oxidative weathering of minerals; anbar et al. therefore concluded that
atmospheric oxygen briefly increased 2.5 ga, then returned to its
earlier negligible level.
text 2
sarah stotznicki et al. reexamined the mount mcrae shale core.
since chemically analyzing bulk samples can exclude contextual
details, stotznicki et al. also employed high - resolution microscopy,
which revealed volcanic debris—known mo—lost around 2.5 ga and
microfractures in the surrounding matrix. the researchers assert that
fluid could have reached the debris through the microfractures and
initiated oxidative weathering long after debris deposition.
based on the texts, anbar et al. (text 1) and stotznicki et al. (text 2)
would most likely disagree about the answer to which question about
the portion of the mount mcrae shale rock - core corresponding to 2.5
ga?
a) is the increase in mo in that portion attributable to oxidative
weathering of the material found in that portion?
b) is the increase in mo in that portion indicative of an increase in
atmospheric oxygen dating to the same time?
c) did chemically analyzing bulk samples lead to a false
impression that there is an increase in mo in that portion?
d) does the increase in mo in that portion suggest that atmospheric
oxygen levels were not negligible before 2.5 ga?

Explanation:

• Text 1: Ariel Anbar et al. found an increase in molybdenum (Mo) at 2.5 Ga. Since Mo is released mainly through oxidative weathering of minerals, they concluded that atmospheric oxygen briefly increased at 2.5 Ga.
• Text 2: Sarah Stotznicki et al. used high - resolution microscopy and found volcanic debris (known Mo - lost around 2.5 Ga) and microfractures. They assert that fluid could have reached the debris through microfractures and initiated oxidative weathering long after debris deposition. So, the increase in Mo may not be due to the atmospheric oxygen at 2.5 Ga.

Answer:

B. Is the increase in Mo in that portion indicative of an increase in atmospheric oxygen dating to the same time?