How can the ratios of oxygen isotopes be used to indicate past climate change? What marine substance can be tested for its oxygen ratios?
What will be an ideal response?
Answer: 16O and 18O both exist in seawater. Because 16O is lighter in weight, it will evaporate more readily from oceans. During glaciations, large volumes of water are evaporated from the oceans (and by extension, large quantities of 16O) and precipitated on land in the form of ice and snow, which creates glaciers. Therefore, the seawater becomes preferentially enriched in 18O, which is taken up by marine microorganisms when they create their shells. The higher the 18O content, the colder the climate.
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What will be an ideal response?
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