Question

nautilids are marine mollusks that begin growing their shells before emerging from their eggs and continue to add shell segments throughout their lifetimes. the walls between their shells chambers are called septa, and the concentration of the isotope oxygen - 18 they contain exactly reflects the isotopes concentration in the water at the depth at which the septa formed. paleontologist amane tajika and colleagues examined each of the septa in two nautilid shells; finding that sample f13 had a higher concentration of the isotope than sample m03 did, the researchers concluded that f13 must have formed at a significantly lower temperature than m03 did. which finding, if true, would most directly support the researchers conclusion? a) as the concentration of oxygen - 18 in water decreases, water temperature decreases and nautilid shell growth slows. b) as water depth increases, both the concentration of oxygen - 18 and the water temperature decrease. c) as water depth increases, the concentration of oxygen - 18 increases and water temperature decreases. d) as water temperature increases, decreases.

Explanation:

The researchers concluded that higher isotope concentration means lower temperature. We need to find a statement that supports this relationship between oxygen - 18 isotope concentration in nautilid shells, water temperature and depth. Option B shows that as water depth increases (which is related to temperature changes in the context), the concentration of oxygen - 18 decreases, aligning with the idea that lower oxygen - 18 concentration is associated with higher temperature (since the opposite of what the researchers found for lower temperature - higher oxygen - 18).

Answer:

B. As water depth increases, both the concentration of oxygen - 18 and the water temperature decrease.