Here is my ananlysis of the argument:
Conclusion : "The scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae such as diatoms."
THe author mentions that the increase in the amount of ferrous material in the atmosphere has increased the population of the algae in antartica. The only way to weaken this argument would be to show the decreament in the amount of algae in any way or to show that the decreament in the amount of algae is actually because of some other reason.
The reason why the author mentions the increase in the increase in the amount of algae is because of the decreament in the amount of CO2 in the atmosphere. So, the unhidden premise is that the number of algae during the last ice age is that
1.
The decreament in the amount of CO2 cannot be done by the existing number of algae before or during the ice age, it had to increase and as mentioned in the argument due to the increase in population of algae the amount of CO2 decreased.
2. There is no other reason for the decreament of CO2 in the atmosphere of the antartic in the last ice age.
The only way to weaken the argument would be to attack the above 2 assumptions or something on the line of that.
Option (D) says that "Sediment from the ocean floor near Antarctica reflects no increase, during the last ice age, in the rate at which the shells that diatoms leave when they die accumulated.", which esssentially means that the death rate of the algae practically remained the same and did not change throughtout the given period of time.
My question : IF my above explaination is correct, then on what basis are we claiming option (D) to be a weakener.
Kindly please help me clarify my understanding.
Sajjad1994 @KarsihmaB
GMATNinja nightblade354