What makes life on the Earth possible?

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Explanation:

Earth's amazing gaseous atmosphere is responsible for making life possible on this, the third planet from the Sun. Our atmosphere contains water vapor which helps to moderate our daily temperatures. Our atmosphere contains 21% oxygen, which is necessary for us to breathe, 78% nitrogen,

Option B, This situation represents isolation by vicariance.

Explanation:

Isolation by variance occurs when geographical barriers occur in a habitat that lead to unevenly distribution of population.  

Here in this case the dam on the river is a barrier to the stability of habitat (island) of ants

“Isolation by variance” differs from “isolation by dispersal” as in “isolation by dispersal”, the population of a given species crosses a barrier that already exists.

Hence, the correct answer is option B