Why did shubin and daeschler search in the canadian arctic for fossil evidence of the transition from fish to tetrapods?

The correct answer is this one: "2)They hypothesized that the transitional fossils were in volcanic rocks older than 365 million years ago, when the first tetrapods appear in the fossil record."

There exists the same question with the following choices:
 1)They hypothesized that the transitional fossils were in sedimentary rocks older than 365 million years ago, when the first tetrapods appear in the fossil record.
2)They hypothesized that the transitional fossils were in volcanic rocks older than 365 million years ago, when the first tetrapods appear in the fossil record.
3)They hypothesized that the transitional fossils were in sedimentary rocks older than 530 million years ago, when the first fish appear in the fossil record.
4)They hypothesized that the transitional fossils were in volcanic rocks older than 530 million years ago, when the first fish appear in the fossil record.