The author doesn’t issue any personal attacks against the scientists who came up with the sandstorm hypothesis. One can disagree with a hypothesis without suggesting anything about the wisdom of those who formed it. Since (A) doesn’t occur, it’s not the primary purpose.

This is the best answer. The author brings up the sandstorm hypothesis to contrast it with the sandslide hypothesis that’s discussed later. The central contrast is that the sandstorm hypothesis isn’t supported by evidence from sandstone, whereas the sandslide hypothesis is (see P2).

The author doesn’t mention the sandstorm hypothesis for the purpose of explaining the geological evidence for it. Rather, the author intends to show the sandstorm hypothesis isn’t supported by the evidence, whereas a different hypothesis is.

The author never suggests that previous support for the sandstorm hypothesis has impeded research. Since (D) doesn’t occur, it can’t be the primary purpose.

The author never suggests that people who formed the sandstorm hypothesis “ignored” evidence. It may be that there is evidence that shows the sandstorm hypothesis is wrong. But this doesn’t mean that the people who formed the hypothesis ignored it. Perhaps that evidence wasn’t around when the hypothesis was formed. In any case, even if people ignored evidence, the purpose of mentioning the hypothesis isn’t to show that people ignored evidence. It’s to setup discussion of the sandslide hypothesis later.