PT117 · S4 · Q17 Climatologists believe they know why

This provides the classic form of When Cause is Absent, Effect is Absent strengthener (aka "no cause, no effect"). Since the ice ages started 800,000 years ago, if the author thinks that passing through cosmic dust is the cause, he must be thinking that the cosmic dust phenomenon started 800,000 years ago. By affirming this assumption, we're adding to the plausibility of the hypothesis.

This adds plausibility in the Suspect was at the Scene of the Crime style. In order for passing through clouds of dust to be the cause of ice ages that began 800,000 years ago, we need there to be clouds of dust existing 800,000 years ago. This is not only establishing that there are orbiting clouds of dense dust through which Earth might pass, but it also establishes that these clouds originated 800,000 years ago, at the same time that the ice age cycle started. So it also provides a When Cause Began, Effect Began type idea.

This adds some plausibility to the author's hypothesis by corroborating the Causal Mechanism the author is envisioning. She is saying that passing through clouds of cosmic dust leads to dust entering the atmosphere, which leads to the dust dimming the Sun. This answer presents a somewhat similar occurrence in which dense dust in the atmosphere leads to global cooling. It's not a powerful strengthener, but adds some credence to this storyline that "dust in the atmosphere leads to global cooling". Most people come down to (C) and (D) on this question, and notice (that on EXCEPT questions) the answer that did strengthen was designed to be unappealing or different in some way (volcanoes?!) Meanwhile, the correct answer, which was actually irrelevant, is designed to look appealing because it parrots keywords like "cosmic and dust".

This is strengthening by leaving Fingerprints. Weird and rare trace elements show up in sediment that was formed during ice ages. According to the author, during an ice age, the atmosphere was filled with cosmic dust from these clouds. The particulates in the atmosphere get trapped in sediment (that's how we later learn about different atmospheric composition of different time periods on Earth). The author's cosmic dust cloud hypothesis would not only explain ice ages but would also potentially explain a related curiosity: why do we find rare elements in the sediment that comes from ice ages? Where did those rare elements come from, and why is it during ice ages? The author could say, "Like I've been saying ... the Earth passes through these clouds of cosmic debris now and then, the dust from the debris leaks into the atmosphere and leads to an ice age; it would also mean that some of this cosmic dust is going to get trapped in layers of sediment.