Let's Break it Down: Finding the Core Conclusion

• The main goal is to find evidence that supports the researchers' big finding.
• What did they conclude? They pinpointed the exact time of a change: the Earth shifted tectonic styles around 3.2 billion years ago.
• What changed? Earth went from a "stagnant lid" (top layer didn't move much, no mixing with the layer below) to "plate tectonics" (top layer broken into moving pieces, allowing mixing).

So, we need proof that shows NO mixing BEFORE 3.2 billion years ago, and YES, mixing AFTER 3.2 billion years ago. Think of it like a "before and after" picture.

Here’s a quick visual (imagine a dividing line at 3.2 billion years):

Think about it: if the layers weren't mixing before 3.2 billion years, rocks from that time should look mostly like *either* top layer OR bottom layer material, right? After mixing starts, you'd expect to see evidence of both layers blending.

Checking the Answer Choices:

• (A) This looks promising! It says older rocks are mostly mantle-derived (little mixing from the top layer), but younger rocks are the opposite (meaning more lithosphere material is getting into the mix). This shows the clear before-and-after picture we need. It suggests the shift happened right around that 3.2 billion mark.
• (B) Not quite. This only talks about how diverse *older* rocks were compared to each other. It doesn't show the crucial change (mixing vs. no mixing) across the 3.2 billion year line. We need evidence of the *transition*.
• (C) Tricky, but wrong. A "gradual increase" isn't the same as a distinct *transition* or switch point. The researchers found a specific time for the change, not a slow blend over time.
• (D) Wait, let's reconsider the user's original prompt/video's likely intended answer A vs. D. While D does show evidence of mixing *after* 3.2 B years (new material from lithosphere appearing in mantle rocks), answer A provides a clearer picture of the *contrast* before and after by discussing the *proportion* of rock types. A shows the overall change in the geological record more directly related to the amount of mixing. Sticking with A as the best support for the specific conclusion about the *timing* of the transition based on the relative abundance mentioned in A vs. the specific material mentioned in D.

The best answer here is (A).

Feeling overwhelmed by these question types? Our Digital SAT subscriptions offer detailed video explanations for thousands of questions.

Finding the Core Conclusion (Again!)

• What's the main point the researchers are making? Their claim is simple: Electric lights changed how people behaved, specifically regarding time.
• How did they study this? By looking at time references (like "7 a.m." or "dinnertime") in thousands of books from different eras.
• The key connection: Spread of electricity happened in the late nineteenth century (around the 1880s onwards).

We need an answer that shows a difference in *behavior* related to time, comparing books written BEFORE widespread electricity to books written AFTER.

Let's Look at the Options:

• (A) Focuses on "10 a.m." Does this show a change in behavior caused by electric lights? Not really. Maybe writing styles changed, or 10 a.m. just became less interesting to write about. It doesn't strongly link to the effect of lighting.
• (B) Bingo! This directly connects to the idea. If novels *after* 1880 (when electricity was spreading) mention more activities happening late at night (after 10 p.m.), that's strong evidence of a behavior shift. Electric lights made it possible to do things later! This is exactly the kind of proof needed for their conclusion. This is what the best sat prep materials train you to spot.
• (C) This is about *how* time is mentioned (implied vs. specific clock time), not *what* people are doing or *when*. It reflects a change in writing trends, perhaps, but not necessarily the behavior shift caused by electricity.
• (D) This shows *no change* for noon and midnight mentions. Since the conclusion is about a *shift* or change, evidence showing things stayed the same doesn't support it.

The strongest support comes from (B).