Question 120·Hard·Central Ideas and Details
The following excerpt is from an article by planetary scientist Dr. Leila Monroe discussing common misconceptions about Mars.
When popular media depict Mars as a barren red desert, they are only partially correct. The planet’s surface is indeed rich in iron oxide, giving it a rusty hue, but Mars’s palette is far more varied than casual observers imagine. Orbiters have photographed lavender dusk skies, pale blue sunrise tints, and streaks of seasonal carbon dioxide frost that gleam white against charcoal-toned dunes. Even the “red” soil is not uniformly colored; wind scours some slopes to reveal chocolate-brown basalt while exposing patches of yellowish sulfur compounds elsewhere. By compressing these complexities into a single color, we flatten the planet’s dynamic geologic story and, more importantly, risk missing chemical clues that could hint at past habitability. Mars is not just red; it is a mosaic whose subtle shades record billions of years of environmental change.
Which choice best states the central idea of the text?
For central idea questions, start by reading the whole passage, then focus on the first and last sentences to see how the author frames and concludes their main point. Ask yourself, “What is the author arguing overall, beyond the specific examples?” Then eliminate choices that (1) focus on a small detail, (2) introduce ideas or extremes not stated in the passage, or (3) contradict parts of the text. The correct answer should capture the broad message that all the details are supporting.
Hints
Use the beginning and end of the passage
Reread the first and last sentences. What problem with media depictions does the author point out at the beginning, and how is that idea completed or clarified in the final sentence?
Focus on the author’s main claim, not the examples
The colors and features listed (lavender skies, white frost, brown basalt, etc.) are there to support something. Ask yourself: What bigger point are these examples proving?
Eliminate choices that are too narrow or add new ideas
Look for answer choices that only mention one detail (like iron oxide) or introduce ideas the passage doesn’t state (such as strong limits on what scientists can do). The central idea should cover the whole paragraph.
Step-by-step Explanation
Identify what the question is asking
The question asks for the central idea of the text. That means you need the main point or overall message of the whole passage, not a small detail or side note.
Use the first and last sentences to frame the main point
Look at the first sentence: it says media depictions of Mars as a barren red desert are “only partially correct.” That suggests the author thinks this common picture is incomplete.
Now look at the last sentence: “Mars is not just red; it is a mosaic whose subtle shades record billions of years of environmental change.” This tells you the main idea: Mars is more than just red, and its many colors tell a long, important geological story.
Check how the middle of the passage supports that idea
The middle of the passage gives many examples of different colors on Mars: lavender skies, pale blue tints, white frost, charcoal dunes, chocolate-brown basalt, yellowish sulfur compounds. Then the author says that by compressing all this into a single color, “we flatten the planet’s dynamic geologic story” and “risk missing chemical clues” about habitability.
So the details show two key things:
- Mars has a diverse range of colors.
- Those colors are scientifically important, telling us about geology and possible past habitability.
Match the overall message to the best answer choice
Now compare each option to that overall message:
- A focuses on iron oxide making Mars look redder from orbit, which is just one detail and not the main point.
- B says media are wrong because Mars is mainly brown and yellow, but the passage says Mars has many colors (including red), not that it is mostly brown and yellow.
- C claims scientists are unable to study Mars’s colors accurately, which the passage never says.
- D says that Mars’s perceived redness oversimplifies its diverse and informative colors, which fits the author’s claim that “Mars is not just red” and that its subtle shades record billions of years of environmental change.
Therefore, the best answer is D) Mars’s perceived redness oversimplifies the planet’s diverse and informative range of surface colors.