Narrator: Listen to part of a lecture in an astronomy class.
Professor: This semester, we’ve been talking about the pros and cons of exploring Mars. We already know that it would be expensive, the practical benefits are uncertain, and it could be very dangerous. But, um… there are a lot of reasons to explore Mars. Let’s start with the Gale Crater. The Gale Crater is a massive crater on the surface of Mars. It’s somewhere between 3.5 and 3.8 billion years old. And right in the center of the Gale Crater is a huge mountain. Here’s an image of both the mountain and the crater.
This image is an elevation map of the Gale Crater. The Mars rover Curiosity first landed on Mars in the Gale Crater, specifically in the oval you see there, and it has been maneuvering around it, taking samples and pictures. The picture you see has been, ah… color-coded to show the different elevations. Obviously, the crater isn’t actually these colors, um, but it is easier to see the different elevations using this color-coded map. The deep blue shows the bottom of the crater… very low elevations. The orange-red in the center is the peak of the mountain, often referred to as Mount Sharp. Mount Sharp is approximately 5 kilometers high. This height is comparable to some of the Earth’s taller mountains. The Gale Crater has a diameter of about 150 kilometers… it’s a little bigger than Rhode Island and Connecticut combined.
Because both the crater and the mountain are so large and so old, they offer a huge amount of information to scientists. The mountain itself is made up of two different kinds of sediment. The base is mostly clay. Why? Well, the crater was originally made by a meteor hitting the surface of Mars. Some scientists theorize that the resulting crater filled with water, making it a giant lake, and this clay sediment comes from the lake bed. Above the clay, the sediment is composed of oxygen and sulfur-containing minerals. These are likely dirt and rocks that were blown into the crater by the wind after the lake dried up. Um, Lisa?
Female Student: How do they know that part came from the lake bed and part was just blown in?
Professor: Um, well, the form and composition of each rock depends on its environment. Y’know, there are some types of rocks that can only be formed in water, and some that can only be formed in the atmosphere. After analyzing the rock samples, um, much of the minerals in the higher portion of Mount Sharp can really only be formed by running water. Several areas on Mount Sharp look like ancient river and stream beds, which, um… would explain the origin of the oxygen and sulfur minerals.
Male Student: But if Mars had water, where is it now?
Professor: Most scientists theorize that the water evaporated into space. There is a study underway that would measure the elements in the atmosphere and compare them with the minerals on the ground. Scientists will be able to predict not only how much water was on the ground, but also when and how quickly it left the surface of the planet.
Female Student: But… I thought Mars didn’t have an atmosphere?
Professor: It doesn’t have much of one, that’s true. The atmosphere on Mars has about 1 percent of the atmospheric pressure on Earth. But there’s enough of it left that we can take measurements of the elements there.
Male Student: Why does all this ancient history matter? I mean, shouldn’t we be studying the Earth and not some distant planet?
Professor: Oh, there’s lots we can learn from this. For instance, if Mars did have water, it likely had it before Earth did. And that water might have supported life. Now, if it did, that means one of two things is true. Maybe the life that formed on Mars was the same as the life that formed on Earth, which means our ancestors—our bacterial ancestors—originally came from Mars, and arrived on Earth by meteors… so in a way, then we’d all be Martians. Or, maybe the life on Mars was different from ours. That would be definitive proof that we were not alone in the universe.
|
What is the main purpose of the lecture? |
Gist-purpose. The professor discusses the Gale Crater, a feature of Mars that he believes is particularly interesting. He uses it as an example of why exploring Mars is worthwhile. |
|
| ✗ | A To explain why scientists disagree about the formation of Mount Sharp |
Mount Sharp is discussed, but there is no disagreement mentioned about how it was formed. |
| ✓ | B To present a feature of Mars that should continue to be studied |
Correct. The professor primarily focuses on discussing the Gale Crater, and Mount Sharp at the center of the crater. Early in the lecture, the professor cites the Gale Crater as a reason to continue to study Mars. |
| ✗ | C To describe the goals of the Mars rover Curiosity |
Curiosity is being used to learn more about the Gale Crater, but the focus of the lecture is not Curiosity’s goals. |
| ✗ | D To review the atmospheric conditions of Mars in an effort to track its water loss |
This is mentioned as one of the goals of scientists studying the Gale Crater, but this is not the main focus of the lecture. |
|
What does the professor imply about the Mars rover Curiosity? |
Inference. Curiosity is the rover that is currently taking samples from and exploring the Gale Crater. |
|
| ✗ | A It took the first images of Mars’s surface. |
This idea is not mentioned in the lecture. |
| ✗ | B It uses both solar and wind energy. |
The power source of Curiosity is not mentioned in the lecture. |
| ✗ | C It landed a great distance away from the Gale Crater. |
On the contrary, the professor said that Curiosity landed within the Gale Crater. |
| ✓ | D It has the ability to take mineral samples. |
Correct. The professor notes that Curiosity is “taking samples and pictures.” Those samples are later described as being used for mineral analysis.The implication is that Curiosity must be capable of taking mineral samples. |
|
Why is the image of the Gale Crater that the professor displays color-coded? |
Detail. The professor states that it has been color-coded to make it easier for the students to see the different elevations of the crater and the mountain. |
|
| ✗ | A To illustrate that Mount Sharp is taller than any mountain on Earth |
Nothing stated in the lecture supports this idea. |
| ✗ | B To compensate for the poor quality of images sent by Curiosity |
The professor never mentions anything about the quality of images sent by Curiosity. |
| ✓ | C To indicate more clearly what areas of the crater are at a high elevation and what areas are at a low elevation |
Correct. The professor says that “it is easier to see the different elevations using this color-coded map.” |
| ✗ | D To prove that the crater was formed by a meteor impact |
The professor does not claim that the color-coding is related to how the crater was formed. |
|
Why does the professor mention the composition of Mount Sharp? |
Organization. The professor states that Mount Sharp has base consisting of clay and an upper layer consisting of oxygen and sulfur-containing minerals. |
|
| ✗ | A To explain how craters are formed |
The professor doesn’t talk about craters in general. His lecture is about the Gale Crater specifically. |
| ✓ | B To provide evidence to support theories about how it was created |
Correct. Because the bottom layer is clay, it is theorized that there was an ancient lake in that location. The oxygen and sulfur-containing minerals suggest that dirt and rocks were later swept in by wind after the lake dried up. |
| ✗ | C To explain that clay is uncommon in mountains that are not formed from ancient lakes |
This idea is not mentioned in the lecture. |
| ✗ | D To imply that Mount Sharp was formed at the same time as the Gale Crater |
On the contrary, the professor states that the crater was possibly filled by an ancient lake at first, and that the mountain probably developed later. |
|
Why does the professor believe that there may have once been water on Mars? Choose 2 answers. |
Detail. The professor mentions that the Gale Crater was believed to be filled by a lake at one point, and that what appear to be ancient river beds are still present on the higher elevations of Mount Sharp. |
|
| ✓ | a The clay sediment at the base of Mount Sharp could have come from an ancient lake bed. |
Correct. A theorized ancient lake would imply that water was present on Mars at that time. |
| ✓ | b Some of the minerals on Mount Sharp can probably only be formed in the presence of running water. |
Correct. The professor notes this, and adds that there are also what appear to be ancient river and stream beds on the mountain. |
| ✗ | c The atmosphere of Mars contains traces of water. |
According to the professor, the atmosphere of Mars still needs to be studied. He does not discuss the composition of Mars’s atmosphere. |
| ✗ | d Curiosity has found water molecules embedded in rocks within the Gale Crater. |
This is idea is not mentioned in the lecture. |
Narrator: Listen again to part of the lecture. Then answer the question.
Male Student: Why does all this ancient history matter? I mean, shouldn’t we be studying the Earth and not some distant planet?
Professor: Oh, there’s lots we can learn from this.
Narrator: What does the professor imply when he says this:
Professor: Oh, there’s lots we can learn from this.
|
Inference. The professor seems excited about the idea of what studying the Gale Crater might reveal. |
||
| ✗ | A The student should be paying more attention to the lecture than he is. |
The professor is not criticizing the student. He is answering the student’s question. |
| ✗ | B The push to explore other worlds has directly led to an improvement in technology on Earth. |
The professor does not mention or imply this idea. |
| ✗ | C Without continuing to push the boundaries of knowledge, scientific progress will decline. |
The professor does not mention or imply this idea. |
| ✓ | D Understanding the history of Mars may help reveal aspects of the Earth’s history. |
Correct. The professor goes on to give an example in which hypothetical life on Mars might lead to information about how life on Earth began. |