Water on Mars - TOEFL Reading Practice Test with Answer Key

When preparing for the TOEFL iBT® exam, you can greatly benefit from practicing tests. Not only do they boost your chances of success on exam day, but also maximize your score potential. Engaging in such assessments for the TOEFL iBT® Reading section will acquaint you with the exam's format and also enhance the essential skills needed to ace it.

So, let's kickstart your TOEFL iBT® preparation with the Reading Practice Test paper on the topic- 'Water on Mars.' This test will enhance your ability to comprehend complex texts effectively and refine your reading skills for D-day.

Reading Instructions

• You will be given 15 minutes to read the following passage and answer all 9 questions following it.
• Most questions are worth 1 point, but the last question is worth more. The directions indicate how many points you will receive for that specific question. 
• The specific paragraphs have been provided alongside the question for quick solutions and better understanding.
• Some questions include a word or phrase that is highlighted in the question as well as in the paragraph for quick reference. 

Water on Mars

Photographic evidence indicates that there was a significant presence of liquid water on Mars' surface in the past. This evidence reveals two distinct types of flow patterns: runoff channels and outflow channels. The runoff channels are primarily located in the southern highlands and comprise extensive systems of interconnected and twisting channels, sometimes spanning hundreds of kilometers. These channels appear to merge into larger and wider channels, bearing a striking resemblance to Earth's river systems. Geologists theorize that these runoff channels are remnants of ancient rivers that once transported rainfall from Martian mountains to valleys, suggesting a time around 4 billion years ago when Mars had a thicker atmosphere, warmer surface temperatures, and widespread liquid water.

Outflow channels are most likely relics of significant flooding that occurred on Mars in the distant past. These channels are limited to equatorial regions and typically do not create extensive interconnected networks. Instead, they likely represent the pathways through which large amounts of water flowed from the southern highlands to the northern plains. The rapid flow of water during these flash floods probably created the peculiar teardrop-shaped "islands," similar to those found in wet beach sand during low tide, near the ends of these channels on the plains. Based on the dimensions of these channels, the flow rates must have been extremely high, possibly reaching a hundred times more than the 105 tons per second carried by the Amazon River. The formation of these outflow channels can be attributed to flooding that occurred around 3 billion years ago, coinciding with the formation of the northern volcanic plains.

Some scientists hypothesize that Mars may have experienced a prolonged initial phase where it had rivers, lakes, and possibly even oceans on its surface. According to a 2003 Mars Global Surveyor image, experts believe they have identified a delta—a fan-shaped system of channels and sediments where a river once flowed into a larger water body, such as a lake within a crater in the southern highlands. Other researchers take this idea further, proposing that the data indicates significant open water areas existed on early Mars. An image generated by a computer, focusing on the Martian north polar region, illustrates the potential extent of what could have been an ancient ocean covering a large portion of the northern lowlands. The Hellas Basin, spanning about 3,000 kilometers and featuring a floor nearly 9 kilometers below the basin's edge, is also considered a possible site of an ancient Martian sea.

These concepts continue to spark debate. Advocates highlight features like the terraced "beaches" captured in an image, suggesting they might have formed as a lake or ocean dried up and the shoreline moved back. Conversely, critics argue that these terraces could have resulted from geological processes, possibly linked to forces that lowered the Northern Hemisphere significantly compared to the southern part of Mars, thereby unrelated to water on Mars. Additionally, data from the Mars Global Surveyor in 2003 suggest a scarcity of carbonate rock layers on the Martian surface—layers containing carbon and oxygen compounds that would be abundant in an ancient ocean. Their absence reinforces the notion of a cold, arid Mars that never underwent the prolonged warm period necessary for lake and ocean formation. Nevertheless, recent data hint that certain regions of Mars did experience extended periods in the past when liquid water was present on its surface.

Apart from some small-scale gullies discovered since 2000, which are not definitive proof, astronomers lack direct confirmation of liquid water on Mars' surface today, and the level of water vapor in the Martian atmosphere is minimal. However, disregarding the unverified clues of ancient oceans, the vastness of the outflow channels indicates a significant amount of water was present on Mars in earlier times. The question arises: what happened to all this water? One possibility is that nearly all of Mars' water is currently trapped in the permafrost layer beneath the surface, with additional water held in the planet's polar caps.

Directions: Once you have read the passage, answer the following questions.

Paragraph 1

Photographic evidence indicates that there was a significant presence of liquid water on Mars' surface in the past. This evidence reveals two distinct types of flow patterns: runoff channels and outflow channels. The runoff channels are primarily located in the southern highlands and comprise extensive systems of interconnected and twisting channels, sometimes spanning hundreds of kilometers. These channels appear to merge into larger and wider channels, bearing a striking resemblance to Earth's river systems. Geologists theorize that these runoff channels are remnants of ancient rivers that once transported rainfall from Martian mountains to valleys, suggesting a time around 4 billion years ago when Mars had a thicker atmosphere, warmer surface temperatures, and widespread liquid water.

1. The word “merge” in the passage is most similar in meaning to
   1. expand
   2. Separate
   3. straighten out
   4. combine

Paragraph 2

Outflow channels are most likely relics of significant flooding that occurred on Mars in the distant past. These channels are limited to equatorial regions and typically do not create extensive interconnected networks. Instead, they likely represent the pathways through which large amounts of water flowed from the southern highlands to the northern plains. The rapid flow of water during these flash floods probably created the peculiar teardrop-shaped "islands," similar to those found in wet beach sand during low tide, near the ends of these channels on the plains. Based on the dimensions of these channels, the flow rates must have been extremely high, possibly reaching a hundred times more than the 105 tons per second carried by the Amazon River. The formation of these outflow channels can be attributed to flooding that occurred around 3 billion years ago, coinciding with the formation of the northern volcanic plains.

1. The word “relics” in the passage is most similar in meaning to
   1. remains
   2. sites
   3. requirements
   4. sources

1. Why does the author mention that 105 tons of water flow through the Amazon river per second in paragraph 2?
   1. To highlight the considerable volume of water that may have passed through Mars' outflow channels.
   2. To show the information scientists used to calculate the age of Mars' outflow channels.
   3. To suggest that flash floods on Mars might have been forceful enough to create tear-shaped "islands."
   4. To propose that the strength of floodwaters on Mars shaped the northern volcanic plains.

1. According to the passage, everything mentioned below about the outflow channels on Mars is accurate except for one statement:
   1. They were created roughly during the period of volcanic eruptions in the northern plains.
   2. They are limited to specific areas of the Martian surface.
   3. Occasionally, they discharge onto what seem to be former damp sands of tidal beaches.
   4. It is believed that they transported water towards the north from the equatorial zones.

Paragraph 3

Some scientists hypothesize that Mars may have experienced a prolonged initial phase where it had rivers, lakes, and possibly even oceans on its surface. According to a 2003 Mars Global Surveyor image, experts believe they have identified a delta—a fan-shaped system of channels and sediments where a river once flowed into a larger water body, such as a lake within a crater in the southern highlands. Other researchers take this idea further, proposing that the data indicates significant open water areas existed on early Mars. An image generated by a computer, focusing on the Martian north polar region, illustrates the potential extent of what could have been an ancient ocean covering a large portion of the northern lowlands. The Hellas Basin, spanning about 3,000 kilometers and featuring a floor nearly 9 kilometers below the basin's edge, is also considered a possible site of an ancient Martian sea.

1. All inquiries concerning geological features on Mars are addressed in paragraph 3 except for the following:
   1. Identifying regions on Mars that may have previously been ocean-covered.
   2. Determining the location where mission scientists think the river contributing to the delta terminated.
   3. Estimating the number of craters on Mars that mission scientists speculate could have functioned as water-filled lakes.
   4. Identifying the historical period on Mars when some scientists hypothesize the presence of substantial water bodies.

1. The passage suggests that observations of Mars' surface images are seen as evidence that:
   1. the polar regions of Mars were previously more expansive than their current state,
   2. a significant portion of the northern lowlands might have been submerged in the past,
   3. deltas were once prevalent in the Martian scenery,
   4. the configuration of the Hellas Basin has undergone substantial transformations over time.

1. Which inference is supported by the paragraph concerning liquid water on Mars?
   1. Early Martian lakes were probably comparable in size to some present-day Earth lakes.
   2. Any liquid water currently present on Mars' surface is significantly less than what likely existed there previously.
   3. Recent small-scale gullies on Mars offer compelling proof of the past existence of liquid water.
   4. The limited water vapor in Mars' atmosphere indicates the absence of liquid water throughout Mars' history.

Paragraph 4

These concepts continue to spark debate. Advocates highlight features like the terraced "beaches" captured in an image, suggesting they might have formed as a lake or ocean dried up and the shoreline moved back. Conversely, critics argue that these terraces could have resulted from geological processes, possibly linked to forces that lowered the Northern Hemisphere significantly compared to the southern part of Mars, thereby unrelated to water on Mars. Additionally, data from the Mars Global Surveyor in 2003 suggest a scarcity of carbonate rock layers on the Martian surface—layers containing carbon and oxygen compounds that would be abundant in an ancient ocean. Their absence reinforces the notion of a cold, arid Mars that never underwent the prolonged warm period necessary for lake and ocean formation. Nevertheless, recent data hint that certain regions of Mars did experience extended periods in the past when liquid water was present on its surface.

1. As per the paragraph, what is indicated by the 2003 Global Surveyor data regarding Mars?
   1. Mars' ancient oceans had limited amounts of carbon.
   2. Mars' climate might not have been conducive to creating extensive bodies of water.
   3. Some areas of Mars' surface potentially hosted liquid water for extended durations.
   4. The ancient oceans on Mars evaporated during cold and arid periods.

1. Consider the excerpt provided below. The labels (A), (B), (C), and (D) indicate potential insertion points for the following statement. 
   
   These landscape features differ from runoff channels in a number of ways.
   
   Where would the sentence best fit?
   
   Outflow channels are most likely relics of significant flooding that occurred on Mars in the distant past. (A) These channels are limited to equatorial regions and typically do not create extensive interconnected networks. (B) Instead, they likely represent the pathways through which large amounts of water flowed from the southern highlands to the northern plains. (C) The rapid flow of water during these flash floods probably created the peculiar teardrop-shaped "islands," similar to those found in wet beach sand during low tide, near the ends of these channels on the plains. (D) Based on the dimensions of these channels, the flow rates must have been extremely high, possibly reaching a hundred times more than the 105 tons per second carried by the Amazon River. The formation of these outflow channels can be attributed to flooding that occurred around 3 billion years ago, coinciding with the formation of the northern volcanic plains.
   1. A. Choice A
   2. B. Choice B
   3. C. Choice C
   4. D. Choice D

1. Instructions: Below is an introductory sentence for summarizing the passage. You need to choose three answer choices that represent the most significant ideas in the passage to complete the summary. Some answer choices are irrelevant or minor ideas not discussed in the passage. This question carries a weight of 2 points.
   
   There is much debate concerning whether Mars once had water.
   
   Answer Choices
   1. A. Different kinds of images have been utilized to show that a significant portion of Mars' surface displays indications of water flow.
   2. B. The channels for runoff and outflow on Mars are believed to have transported a larger volume of water and created more extensive networks compared to rivers on Earth.
   3. C. The runoff and outflow channels on Mars are notable, distinctive features that imply substantial amounts of liquid water were once present on the planet.
   4. D. While some scientists argue that Mars might have had oceans in the past, others challenge this idea, citing a lack of evidence or proposing alternative interpretations of the evidence.
   5. E. Despite the discovery of numerous gullies on Mars since 2000, many astronomers dismiss them as proof of past liquid water on the planet.
   6. F. Presently, there is scant evidence of liquid water on Mars, and it is believed that all the water that existed on the planet is now frozen beneath its surface.

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Answer Key with Explanation for TOEFL iBT® Reading Passage - Water on Mars

1. Answer: D

Explanation: This is a Vocabulary question. The word "merge" in the passage is most similar in meaning to "combine" (option D). This is because "merge" refers to the action of two or more things coming together to form a single entity or unit. In the context of the passage, the runoff channels on Mars appear to merge into larger and wider channels, indicating that multiple smaller channels combine to form larger ones. Therefore, "combine" best captures the idea of different elements coming together to form a unified whole, which is the essence of "merge" in this context.

2. Answer: A

Explanation:  This is a Vocabulary question. The word "relics" in the passage is most similar in meaning to "remains" (option A). "Relics" refers to objects or elements that are left from the past, often with historical or cultural significance. In the context of the passage, "relics" is used to describe the outflow channels on Mars as remnants of significant flooding that occurred in the distant past. These channels are essentially the remains or remnants of the past flooding events. Therefore, "remains" is the most appropriate synonym for "relics" in this context.

3. Answer: A

Explanation: The author mentions that 105 tons of water flow through the Amazon River per second in paragraph 2 to highlight the considerable volume of water that may have passed through Mars' outflow channels (option A). This comparison is made to emphasize the immense flow rates that would have been necessary to shape the outflow channels on Mars. By mentioning the flow rate of the Amazon River, which is known for its significant water discharge, the author gives readers a tangible comparison to understand the scale of water flow that might have occurred on Mars. Therefore, option A is the correct explanation.

4. Answer: C

Explanation: The statement that is not accurate about the outflow channels on Mars, according to the passage, is (C) Occasionally, they discharge onto what seem to be former damp sands of tidal beaches. This statement is not mentioned in the passage. The passage discusses the outflow channels discharging water from the southern highlands to the northern plains but does not mention them discharging onto former damp sands of tidal beaches. Therefore, option C is the correct answer.

5. Answer: C

Explanation: The statement that is not addressed in paragraph 3 regarding geological features on Mars is (C) Estimating the number of craters on Mars that mission scientists speculate could have functioned as water-filled lakes. Paragraph 3 mainly discusses the identification of regions on Mars that may have been ocean-covered, including the potential presence of deltas and ancient oceans. It also mentions mission scientists identifying a delta where a river once flowed into a larger water body, such as a lake within a crater. However, the paragraph does not specifically mention estimating the number of craters that could have functioned as water-filled lakes. Therefore, option C is the correct answer.

6. Answer: B

Explanation: The passage suggests that observations of Mars' surface images are seen as evidence that (B) a significant portion of the northern lowlands might have been submerged in the past. This is supported by the passage's discussion of images showing potential ancient oceans covering large areas of the northern lowlands. The mention of a delta and the Hellas Basin as possible sites of ancient seas also reinforces the idea that substantial portions of the northern lowlands could have been underwater in the past. Therefore, option B is the correct answer.

7. Answer: B

Explanation: The inference supported by the paragraph concerning liquid water on Mars is (B) Any liquid water currently present on Mars' surface is significantly less than what likely existed there previously. This inference is supported by the passage's discussion of ancient oceans, rivers, and lakes on Mars, suggesting that significant amounts of liquid water were present in the past. However, the passage also mentions that there is very little evidence of liquid water on Mars today, with astronomers lacking direct confirmation of it on the planet's surface. The minimal level of water vapor in Mars' atmosphere further reinforces the idea that any liquid water currently present on Mars is much less than what likely existed there previously. Therefore, option B is the correct answer.

8. Answer: B

Explanation: The paragraph indicates that the 2003 Mars Global Surveyor data suggest (B) Mars' climate might not have been conducive to creating extensive bodies of water.

This inference is supported by the passage's mention of the scarcity of carbonate rock layers on Mars' surface, which are typically abundant in ancient oceans. The absence of these layers suggests that Mars may have been cold and arid for extended periods, which would not be conducive to the formation of extensive bodies of water such as ancient oceans. Therefore, option B is the correct answer.

9. Answer: A

Explanation: The sentence "These landscape features differ from runoff channels in a number of ways" would best fit before or after choice A. This is because choice A introduces the topic of outflow channels and their differences from runoff channels, making it the most appropriate location for the sentence that discusses these differences. Placing the sentence before choice A would introduce the comparison, while placing it after choice A would reinforce the idea presented in choice A. Therefore, the answer is A.

10. Answer: C,D,F

Explanation: This is a Prose Summary question. It is completed correctly below.

There is much debate concerning whether Mars once had water.

Answer Choices

A. Different kinds of images have been utilized to show that a significant portion of Mars' surface displays indications of water flow.

B. The channels for runoff and outflow on Mars are believed to have transported a larger volume of water and created more extensive networks compared to rivers on Earth.

C. The runoff and outflow channels on Mars are notable, distinctive features that imply substantial amounts of liquid water were once present on the planet.

D. While some scientists argue that Mars might have had oceans in the past, others challenge this idea, citing a lack of evidence or proposing alternative interpretations of the evidence.

E. Despite the discovery of numerous gullies on Mars since 2000, many astronomers dismiss them as proof of past liquid water on the planet.

F. Presently, there is scant evidence of liquid water on Mars, and it is believed that all the water that existed on the planet is now frozen beneath its surface.

Correct Choices

Choice C"The runoff and outflow channels on Mars are notable, distinctive features that imply substantial amounts of liquid water were once present on the planet" summarizes a key point in the passage. It highlights the significance of the runoff and outflow channels as evidence of past liquid water on Mars.

Choice D "While some scientists argue that Mars might have had oceans in the past, others challenge this idea, citing a lack of evidence or proposing alternative interpretations of the evidence" encapsulates the ongoing debate mentioned in the passage about the existence of oceans on Mars in the past.

Choice F "Presently, there is scant evidence of liquid water on Mars, and it is believed that all the water that existed on the planet is now frozen beneath its surface" summarizes the passage's conclusion regarding the current state of water on Mars and the belief that any water present is now frozen underground.

Incorrect Choices

Choice A Different kinds of images have been utilized to show that a significant portion of Mars' surface displays indications of water flow. While this choice mentions images showing indications of water flow on Mars, it does not directly address the debate about whether Mars once had water or the arguments and evidence presented regarding this debate.

Choice B The channels for runoff and outflow on Mars are believed to have transported a larger volume of water and created more extensive networks compared to rivers on Earth. This choice discusses the characteristics of the channels on Mars but does not directly address the debate about whether Mars once had water or the arguments and evidence presented regarding this debate.

Choice E Despite the discovery of numerous gullies on Mars since 2000, many astronomers dismiss them as proof of past liquid water on the planet. While this choice mentions astronomers dismissing gullies as proof of past liquid water, it does not directly address the debate about whether Mars once had water or the arguments and evidence presented regarding this debate.

What did you think of that Reading passage? Share with us how many answers you guessed correctly in the comments section below and continue your preparation with some more TOEFL Practice tests!

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