ACT science practice test 53

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


The moon is the earth's only natural satellite and is the fifth-largest moon in the solar system. Believed to be around 4.5 billion years old, the moon was a deity worshipped by ancient civilizations and the first object in the solar system besides Earth that human beings set foot on. It has played a special role in human history, yet despite its ubiquity, the origin of this celestial body remains surrounded by mystery. Theories about the origin of the moon have long been debated among scientists. The following are summaries of the most recent major theories of moon formation. The first three theories are known as the Big Three and represent the predominant ideas before the mid-1970s. The fourth theory represents the most recent school of thought, developed in light of evidence gained from the Apollo space program.

Theory 1: Fission

The moon was spun off from the earth when the planet was young and rotating rapidly on its axis. The empty space the moon left behind became the Pacific Ocean basin.

Theory 2: Capture

The moon formed elsewhere in the universe. At some point, it came near enough to be affected by the earth's gravitational field. The moon was pulled into permanent orbit by the earth's gravity.

Theory 3: Coaccretion

The earth and moon and all other bodies of the solar system condensed independently out of the huge cloud of cold gases and solid particles that constituted the primordial solar nebula. The moon then fell into orbit around the earth.

Theory 4: Giant Impact

The earth was struck by a body about the size of Mars very early in its history. A ring of debris from the impact containing primarily Earth materials and some materials from the impacting object eventually coalesced to form the moon.

1. In which of the theories would the rocks on the moon NOT necessarily bear any similarity to the rocks on the earth?

A. Fission
B. Capture
C. Both fission and coaccretion
D. Both capture and fission

2. In which two of the theories would the rocks on the moon be nearly identical to those on the earth?

A. Capture and fission
B. Capture and coaccretion
C. Coaccretion and fission
D. Giant impact and capture

3. Which of the following statements would best support the argument of a proponent of the capture theory?

A. Planets are incredibly small compared to the vastness of space.
B. Jupiter and Saturn (the giant gas planets) have captured moons.
C. The moon and the earth have the same oxygen isotope composition.
D. The moon does not have a regular-size core.

4. The Big Three theories have cleverly been dubbed the Daughter theory, the Sister theory, and the Spouse theory by scientists who compared the relationship of the moon and the earth to familial relationships. Based on the information in the passage, which of the following would most accurately associate the theories to their nickname: Daughter, Sister, and Spouse?

A. Fission, coaccretion, and capture
B. Capture, fission, and coaccretion
C. Capture, coaccretion, and fission
D. Fission, capture, and coaccretion

5. The following description of the formation of the moon is from a children's radio program in the 1930s. Which of the four moon theories does this seem to illustrate?

Once upon a time-a billion or so years ago-when the earth was still young-a remarkable romance developed between the earth and the sun-according to some of our ablest scientists.… In those days, the earth was a spirited maiden who danced about the princely sun, was charmed by him, yielded to his attraction, and became his bride.… The sun's attraction raised great tides upon the earth's surface… the huge crest of a bulge broke away with such momentum that it could not return to the body of Mother Earth. And this is the way the moon was born!

A. Fission
B. Capture
C. Condensation
D. Giant impact

6. The fission theory is refuted by which of the following pieces of evidence?

A. The moon lacks a large core.
B. There is a striking similarity between the oxygen isotopes present on the earth and those on the moon.
C. Studies of isotopes found in rocks put the age of the earth and moon at 4.5 billion years.
D. The Pacific Ocean basin was formed 70 million years ago.

7. The moon's crust is thinner on the side nearest the earth. Scientists believe that this is because the moon was close to the earth when it formed. As the moon's mantle cooled, the earth's gravitational field pulled slightly more mantle closer to the planet before it "set." A thicker mantle made for a thinner crust on the side nearest the earth. This piece of evidence contradicts the capture theory because:

A. in the capture theory, the moon broke off from the earth.
B. in the capture theory, the moon formed close to the earth.
C. in the capture theory, the moon formed in another part of the solar system.
D. this piece of evidence supports the coaccretion theory.

8. The evidence that rock samples from the moon match rocks from the earth's crust and mantle but bear no resemblance to the earth's interior rock refutes all of the following theories except:

A. fission.
B. capture.
C. coaccretion.
D. giant impact.

9. The giant impact theory:

A. is not likely to change with the discovery of new evidence.
B. completely explains the origin of the moon.
C. is unable to account for why the moon is made mostly of rock.
D. is the theory best supported by the most current scientific evidence.

10. Which of the theories is best supported by the evidence that the earth and moon are both 4.5 billion years old and provide isotopic evidence that indicates they were formed in the same "neighborhood" of the solar system?

A. Fission
B. Capture
C. Coaccretion
D. Giant impact

11. A fifth theory of moon formation, called the colliding planetesimals theory, exists. In this theory, an asteroid-like chunk of rock orbiting the sun collided with an asteroid-like chunk of rock orbiting the earth. The moon then condensed from the debris of this collision. This theory would be weakened by which of the following pieces of evidence?

A. Moon rock matches the rock from the earth's crust and mantle.
B. The moon's crust is thinner on the side nearest the earth.
C. The moon is made of mostly rock.
D. Isotopes indicate that the earth and moon formed in the same area of the solar system.