The Giant Impact theory of the origin of Earth’s Moon is currently the most widely accepted, yet it violates the central premise of the scientific method.
a) What is the difference between a scientific and non-scientific theory?
b) Explain why the giant impact theory can be called “unscientific”.
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In the early history of our solar system, there was a period of very heavy bombardment that both the Earth and the Moon suffered through.
(a) Were the maria on the Moon formed before or after this period of time?
(b) Explain how you can determine this based on what we see today on the Moon.
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The geology of the Moon tells us that it was once geologically active, with lava flows on the surface.
a) (2 pts) Did this period of activity occur before or after the period of extensive bombardment in our solar system’s history?
b) (4 pts) Explain your answer to part (a).
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A satellite photograph of a strange new planetary surface looks like the figure below.
a) (3 pts) Which part of the planetary surface is the youngest (A, B, C)?
b) (3 pts) Which part of the planetary surface is the oldest (A, B, C)?
c) (6 pts) Explain your answer to parts (a) and (b) above.
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The Moon has the same isotope fingerprint as Earth, but it lacks volatiles. This implies two things about the Moon’s origin that any lunar formation theory must explain. What two things?
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The lunar maria were originally thought to be oceans of water, but telescopic observations soon revealed the harsh reality that they are plains of dried lava. 1-2 sentences should be a sufficient answer for each part of this question.
a) (6 pts) What purely observational evidence do we have that tells us the lunar maria are geologically younger (they solidified later) than the lunar highlands?
b) (6 pts) What direct physical evidence do we have that the maria are younger?
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Even without directly sampling the surface of Mercury, we can tell purely by observation what is its age relative to the more densely cratered lunar highlands.
a) (4 pts) Is the surface of Mercury (older than, younger than, same age as) the lunar highlands?
b) (8 pts) Explain your answer to part (a).
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Perhaps the most widely accepted theory of the Moon’s origin is the so-called “giant impact” theory that a Mars-sized object crashed into the Earth very soon after Earth formed.
a) (6 pts) How does the giant impact theory explain the isotope fingerprint of the Moon compared to the Earth?
b) (6 pts) Why don’t many scientists readily accept this theory?
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The controversy over the origin of lunar craters wasn’t definitively resolved until evidence was brought back to settle the case by the Apollo lunar lander missions.
a) (6 pts) How do craters on the moon differ observationally from volcanic craters on the Earth?
b) (6 pts) What direct physical evidence did Apollo bring back to confirm that the craters on the Moon are not caused by volcanism?
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What is the composition of the soil and the lunar maria and the lunar highlands, and what does the difference between the two soil types tell us about the geological history of these two different parts of the Moon?
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We know that the Earth’s Moon has an isotope fingerprint that is identical to that of the Earth, yet it lacks volatiles, unlike the Earth. The Moon also seems to lack a dense iron core, unlike the Earth, so the overall density of the Moon is lower than that of the Earth.
a) (3 pts) Briefly explain what a volatile element is.
b) (5 pts) What does the lack of volatiles on Earth’s Moon imply about its formation conditions?
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We know that the Earth’s Moon has an isotope fingerprint that is identical to that of the Earth, yet it also lacks volatiles, unlike the Earth. The Moon also seems to lack a dense iron core, unlike the Earth, so the overall density of the Moon is lower than that of the Earth. The fission hypothesis for the origin of Earth’s Moon says that the Earth was spinning so rapidly early in its history that a part of the equatorial region broke off and sailed into orbit, a process that did not involve any heating of the material. Name and explain two reasons why the “giant impact” theory is preferable to this “fission” theory.
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The Apollo missions to the Moon brought back Moon rocks and found that they have roughly the same composition as the Earth’s mantle.
a) (8 pts) How does this evidence support the “fission” hypothesis for the origin of the Earth’s Moon? Explain (start by explaining what the fission hypothesis is in 1-2 sentences).
b) (4 pts) Why don’t most scientists accept the “fission” hypothesis as the most plausible explanation for the origin of the Earth’s Moon?
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The crater retention age of the Earth’s surface is much lower (in the other words, the surface of the Earth has far fewer craters) than either the lunar maria or the lunar highlands.
a) (6 pts) Explain the concept of “crater retention age”, and as part of your explanation, state whether the statement above implies that the Earth’s surface is older than or younger than the lunar maria and the lunar highlands.
b) (6 pts) What is happening within the Earth that makes Earth’s crater retention age so different from that the the lunar maria and highlands?
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Various theories for the origin of the Earth’s Moon have been discarded by scientists as these theories have run into insurmountable logical problems.
a) (4 pts) The Co-Accretion theory claims that the Earth and Moon formed together from the same clump of material in the solar nebula. What evidence leads us to discount this theory? Explain.
b) (4 pts) The Capture theory claims that the Moon was a wandering planetesimal that was captured into orbit around Earth. What is it about the composition of the Earth and Moon that leads us to discount this theory? Explain.
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The Co-Accretion theory of the Origin of the Moon has been fairly popular among some scientists in the past, though it is now no longer widely viewed as correct. Explain in detail one fact that this theory proves correctly and one fact that this theory does not prove correctly.
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The Fission hypothesis for the origin of the Moon states that the Earth was spinning around so rapidly soon after its formation that parts of it were flung out into space, where they subsequently coalesced to form the Moon. The Giant Impact theory, on the other hand, states that the Earth was struck by a large impactor, knocking a chunk of Earth's mantle into orbit.
a) (7 pts) The Earth and the Moon have isotope "fingerprints" that are virtually identical when the abundances of "tough" elements are compared (these are elements that can withstand heat, unlike fragile "volatile" elements). Explain how this fact supports both theories.
b) (7 pts) The Earth and Moon have different abundances of fragile "volatile" elements. Which theory predicts that the Moon should have a different abundance of volatile elements? Should the Moon's abundance be larger or smaller than the Earth, according to this theory? Explain your answer.
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Explain how Astronomers believe ice could have survived on the surface of the Moon for all these billions of years.
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The giant impact theory for the origin of the Moon is the most widely believed theory for the origin of Earth's Moon because of its ability to explain several interesting features of the Moon's composition.
a) (8 pts) Explain how the giant impact theory successfully explains the difference in the relative size of the metallic core for the Earth and Moon and the similarity between the isotope fingerprint of the Earth and Moon.
b) (6 pts) Explain how the giant impact theory successfully explains the difference in the amount of volatiles found in the Earth and Moon.
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Explain how we know that the cratering rate on the Moon hasn't been constant over time.
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The capture hypothesis for the origin of our solar system states that the Sun captured wandering interstellar bodies that subsequently fell into orbit around it to form our solar system.
a) (8 pts) Name and briefly explain two reasons why this hypothesis is not accepted by most Astronomers today (one dealing with orbits, the other with probability).
b) (6 pts) A similar capture theory is sometimes used to explain the origin of the Earth's Moon. An isotope fingerprint measures the relative abundances of several different isotopes (such as Oxygen-16, Oxygen-17, Oxygen-18, etc) in an object. How do the isotope fingerprints of the Earth and Moon compare, and how is this evidence used to contradict the capture idea?
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Two popular theories for the origin of Earth's Moon are the "fission" and the "giant impact" theory. Explain how each theory is supported (or refuted) by the abundance of volatiles on the Earth and Moon, and explain how each theory is supported (or refuted) by the isotope fingerprints of the Earth and Moon.
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One theory for the origin of Earth's moon is the fission hypothesis, which says that early on, the Earth was spinning so rapidly, pieces of it flew off from the equatorial region, and these fragments subsequently coalesced in orbit around the Earth to form our moon.
a) (7 pts) Name and explain two pieces of evidence that support the fission theory.
b) (7 pts) Name and explain two pieces of evidence that contradict the fission theory.
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The maria and the highlands on the Moon offer Astronomers some insight into the Moon's history, particularly when one examines the cratering patterns in each.
a) (8 pts) Explain why the maria are typically found at low elevation and why the maria terrain looks so different from the highlands terrain.
b) (6 pts) Explain why, prior to returning with samples for radioactive dating, many Astronomers predicted that the solidification age of the lunar maria would be about a tenth or less compared to the solidification age of the highlands.
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The Giant Impact theory for the origin of the Earth's moon is the most popular among Astronomers today, though some argue that it is philosophically flawed.
a) (4 pts) Name and briefly explain two pieces of evidence that support the Giant Impact theory.
b) (4 pts) Some argue that the Giant Impact theory is not falsifiable. Explain why scientific theories should be falsifiable, as discussed in the Pine reading.