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Updated through Friday, November 20.

(112)

Briefly explain the concept of sources and sinks in the Carbon cycle. Give at least two examples of sources and two examples of sinks.

(113)

What is the ozone layer, and why is it important for life on Earth? Explain how the production of Chloroflourocarbons (CFC's) results in the partial destruction of Earth's ozone layer.

(114)

Read the EPA's web page about ozone at http://ozonewatch.gsfc.nasa.gov/facts/hole.html to answer the following question: Briefly explain two reasons (one having to do with wind patterns and one having to do with ice clouds) why the ozone depletion largely occurs over the Antarctic each year rather than uniformly in the rest of the Earth's atmosphere. (TQ)

The following four Thought Questions come from the Scientific American article "The Origins of Water on Earth" (September 2003).

(115)

How do we know that water has been present on the Earth since shortly after its formation? (TQ)

(116)

Briefly explain two possible ways early Earth's water could've been "lost" and not become a permanent part of Earth's oceans. (TQ)

(117)

Explain the evidence from recently-observed comets (such as Halley) that implies most of Earth's water probably did not come from comets. (TQ)

(118)

What is the Faint Sun paradox and how has it been "resolved" by our atmosphere? (we covered this in lecture as well) (TQ)

(119)

Argon gas is called a "tracer" because it is one of the few gases in our atmosphere that maintains its original abundance from the original (primitive) atmosphere to the modern (secondary) atmosphere. What two properties of Argon gas make this possible? Explain why each one is important.

(120)

Explain how the maria on the Moon formed and why their appearance differs from that of the lunar highlands.

(121)

Explain why the surface of the moon maintains a record of the era of early bombardment (the first half-billion years after the formation of the planets) while Earth's surface does not.

(122)

Explain why the Moon lacks a magnetic field. Explain also why it lacks an atmosphere.

(123)

Explain the capture theory of the Moon's formation in a sentence or two. Explain why this theory has problems explaining the mass ratio of the Moon compared to the Earth and the isotope fingerprints of the Earth and the Moon.

(124)

Explain the Co-Creation theory of the Moon's formation in a sentence or two. Explain why this theory has problems explaining the rock/metal ratio in the Moon and the lack of volatiles in the Moon compared to the Earth.

(125)

What are volatiles? The Moon has a lower abundance of volatiles than the Earth's mantle. What does this fact imply about the history of the material that formed the Moon, compared to the history of the material that formed the Earth's mantle?

(126)

Explain the Fission theory of the Moon's formation in a sentence or two. Explain why this theory successfully predicts the rock/metal ratio in the Moon and the isotope fingerprint similarity between Earth and Moon.

(127)

Why does the Fission theory have trouble explaining the difference in abundance of volatiles in the Earth and Moon? Also, explain how the current (relatively slow) rotation of the Earth is a problem for the Fission hypothesis.

(128)

Explain the Giant Impact theory of the Moon's formation in a sentence or two. Explain why this theory successfully predicts the rock/metal ratio in the Moon, the isotope fingerprint similarity between Earth and Moon, and the relative lack of volatiles on the Moon compared to the Earth.

(129)

Some scientists are wary of the Giant Impact theory because it does not really qualify as a falsifiable theory. Explain why. Explain what falsifiable means and why a scientific theory should be falsifiable (you may wish to revisit relevant sections of the Philosophy and the Scientific Method reading from the Physics 20073 home page).

The following five Thought Questions can be answered by reading the Scientific American article "Mercury: The Forgotten Planet" from the 2003 special edition on the solar system. For instructions on how to electronically download pdf versions of Scientific American articles, please see the previous study guide.

(130)

Explain the reasoning that leads us to believe that a large fraction of Mercury's mass consists of iron. (TQ)

(131)

Explain why we think substantial quantities of sulfur may be present in the interior of Mercury (this has to do with its magnetic field). (TQ)

(132)

What is the Mercurian Grid, and how do we think it formed? (TQ)

(133)

Why are craters on Mercury typically larger than craters found on the Earth's Moon? (TQ)

(134)

Explain two sources of the gases in Mercury's tenuous atmosphere. (TQ)

(135)

What does it mean to say that we are communicating with extraterrestrials already? What do our signals sound like at various distances from the Earth? Explain.

(136)

Why do radio wavelengths work as the best way to communicate with potential extraterrestrials?

(137)

What is the Fermi paradox, and what is one possible response?

(138)

What is an example of an observation Galileo made to show that objects in the Universe are not static like paintings on the inside of cathedrals?

(139)

What arguments can you make that evolution is very unlikely to result in intelligence? What is an emergent property? Explain this concept in general, and then give one example.

(140)

How and why does the lifetime of a civilization relate to the probability that we are not alone?

(141)

One of the three theories attempting to explain Mercury's large core relative to the other terrestrial planets involves evaporation of the mantle. Briefly describe this theory and then name and explain what observation we could make about the crust via spacecraft (the Messenger mission) that would confirm this theory.

(142)

Another theory for Mercury's core is giant impact. Briefly describe this theory and then name and explain what observation we could make about the crust via spacecraft that would confirm this theory.

(143)

Another theory for Mercury's core is simple condensation. Briefly describe this theory and then name and explain what observation we could make about the crust via spacecraft that would confirm this theory.

(144)

Explain why Mercury undergoes tidal heating due to its unusual orbit around the Sun.

(145)

Why does Venus lack a magnetic field?

(146)

Explain how the craters on Venus differ from craters found on Earth in two parts: First, explain how we estimate the solidification age of Venus' surface to be about 500 million years. Second, craters on Venus all tend to have a pristine appearance compared to craters on the Earth. Explain why this difference exists.

(147)

Explain the evidence that implies Venus suffered some sort of catastrophic event about 500 million years ago that essentially resurfaced the planet.

(148)

Describe the mechanism (besides giant impact) that may have resulted in this resurfacing of Venus referred to in question 147 (melting cycle).

(149)

Why did some observers long ago think that Venus has a moon? What was the hypothetical "Neith" as it relates to Venus? What is the currently accepted explanation of "observations" of Venus' moon? (The Nine Planets website is a good place to go for this, look under the heading "Hypothetical Planets") (TQ)

(150)

Read http://www.physics.upenn.edu/nineplanets/venus.html and briefly explain why no small craters exist on Venus. (TQ)

(151)

One possible explanation for the lack of water on Venus is that Venus never had much water to begin with, compared to the Earth. Explain two reasons why this explanation is not plausible.

(152)

If Venus had twice as much Argon today as the Earth, what would we then assume about Venus' original atmosphere? Explain.

(153)

Although Venus started with an atmosphere that was probably very similar in mass and composition compared with the Earth, various differences between Earth and Venus led to a gradual loss of water vapor on Venus, combined with an enormous increase in the carbon dioxide content. Describe the positive feedback mechanism (Runaway Greenhouse Effect) by which water is lost and the atmosphere thickened.

(154)

Name and briefly explain the significance of three important differences between Venus and the Earth that led Venus to undergo the Runaway Greenhouse process while Earth did not.

(155)

What is Deuterium? What is heavy water? What is the difference between heavy water and normal water? An alternative explanation for the lack of water on Venus is that the water was absorbed into the crust somehow and now resides below the surface in aquifers or underground lakes. Explain how the heavy/light water ratio tends to argue against this hypothesis.

(156)

Read this article and describe the evidence that Mars may have once experienced plate tectonics just like the Earth. Specifically, describe what the evidence is, exactly, then explain why that evidence points to the existence of a magnetic field (describe how a magnetic field helps create such a feature in the rocks). For more on this magnetic phenomenon, including a helpful diagram, you can read the Wikipedia article on plate tectonics. (TQ)

(157)

Explore the following web site from NASA's Goddard Space Flight Center about the Martian meteorites:http://www-curator.jsc.nasa.gov/antmet/marsmets/index.cfm. Based on the information found here, answer the following: What conclusive evidence shows that these meteorites are from Mars? Why aren't these meteorites red like the Martian surface soil? (TQ)

(158)

Why do we think Mars has little significant internal heating (compared to Earth and Venus)? Why doesn't Mars have a significant magnetic field?

(159)

Name and briefly explain two reasons why Olympus Mons on Mars is so much larger than any mountain on the Earth.

(160)

Explain what "dynamic heating" is and how Jupiter is likely responsible for the formation of the asteroid belt and also the relatively small size of Mars.

(161)

Explain the mechanism behind the global dust storms that periodically cover the Martian surface. Why don't similar storms happen on Earth?

(162)

Name and explain the physical, observed evidence that tells us Mars once had an Earthlike atmosphere at some point in its past.

(163)

The Martian atmosphere today has about 1% of the mass of Earth's atmosphere. Explain how Argon reconstruction seems to imply the original mass of the Martian atmosphere was also about 1% of the mass of the Earth's atmosphere.

(164)

How does the 38-Ar/36-Ar ratio on Mars compare to Earth? Why does this ratio argue that Argon reconstruction is probably not correct to apply on Mars as in question 163?

(165)

Explain the "freeze out" theory that may have led to the loss of the Martian atmosphere. Specifically, explain what triggered the beginning of this process and how this process gradually leads to a colder atmosphere which causes the water to condense into solid ice on (or under) the surface (the "freezing out" part).

(166)

How does the "impact erosion" (IE) theory propose to explain the loss of the Martian atmosphere? Why does the IE process occur on Mars and not on Earth, according to the theory (two reasons)?

(167)

How does the "solar wind stripping" theory propose to explain the loss of the Martian atmosphere? Why does Mars presumably suffer from this effect while Earth does not?

(168)

Explain why the freeze out theory doesn't successfully explain the Argon isotopes on Mars mentioned in 164 while impact erosion and solar wind stripping do explain it.

(169)

Explain the origin of meteor showers. Why do meteor showers occur at the same times each year?

(170)

What is the radiant of a meteor shower? Explain how meteor showers are named.

(171)

Use a simple diagram of the Earth and its orbit around the Sun (a top view) to help explain why the best time to observe a meteor shower is in the few hours before dawn.

(172)

Why is Jupiter's magnetic field so much stronger than Earth's? As part of your answer, explain why much of the Hydrogen in Jupiter is in liquid or molten form (in which it behaves like a metal).

(173)

Explain the origin of the belts and zones on the visible surface of Jupiter.

(174)

Although Io is similar in many ways to Earth's Moon, it orbits much more quickly around Jupiter (once every 40 hours as opposed to the Moon's 27.3 day sidereal period). Use the equation of orbital velocity to help explain why.

(175)

Visit http://www.nineplanets.org/jupiter.html and describe what is thought to be the main source of Jupiter's internal heat. (TQ)

(176)

From the same web site mentioned above, what is the origin of Jupiter's faint ring system? In other words, where do the rocky particles come from that make up this thin, dark ring? (TQ)

(177)

Seen here and explained more fully here are the aurorae on Jupiter. What is the origin of the auroral ovals, streaks and dots on Jupiter? (TQ)

The next two thought questions are from a series of SETI-related articles found at the Sky and Telescope magazine website: http://skytonight.com/resources/seti

(178)

From the article "SETI Searches Today": What are two reasons to search for SETI signals near the 21-cm wavelength at which Hydrogen atoms naturally emit light? (TQ)

(179)

From the article "A Big New Step in the Search for ET": Describe two arguments in favor of Optical SETI searches and why other civilizations might try to use optical wavelengths instead of radio to communicate with us. (TQ)

(180)

What is the origin of the plasma (plasma just means hot, ionized gas) torus that marks out the path of Io's orbit?

(181)

Although Europa is completely covered by ice (giving it the highest albedo of any object in the solar system), we know that it is mostly rocky. Explain how we know this.

(182)

What makes the surface of Europa so young (such a low crater density, bright coloring)? Explain why we think Europa is one of the most likely objects in the solar system besides Earth to have life as we know it.