Astronomy Mod 4

Q4.1 From your textbook's chapter 8.1, how do we know that the Earth’s core is largely made up of very dense iron as opposed to the lower density types of rock that make up its crust?

There was differentiation- sorting of components by density
When the earth was still warm and molten, heavier materials sank to the middle of the earth.
seismic waves spread throughout the interior and give us density

Q4.2 From your textbook's chapter 8.2, we learned that Alfred Wegener studied the Earth’s surface extensively and came up with a theory to explain the major surface features. (a) Explain what his theory proposed, then (b) provide two examples of evidence that supported his hypothesis about the Earth.

A) He proposed the Pangea and believed South America and Africa were linked. Continental drift theory
B) Fossils in south America and Africa are similar
The resemblance of species on both continents

Q4.3 From your textbook's chapter 8.2, regarding Wegener's theory: (a) what was the major argument against his hypothesis, initially? (b) describe how this was eventually addressed by describing what causes continents to drift.

A) He was missing a mechanism. No one could explain how they separated and drifted.
B) eventually addressed by the movement of Plate tectonics

Q4.4 From your textbook's chapter 8.3, we know that the temperature of the atmosphere cools as you get further and further above the surface. But about 50 km above the surface of the Earth (in the stratosphere), the temperature starts to warm up. Explain what causes this warming in the stratosphere.

the breakup of ozone layer adds heat to the stratosphere, the ozone is a good absorber of UV light

Q4.5 From your textbook's chapter 8.3, briefly describe what we think are the two main sources of the Earth's original atmosphere (three possible sources are mentioned but only the latter two are significant).

1) it could have been released from the interior through volcanic activity
2) may have been derived from the impacts by comets and asteroids

Q4.6 From your textbook's chapter 8.4, describe two changes the occurred in the Earth's atmosphere about 2 billion years ago that allowed Oxygen to become more abundant in our atmosphere.

1) increased geologic activity led to heavy erosion, buried planet carbon before it could combine with oxygen to form carbon dioxide
2) the development of blue green algae converted carbon dioxide to oxygen

Q4.7 From your textbook's chapter 8.4, explain why the presence of Oxygen allowed for life to move out of the oceans and grow increasingly diverse.

oxygen in our atmosphere led to the formation of an ozone layer, which protected the land from dangerous uv rays and solar winds, so they could move out

Q4.8 From your textbook's chapter 9.1, describe two major differences between the composition of the Earth and the Moon.

1) moon was depleted by volatiles and silicates
2) The moon only has 1/18 the mass of earth and 1/6 of the earths surface gravity

Q4.14 From your textbook's chapter 9.5, what is the origin of the long cliffs or scarps on the surface of Mercury?

They come from the slight compression of mercury's crust, the planet shrunk after craters formed.

Q4.15 From your textbook's chapter 10.2, describe two ways that the thick atmosphere of Venus affected the appearance (or lack of appearance) of craters on the surface of Venus.

1)The atmosphere only protects Venus from small projectiles
2) larger projectiles become distorted or multiply as they break apart in the atmosphere

Q4.16 From your textbook's chapter 10.3, describe how the runaway greenhouse effect may have changed the atmosphere of Venus from its original Earth-like state to the mostly CO2, extremely hot world we see today.

An increase on CO2 and H2O gases amplify the greenhouse effect, leading to more heat and more release of the same gases, temperatures continue to rise.

Q4.17* From your textbook's chapter 10.4, a small sample of meteorites found on Earth’s surface over many years is composed mostly of volcanic basalts. Explain the two arguments Astronomers have used to deduce that the meteorites likely originated from the surface of Mars.

The theory is that the basalts come from an impact on another planet
1. the meteorites are relatively younger and have similar gases in them to the isotopes on mars.
2. It would be too difficult to eject from venus impacts to escape its thick atmosphere

Q4.18 From your textbook's chapter 10.4, why do we think the largest Martian volcano, Olympus Mons, may still be active?

It has very few impact craters and its surface is about 100 million years old or even younger
fresh looking lava flows that look geologically quite young

Q4.9 From your textbook's chapter 9.1, although the Moon has no atmosphere, water-ice does exist on the surface in some places. Explain how this is possible.

From comets and meteorites impacting the surface
small bits of atmosphere that can be retained on the moon are quickly frozen to the ground

Q4.10 From your textbook's chapter 9.2, why are the mountains of the Moon mostly smooth and rounded in shape instead of sharp and steep like many of the mountains on Earth?

The moon does not have elements of erosion like wind, ice, and rain to carve steep and sharp cliffs
Gradual erosion and meteor impacts

Q4.11 From your textbook's chapter 9.3, explain (a) why scientists first proposed (two reasons) that craters on the Moon were due to impacts rather than volcanism and (b) why almost all of the lunar impact craters are circular instead of oval.

A) 1. large lunar craters are larger and have different shapes from volcanic craters on earth
2. terrestrial volcanic craters are smaller, deeper, and occur at the tops of volcanic mountains
B) When objects hit the surface they have so much momentum that they create a symmetrical circular impact

Q4.12* From your textbook's chapter 9.3, describe the evidence in the lunar maria and highlands that indicates the cratering rate on the Moon hasn’t always been constant, but instead there was an early era of heavy bombardment, then a slower, constant rate from that point forward.

the lunar highlands has over 10x the amount of craters compared to the maria. had it been at a constant rate over time, the maria would be much older

Q4.13* From your textbook's chapter 9.5, describe how radar measurements of Mercury revealed its rotation rate to astronomers on Earth (explain or use a simple diagram to show what the observations would look like if Mercury were rotating slowly vs quickly and explain the difference).

radio signals either have a blue shift or a red shift when bouncing off of rotating planets. the faster is rotating the larger it has on the pull or shift.

Q4.19 From your textbook's chapter 10.5, runoff channels (that look like dried up river deltas) are by-products of a time when Mars had continuously flowing water on its surface. About how old are these channels, and how do we know their age?

estimate the age by looking at the crater records- more cratered than the lunar maria but less than the lunar highlands, they are probably 4 billion years old.

Q4.20 From your textbook's chapter 10.5, one of our Martian rovers (Opportunity) appears to have landed in an old lakebed that contained a salty lake at one time. What are two arguments Astronomers use to argue that the landing site was once underwater?

1) Rocks contained chemical evidence at evaporation- there must have been a lake there
2) rocks were rich in the material hematite which can only form in watery environments.

Q4.21 From your textbook's chapter 10.5, describe the positive feedback cycle (the "runaway refrigerator" effect) that the authors speculate may have led to the loss of the Martian atmosphere.

Mars has a lower gravity- atmospheric gases can escape more easily
-> the surface temp dropped, water froze out of the atmosphere, cooling the atmosphere even more

Q4.22* From the Scientific American article "Mars in Motion," the "gullies" observed frequently on Mars were originally thought to be some manifestation of flowing water (though there were problems with this hypothesis as mentioned at the opening of the article). Eventually, the HiRISE mission came up with enough observational data to convince scientists that the gullies are caused by sublimation of carbon dioxide frost. Explain two lines of evidence that led scientists to this conclusion.

1) Images showed frost covering the slope of a crater rim, but was not in some of the gully channels- something was happening within the gully
2) happen more in the south which has colder winters
3) the gullies become active when carbon dioxide frost covered the ground

Q4.23* From the Scientific American article "Mars in Motion," another type of feature observed on Mars is the "Recurring Slope Lineae" (or RSL). Describe two arguments to suggest these are associated with flowing water (one from page 62, one from page 65).

1) mars contains salty surfaces allows water to remain liquid even in freezing temperatures
2) the water is below the surface and is revealed in late summer, therefore it must be under the surface

Q4.24 From the Scientific American article "Mars in Motion," explain why the Southern Hemisphere on Mars has more extreme seasons (warmer summers, colder winters) compared to the northern hemisphere.

Mars follows an elliptical orbit gets closer to the sun at perihelion (located on the southern hemisphere)

Q4.25* From the Scientific American article "How to Search for Life on Mars," (a) describe how the first Viking experiment searched for life in the Martian soil, and (b) explain how the presence of perchlorate in the soil explains the "false positive" results from Viking.

A) They took scoops of martian soil and added carbon compounds as food for many microorganisms. If there was microbes in the soil, they would release carbon dioxide.
B) Because the viking heated soil before beginning, perchlorates would react and release oxygen and chlorine

Q4.26 From the Scientific American article "How to Search for Life on Mars," one modern approach suggested by the article for detecting life on Mars involves searching for DNA molecules. What's the argument against this approach?

DNA might not be present in alien life, or could be so different it is missed.

Q4.27 From the Scientific American article "How to Search for Life on Mars," another approach for detecting life would be to look for certain proteins in the soil. Describe two strategies suggested to select which proteins to look for out of the millions of possibilities.

1) Look for proteins that would be useful or essential to survival on mars
2) Target molecules that are ubiquitous throughout the microbial world

Q4.28* From the Scientific American article "How to Search for Life on Mars," describe two important factors that make it more probable for life to be present, which will then help us to select a landing site for this proposed mission to Mars.

Ice and Salt are friends to bio makers- protects them from damage and decay
1) Icey sites that may harbored recent life
2) Sites where erosion has recently exposed the ancient material

Q4.29 From the video "The Clean Room," how can we figure out how much lead was originally present in any given rock on the Earth, given that these rocks have changed their compositions over time while on the Earth.

if a meteorite falls to earth we can measure the lead in it which tells us how much lead existed on early earth meteorites are unchanged since their formation

Q4.30 From the video "The Clean Room," when Clair Patterson tried to measure the amount of lead in zircon crystals, he got wildly inconsistent results, unlike his colleague's measurements of uranium in the same crystals. Explain what was causing the problem with Patterson's experiment.

there is so much lead in our environment that can contaminate samples but there is not any uranium that contaminates

Q4.31 From the video "The Clean Room," (a) although lead is toxic and may have eventually led to the downfall of the Roman Empire, why was it used so much by the Romans? (b) Also, explain two ways in which lead harms humans at a microscopic level.

A) lead was cheap, malleable, and easy to work with
B) it mimics other metals and blocks nerve transmitters

Q4.32 From the video "The Clean Room," explain how Dr. Patterson discovered that lead is not naturally abundant in the environment but instead had increased dramatically in our environment within the past hundred years or so.

comes from leaded gasoline

Q4.33 From the short video "Birth of the Moon," explain how the lunar maria formed and why their appearance is so dark compared to the lunar highlands.

formed from impacts hitting the moon- because the core had not cooled down yet, so lava seeped into the craters filling them in- high iron content reflected less light and appeared darker

Q4.34 From the video "Crash Course: Tides," the strength of the tidal force depends on three things. Briefly describe each of these three things.

gravity- the stronger the gravity, the stronger the tidal force
size- wider= stronger gravity= stronger tidal force
distance- further= lower tidal force

Q4.35 From the video "Crash Course: Tides," explain why the Earth has TWO tidal bulges and not just one that is closer to the Moon.

the side not facing the moon feels a weaker force from the moon than the earth's center- the center of the earth is being pulled from the far side- causing bulges on opposite sides

Q4.36 From the video "Crash Course: Tides," what causes the Moon to move gradually further away from the Earth over a very long time?

the earth is spinning faster than the moon but still is being pulled by it- pulls the moon forward by the gravity of the bulges, then the moon tries to pull back

Q4.37* From the video "Crash Course: Tides," what causes “extra high” high tides, even higher than what you would normally see during Spring tides? These kinds of tides are called proxigean tides.

These tides occur when the moon is at its closest point in its orbit to the earth and spring tides are happening at the same time

Q4.39 From the video "Venus Could Have Supported Life for Billions of Years:" briefly describe two different theories proposed by the narrator to explain why Venus might be rotating so slowly today.

Venus was smashed by a planetoid
Tidal interactions with the sun slowed the rotation

Q4.40* From the video "Venus Could Have Supported Life for Billions of Years:" in the simulation described in the video, Venus is supposed to have started with a thick atmosphere of mostly Nitrogen and oceans of water all over the surface. What did the simulations show about the long-term evolution of Venus’ atmosphere over the first 3 billion years or so of its history

The carbon dioxide was drawn away and locked into silicate rocks
In every model they found that venus was able to maintain stable temps for almost 3 billion years due to the presence of liquid water

Q4.38 From the video "Venus Could Have Supported Life for Billions of Years:" explain how we know that Venus once likely had shallow seas all over its surface with depths ranging from a few feet to perhaps hundreds of feet.

They calculated how much deuterium and hydrogen is in its atmosphere

Q4.41 From the video "Crash Course - Mars:" what is thought to be the cause of the huge difference in geography between the northern and southern hemispheres of Mars?

a large impact that changed the southern hemisphere

Q4.42 From the video "Crash Course - Mars:" describe the evidence that tells us that frozen water probably exists in many places just beneath the surface of Mars at mid-latitudes, not just at the polar caps.

recent small asteroid impacts have a white area around them- underground deposits of ice

Q4.43* From the video "Crash Course - Mars:" why does the narrator argue that life could have potentially formed on Mars even before it formed on Earth, billions of years ago?

Life started on earth when the surface started to cool- Mars is smaller and cooled faster after its formation
a rover detected simple organic molecules on Mars- the ingredients for life are there

Q4.44 From lecture, describe how Earth's magnetic field (a) is formed, what ingredients are necessary for a planetary magnetic field and (b) protects us from the solar wind.

a) moving charges, moving-rotation, charges- internal heat
b) magnetic field blocks the motion of moving charges- blocks solar wind and diverts from earth

Q4.45 From lecture, (a) what are two effects the solar wind can have on a planet unprotected by a magnetic field, and (b) how is each effect harmful to potential life on the surface of such a planet?

A) high energy collisions can sterilize the planet
solar winds can strip atmosphere
B) molecules can pick up speed and escape the atmosphere, sputtering

Q4.46 From lecture, describe what causes the aurora (aurora borealis and aurora australis) close to each magnetic pole of the Earth.

spiral around the magnetic lines that cause them to gain a lot of energy- causing atmosphere to glow
when solar activity is more than usual, the solar wind can cause even pressure to expand the aurora lines

Q4.47 From lecture, (a) briefly explain the fission theory for the origin of the Earth's moon. How does the fission theory explain (b) the lack of metal in the Moon relative to the Earth and (c) the fact that Earth and Moon rocks have very similar isotope fingerprints?

A) Fission Theory- the earth was spinning quickly after it formed causing parts of the mantle near the equator to fly into space
B) if the moon originated from the earths mantle, this would explain the lack of metals on the moon because the mantle has less metals.
C) Because the moon is a piece of the earth, it would make sense that they have the same fingerprints

Q4.48 From lecture, briefly describe two problems with the fission theory for the Earth's moon (two reasons why astronomers today do not believe it is a valid explanation).

1) The moon does not have volatiles and fission theory does not explain why they arent around
2) we cannot explain how the earth would spin fast enough, making it unlikely for a piece to fly off

Q4.49* From lecture, briefly describe the capture theory for the origin of the Earth's moon, and explain two problems with the theory from a scientific standpoint.

A) The earth and the moon formed independently, the two had some interaction and the earth "Captured" the moon
B) 1. how do they have the same isotopic fingerprint
2. escape velocity- if the moon is moving fast enough towards the earth, then it is faster than the escape velocity and would escape into space
2. planet is too big

Q4.50* From lecture, briefly describe the giant impact theory for the origin of the Earth's moon. How does the giant impact theory explain (a) the lack of metal in the Moon relative to the Earth, (b) the fact that Earth and Moon rocks have very similar isotope fingerprints, and (c) the relative lack of volatiles in lunar rocks compared to the Earth.

A) lack of metal- chunk of the mantle was knocked off
B) it is a part of the earth
C) if it comes from our mantle, then it is hot enough to burn of the volatiles

Q4.51 From lecture, briefly describe the four major sources of gas in a planetary atmosphere.

1) outgassing- volcanism, geysers, etc
2) small impacts- dust that catches particles from space and enters our atmosphere and comets that contain methane
3) evaporation/sublimation- water vapor into the atmosphere
4) chemical reactions- photosynthesis or respiration

Q4.52 From lecture, briefly describe the four major sinks of gas in a planetary atmopshere.

Thermal escape- gases that get too hot that they move too quickly and escape
solar wind stripping- our magnetic field mostly protects us from this
condensation- for water-rainfall
chemical reactions- photosynthesis and or respiration.

Q4.53 From lecture, briefly explain why the Copernican Principle would lead us to believe the Earth and Venus likely had similar atmospheres originally.

copernican principle is nothing about the earth is special
both atmospheres were probably formed by outgassing and impacts- before that they were similar

Q4.54 From lecture, for each of the possible sinks of atmospheric gases (thermal escape, solar wind stripping, condensation and chemical reactions), explain why Argon does not leave an atmosphere but instead remains at a constant abundance over time for worlds like Earth and Venus.

argon is one of the heaviest gases and moves slowly.
argon sits on the surface/bottom of venus
you cant condense argon unless planet is super cold
argon is a noble gas and is not effected by chemical reactions

Q4.55* From lecture, explain how we use Argon to argue the Earth and Venus originally had similar atmospheres. Describe the logical sequence that starts with Argon measurements and ends with the conclusion that the two worlds had similar atmospheres originally.

1) Despite overall differences in our atmospheres today, the amount of argon present today is the same
2) because argon does not change over time, they must have had similar abundances of argon originally

Q4.56 From lecture, explain two important differences between Venus and Earth that led Venus to lose much of its water vapor while Earth is not really vulnerable to this sort of effect.

1) venus lacks a magnetic field- vulnerable to solar winds
2) venus lacks an ozone layer due to the lack of O2, which would block uv light

Q4.57 From lecture, explain why heavy water is enriched on Venus compared to the Earth.

because water is heavy it sits at the bottom of venus' atmosphere. Venus is more vulnerable to solar wind and thermal escape, the lighter water escaped more easily leaving heavy water behind

Q4.58* From lecture, describe the evidence (3 parts) from the Magellan explorer that led scientists to the conclusion that Venus resurfaced itself somehow about 500 million years ago.

1) venus has about 5x more craters than earth- it must have solidified 500 million years ago
2) craters are distributed uniformly on venus- entire surface solidified at the same time
3) craters are pristine- no gradual way to erase craters, must be quick and catastrophic

Q4.59 From lecture, aside from the "runaway refrigerator" process from Q4.21, describe two additional ways that the Martian atmosphere may have been lost over time (and why each of these doesn't happen to Earth).

1) thermal escape because Mars has such a low gravity that gases can escape easier, this does not happen on earth because we have more gravity
2) Solar wind stripping could strip lots of gases from the atmosphere. This doesn't happen on earth because we have a gravitational field.

Q4.60 From lecture, explain (a) why Argon reconstruction cannot work on Mars and (b) the evidence that some Argon has managed to escape from Mars.

a) argon can escape from Mars if it attaches to solar winds- cant serve as a tracer
B) Isotopes of 38Ar have depleted on mars bc it escaped