AST248-Midterm2
The reason that Venus is so much hotter than the Earth is
its thick, carbon dioxide atmosphere creates a far stronger greenhouse effect
moons
moons are a lot like planets in composition but they do not orbit the sun directly, they orbit planets. The composition of moons varies with distance from the sun in essentially the same way as planets, moons closer to the sun are made of rock and metal while moons further away are composed mainly of ice (the same stuff the jovian planets are made of, but frozen).
Stars generate luminosity from
nuclear fusion
In the core of the Sun
nuclear fusion causes protons to combine to form helium nuclei.
People belong to the domain
Eukarya
The most abundant element in the universe is
Hydrogen
If you observe an absorption line spectrum, what can you say about the temperature of the foreground gas relative to that of the background continuum source?
It is cooler than the continuum source.
According to observations, the overall chemical composition of our solar system and other similar star systems is approximately...
98% Hydrogen and Helium, 2% other elements
Define what we mean by the term "Habitable Zone".
That region where water can exist as a liquid.
What evidence suggests that water might still flow at or beneath the martian surface today? Why do we think that Mars might still have subsurface liquid water today?
The first evidence suggesting that water might still flow is the existence of gullies on the crater walls. Signs of recent flowing water may suggest water springing up from underground before it evaporates.
an O star on the main sequence
Unlikely: the star is too young. also Unlikely: this phase of stellar evolution is too short.
What is this term? (write a phrase explaining what N* means; do not write down a number)
The number of stars in the Galaxy.
If you observe a hot background object which emits a continuous spectrum through a cool gas cloud, you will see
an absorption line spectrum.
Identify the FALSE statement. Sunspots
are hotter than the photosphere.
Mars is not tectonically active today because
it cooled off rapidly because it is smaller than Earth.
Venus is much hotter than Earth because
it has a very strong greenhouse effect.
The age of our solar system is about...
one-third the age of the universe.
Transits
small planets orbiting close to M stars
terrestrial planets
smaller and less massive (but more dense) of the two types of planets. They are located closer to the sun and are composed primarily of rock and metal. They have fewer moons than jovian planets and no rings. They also have a solid surface.
The total number of stars in the visible universe is about
the same as the grains of dry sand on all the beaches of Earth.
Outline the main differences between Bacteria and Eucarya.
Bacteria have no nucleus or other intra-cellular bodies. They have a single strand of DNA. Eucarya are larger. They may have multiple strands of DNA, protected within a nuclear membrane. They contain other small objects, sich as mitochondria or chloroplasts, and ribosomes.
Why do the Moon and Mercury seem unlikely to be habitable? Does evidence for ice in lunar craters affect the answer?
Both the Moon and Mercury seem unlikely to be habitable due to the lack of water. There is little water on both the Moon and Mercury. In particular, the book mentions that during the day Mercury is far too hot for liquid water and at night it is far too cold for liquid water. As for the Moon, there is water ice hidden at the bottom of polar craters which has been confirmed. However these craters would not help since the ice never melts.
Is a light year a measure of distance or a measure of time?
Distance. It is the distance that light travels in one year, or about 1018cm.
Briefly summarize the evidence, both real and imagined, that led to widespread belief in a martian civilization by the end of the nineteenth century.
During the nineteenth century, it was noted that Mars was similar to the Earth. A day on Mars was about 24 hours and had polar ice caps. It was also speculated that some thought they saw surface canals on Mars.
Earth has far less atmospheric carbon dioxide than Venus because
Earth's carbon dioxide is locked up in carbonate rocks
The most common rock type in the strata of the Grand Canyon is sedimentary rock.
This makes sense. The answer is given to you on page 106 on the textbook.
What do we mean by the geological record? Why is it important?
The geological record is the information about the Earth's history through the study of rocks and fossils. It is important because with this information, we can understand how the Earth has developed over time.
The half-life of carbon-14 is
The half-life of carbon-14 is about 5700 years.
Summarize the evidence suggesting that Mars must have been warm and wet, possibly rainfall, in its distant past.
There are orbital images that suggest the existence of terrain features which may be due to flowing water, such as dried up riverbeds and erosion. Rovers have found mineral traces that normally form in water.
Why isn't liquid water stable at the martian surface today? What happens to water ice that melts on Mars?
There is no liquid water on the surface of Mars due to a few reasons. Mars is very cold most of the time (thin atmosphere). As a result most of the liquid water on the surface would freeze into ice. Even as the temperature increases, Mars still has very low atmospheric pressure which would cause the water to evaporate.
A Separate Origin? Suppose that we someday discover life on Mars. How might we be able to determine whether it shares a common origin with life on Earth (perhaps suggesting that life traveled on meteors between the two planets) or has a complete separate origin? Explain clearly.
We begin by analyzing the question. If Martian life and Earth life shared a common origin, we would look for properties that share a common trait by coincidence. One example to determine if life on earth has a common ancestor is looking at the chirality of amino acids. Chirality simply means mirror image. Living cells on Earth have adapted to using left-handed amino acids to create proteins. If life on Mars also shares this same abundance of using left-handed amino acids, this would be a good way to check if there was a common origin between life on the two planets. Another example would be looking at the structural unit of energy, ATP. All life on Earth use ATP for energy storage. If life on Mars uses this same molecule for energy storage, it would offer more evidence for a common origin of life.
The first evidence for life on Earth is
a high 12C/13C ratio at 3.8 Gya.
Identify the FALSE statment. The Greenhouse Effect
causes the Earth's albedo to decrease.
Compared to liquid water, liquid methane is
colder
Doppler Wobble
hot Jupiters.
Frozen lakes often have liquid water beneath their icy surfaces primarily because
ice floats and provides insulation to the water below
Kuiper belt objects
large Kuiper belt objects are very similar to comets in that they are made of the same stuff and orbit the sun from far off in the Kuiper belt. How- ever, since they are much larger than the average comet astronomers are reluctant to refer to them as comets, hence the term Kuiper belt object.
Direct Imaging
large planets far from their stars.
jovian planets
larger, more massive, and less dense than terrestrial plan- ets. They are composed primarily of hydrogen, helium, and hydrogen compounds like water and methane. They have many moons as well as rings of smaller satellites. They do not have a solid surface.
The value of NH in Drake's equation is
probably close to 1.
Earth has retained a lot of internal heat primarily because of its
relatively large size
The wavelength at which a blackbody is brightest tells us its
temperature (Wein's law)
The apparent brightness of an object is proportional to the distance to the object to what power
-2 (the inverse-square law)
On an asteroid that is twice as far as the Earth from the Sun, the strength of sunlight would be
1⁄4 as great as on Earth
Did you read the course web page? How many midterms will there be?
2
The distance to the Moon is about two hundred forty thousand miles. Write this number using scientific notation.
2.4 X 105 km
You have a rock that today contains 3 atoms of 40Ar for every atom of 40K. When the rock solidified, it contained no 40Ar. The half-life of 40K is 1.25 Gyr. The age of the rock is
2.5 Gyr. Originally you had 4 atom of K and none of Ar. After 1 half-life two of the K become Ar, so it is 2:2. After the second half-life half of the remaining 2 K atoms (that is, 1) decaus, so you now have 3 Ar atoms for every K atom.
The average distance between stars in our part of the Galaxy is about how many light years
4
The numerical value of N* is about 400 billion (400 thousand million if you are British). In scientific notation, this number is written
4 x 10^11
What would the numerical value of N* be in a dwarf galaxy with 10-4 the mass of the Milky Way Galaxy?
About 4 x 107 The mean mass of a star is the same.
Why do the Moon and Mercury seem unlikely to be habitable? Does evidence for ice in lunar craters affect the answer? Explain.
Both the Moon and Mercury seem unlikely to be habitable due to the lack of water. There is little water on both the Moon and Mercury. In particular, the book mentions that during the day Mercury is far too hot for liquid water and at night it is far too cold for liquid water. As for the Moon, there is water ice hidden at the bottom of polar craters which has been confirmed. However these craters would not help since the ice never melts.
Why is carbon the basis of biochemistry
Carbon is one of the most abundant elements. Carbon has a valence of 4, so it can form single, double, and triple bonds. CO2 is far less stable than SiO2, enabling chemical reactions. It can bond with itself, forming long chains, which enables the complexity of biochemical molecules.
True or False: Because of their higher frequency, X-rays travel through space faster than radio waves.
False. All light travels at the speed of light.
The drilled sample showed no signs of life on asteroid B612, but we found many complex organic molecules.
I would believe this. As we have continuously learned, there is organic matter on meteors and asteroids even in the absence of life. Therefore we should not be surprised.
What are ice ages, and what may cause them? What do we mean by snowball Earth periods, and how does Earth recover from them?
Ice ages occur when the global average temperature drops a few degrees causing an increase in snowfall. They possibly have been caused by small changes in the Earth's rotation and orbit. The Earth's tilt varies with time and can affect the seasons making them less or more extreme. Snowball Earth periods are long and cold ice ages where the Earth's water freeze causing the surface to be covered in ice. The Earth recovers from these periods through the CO2 cycle. During these periods, the Earth's interior remains hot leading to volcano buildups which add to the atmospheric carbon dioxide. The building of carbon dioxide strengthens the greenhouse effect which melts the snowball Earth.
Is the value of N* very certain or very uncertain? Explain.
It is fairly well known. We can measure the density of stars, and estimate the volume of the Galaxy. The product is the number of stars.
Rock Life? How do we know that a rock is not alive? In terms of the properties discussed in this chapter, clearly describe why a rock does not meet the criteria for being alive.
Keeping the above conditions in mind, we clearly see that a rock is not alive. The only property that a rock has in common with living organisms is order. However, a rock cannot reproduce and it doesn't utilize energy. These are a few of the criteria that distinguish rocks from living organisms.
How do martian seasons differ from Earth seasons? Describe the major seasonal changes that occur on Mars?
Let us first note that both Mars and Earth have seasons due to their tilt away from their axis (Mars has a lower tilt than the Earth). There are two main reasons why the martian seasons are different for Earth seasons. 1) The Martian year is twice as long as the Earth's so their seasons are (nearly) twice as long. 2) Martian seasons are affected by their elliptical orbits. This differs from Earth as the Earth's tilt (tilt refers to angle different between the Earth and its rotation axis) is the only reason for seasons. Mars is closer to the Sun during its southern hemisphere summer and farther during its southern hemisphere winter. Planets move quicker when they are closer to the Sun (as we expect from energy conservation, the book says Kepler's second law but it's easier to understand from the former), Mars has more extreme seasons. It has a shorter and warmer summer while it has a longer and colder winter than its northern hemisphere.
How do we know that ALH84001 really came from Mars, and how have we learned its history?
Let's first note that the ALH84001 was a meteorite that was scooped up from Antarctica (Allan Hills region) in 1984. We know that it came from Mars because the gas trapped inside of it appeared to be very similar in both its chemical and isotopic composition to the atmosphere of Mars. We've learned about its history through radiometric dating and its studying its structure and composition.
an M0 main sequence star
Likely: the star may be very old.
a G2 dwarf star
Likely: this star is like the Sun
Growth and Development:
Living organisms grow and develop with a direct correlation to their ancestral history or heredity. Of course other factors may influence how organisms develop such as their environment.
Response to the Environment:
Living organisms interact with their environmental surroundings and respond to any changes. For example, the weather influences how we may dress. The book gives the example of simple organisms moving to region where the temperature is suitable for growth.
Reproduction
Living organisms reproduce either asexually like bacteria or sexually like humans and plants. This leads to the growth of a species.
Energy Utilization:
Living organisms use energy to create and maintain cell production, growth and the ability to reproduce. For example, in humans we create energy by breaking down glucose in a process known as cellular respiration. As some may know from biology, this occurs in the mitochondria. The processes involved in cellular respiration are glycolysis, the Citric Acid cycle and the electron transport chain (I said this to enrich your learning experience).
Why does Mars seem such a good candidate for life?
Mars seems like a good candidate for life because of the possibility of underground liquid water. Even though the surface water is frozen (due to the climate change), it has enough internal heat to have liquid water underground.
Describe how plate tectonics shapes important geological features of Earth, including mid- ocean ridges, continents, mountain ranges, rift valleys, and earthquakes. How did Hawaii form?
Mid-ocean ridges occur when tectonic plates move apart. The region between the plates, molten rock seeps into the ocean and eventually hardens thus causing mid-ocean ridges. Continents are formed from thick slabs of continental crust. Mountain ridges are formed when two continental plates collide causing them to be pushed upward. Rift valleys are thin patches of crust that result from continental plates moving apart. Earthquakes occur when plates scrape against each other. Hawaii was formed by plate tectonics moving the pacific plate over a hot spot. The lava erupted from the hot spot gave rise to the islands.
If you had a time machine that dropped you off on Earth during the Hadean eon, you'd be quickly killed by a large impact.
Not necessarily since the large impacts didn't occur continuously. If you happen to be transported when an impact did occur then the situation would be different.
Evolutionary Adaptation:
Over time, organisms evolve to be more adapted to their environment.
Describe the technique of radiometric dating, and explain how we know it is reliable. Be sure to explain what we mean by a radioactive isotope, parent and daughter isotopes, and a half-life.
Radiometric dating allows us to measure the age of a rock or a fossil by measuring the object's proportions of atoms and isotopes. Considering an object with both atoms of type A and B, my measuring the ratio of these atoms we can find the age. A radioactive isotope's nucleus undergoes spontaneous radioactive decay such as a proton turns into a neutron (This is known as beta plus decay, where the proton decays into a neutron, positron and an electron neutrino. The positron is the antiparticle of an electron and has positive like the proton). During the decay, A is the parent isotope and B is the daughter isotope, i.e., the decay products. The number of atoms of isotope A reduces in half in a certain amount of time known as the half-life. The following formula for the age of the object is given here: T = τ ln ((A +B)/A)/ln (2), Where τ is the half-life and ln (2) comes from the definition. The value of ln (2) is 0.693, a number worth noting. Radiometric dating is understood as we understand today the underlying physics of nuclear processes. For our purposes we don't need to know these mechanisms; to understand them, one needs quantum mechanics and some basic quantum field theory. To derive this we use the equation Division gives Taking the natural log i.e., ln = loge we get A = (A+B) 2-t/τ. A/ (A+B) = 2-t/τ. -t/τ ln (2) = ln (A/ (A+B)), Where we used the fact that ln (xy) = yln(x). Multiplying -τ on both sides gives the required result. One should note that -ln(x/y) = ln(y/x).
Which of the following is not a general difference between ter- restrial planets and jovian planets?
Terrestrial planets have oceans of liquid water and jovian planets do not.
Briefly summarize the Viking experiments and their results. Do the results constitute evidence of life? Explain.
The Viking experiments took martian soil and analyzed it to see if it contained any microbes. They exposed the soil to different conditions and looked for a biological response. Initially some of their experiments seemed to support that there was life, however the possibilities for life were eventually ruled out. Scientists deduced that this may have been caused by some chemical reactions instead of biological ones.
What were the heavy bombardment and the late heavy bombardment, and what effect might they have had on life?
The heavy bombardment period occurred in the first few hundred million years of the solar system. During this period, asteroids and comets crashed into the Sun and planets which left impact craters on the surfaces of planets and moons. The late heavy bombardment period occurred about 4.1 billion years ago and ended 0.3 billion years later. Asteroids and comets as well as other bodies crashed into the Sun and planets. These periods could have caused the orbits of the planets to change. The impacts could have affected life detrimentally. The impacts would have vaporized the oceans and raised the temperature causing the crust to melt. However, the book mentions that microscopic life living underground could have survived. It even mentions that these impacts could have increased the habitability of the Earth.
Order
The internal structure of all living organisms is ordered i.e., not randomly oriented. The book notes that order doesn't make something alive. The example they give is a book.
What is the leading hypothesis concerning how Mars lost its once-thick atmosphere? What role does Mars's size play in this hypothesis?
The lading hypothesis supporting how Mars lost its thick atmosphere has to do with its magnetic field. The book mentions that early on, Mars most likely had molten, convecting metals in its core. Both convection and rotation should have produced a magnetic field which would have protected the atmosphere. However, the magnetic field would weaken as Mars cooled down and convection stopped. As we know cooling down is due to the lack of greenhouse gases. Mars's size played a role because it was too small to retain its internal heat. As a result, over time mars would have eventually lost most of its atmosphere. Volcanic activity would have ceased as the interior cooled down and the magnetic field strength would lessen allowing solar winds to strip the gases from the martian atmosphere.
On Earth, we cannot find fossil evidence of life dating to times prior to about 3.8 billion years ago. If life ever existed on Mars, is it possible that we would find older fossils than we find on Earth? Explain.
The most important thing to consider here is the fact that geological activity on Mars has slowed down significant over time. It is possible that Mars did have significant geological activity about 3.8 billion years ago. If there are fossils older than this, then it is possible that they may be some today if they survived this activity. If this is indeed the case, we can conclude that there may be some fossils since geological activity has slowed down on Mars.
What is the potential significance of atmospheric methane to the search for life on Mars?
The significance and the intrigue arise because of the origin of the methane gas. Scientists believed that there are three reasons why methane may be present in the martian atmosphere. They eliminated the possibility of comet impacts since these are such rare events. However, the other two possibilities are still very much possible. These are both volcanism and life of Mars. Scientists believe that the presence of methane has some biological origin since they have observed that methane vary regionally across Mars and seasonally. They aren't able to completely rule out volcanic activity. Volcanism is still important since the heat necessary for methane release may be enough to have underground liquid water.
How does the strength of sunlight vary with distance from the Sun? Discuss the implications for photosynthetic life.
The strength of sunlight varies as the inverse square of the distance from the Sun i.e. d-2 as we know from the first exam. As a result, photosynthetic life would have to be much larger than life on Earth, much more efficient in collecting sunlight, and/or slower metabolic and reproduction rate. (Plant biology is the reason why I STOPPED studying biology)
Outline the main differences between Archaea and Bacteria
They resemble each other. Archaea are more primitive, and are found in more extreme environments.
Science can never be determined with confidence the times or sequence of events that occurred millions or billions of years ago.
This does not make sense. Science for example has made huge progress in understanding the beginning stages of our universe (e.g., cosmology).
A noted physicist today announced that he has found evidence that gravity operates only on Earth and nowhere else in the universe.
This does not seem reasonable either. Aside from the fact that he would have to explain why matter on Earth is unique in the sense that it is the only matter in the universe to exhibit gravitation (or at least gravitation as we know it), he would also have to explain why countless observations of distant matter agree with predictions of the theory of gravity (either Newtonian or relativistic depending on the situation).
If there were no plate tectonics on earth, our planet would be far too hot to have liquid oceans.
This doesn't make sense since plate tectonics do not cool the Earth.
Photos from future orbiters show that new gullies have formed alongside some of the ones already seen in crater walls from orbiting spacecraft.
This is believable
We discover that the martian polar caps have in the past extended more than twice as far forward the equator as they do now.
This is believable
A sample return mission finds fossil evidence not only of martian microbes, but also of photosynthetic plants that lived on the exposed surfaces of martian rocks.
This is believable if Mars was warm enough and there was an abundance of liquid water.
We find rocks on Mars showing clearly that planet once had a global magnetic field nearly as strong as Earth's magnetic field.
This is believable since there was high volcanic activity in early Mars which would be sufficient in creating a strong magnetic field.
We find underground pools of water on the slopes of one of the Tharsis volcanoes.
This is believable. Mars has retained some internal heat which makes it possible for liquid water to be underground. This heat may be volcanic heat.
The first fossils discovered on Mars come from the canyon walls of the Valles Marineris.
This is believable. The book mentions that the Valles Marineris may have been formed due to tectonic activity. It also mentions that the valley network may have been shaped by flowing water and evidence (spectroscopy) has shown minerals that may have formed in water.
We deposited bacteria that get energy from chemical reactions with sulfur compounds into the upper clouds of Venus, and they are surviving.
This is believable. The book mentions that the on the upper clouds of Venus the greenhouse effect is far weaker compared to the surface. Due to the sulfur content, chemical reactions may provide enough energy for extremophiles to live in the upper clouds.
I was part of the first group of people to land on Venus, where we found huge, ancient cities that had been hidden from view by cloud cover.
This is highly not believable. Even though one may argue that the Sun was dimmer in the past, we have to remember that the high level of carbon dioxide in the atmosphere of Venus causes it to be very hot. This would not allow for the presence of oceans and it is too hot for ancient cities to be there.
We find a lake of liquid water filling a small crater close to one of the dry river channels.
This is not believable since surface flowing water would either be evaporated or frozen.
Astronomers have discovered another star system that is virtually the reverse of ours: It has all its gaseous planets, icy moons, and comets in its inner regions, and its rocky planets and asteroids in its outer regions.
This is not reasonable unless the solar system were formed in a different manner than ours. The parts of the nebular model that predict gas giants in the outer region and terrestrial planets in the inner region should not be specific to our solar system. Hydrogen should condense at the same temperatures everywhere in the universe.
We discover a string of active volcanoes in the heavily crated southern highlands.
This is somewhat surprising. We know that volcanic activity has decreased over time. Otherwise, Mars have a thicker atmosphere than it does today.
We discover Mars was subjected to global, heavy rainfall less than 1 billion years ago.
This is surprising. The book states that there was stable rainfall during some periods between 2 and 3 billion years ago.
The first human explorers on Mars discover that the surface is littered with the ruins of an ancient civilization, including remnants of tall buildings and temples.
This is surprising. There would have been evidence supporting this as there have been extensive observations made on the Mars's surfaces.
What is this term? (write a phrase explaining what fs means; do not write down a number)
This is the fraction of stars that are suitable for supporting a habitable planet. We might want to exclude the massive, short-lived stars because it is unlikely that intelligent life will have long enough to develop. We might want to exclude giant and supergiant stars, white dwarfs, and certain types of binary stars. Technically, the star itself doesn't support life - you need a planet.
We can expect that if there are paleontologists a few million years from now, they will find fossil remains of almost every human who ever lived.
This is unreasonable considering most organisms do not fossilize.
Although the Earth contains its densest material in its core, it's quite likely that terrestrial planets in other star systems would contain their lowest density rock in their cores and the highest density rock in their crusts.
This is unreasonable. We should expect to see the same due to gravity.
We can learn a lot about the Earth's early history by studying the Moon.
This makes sense since the Earth and the Moon are relatively close to one another. Due to this proximity, they would have experienced the same effects.
If nitrogen were a greenhouse gas, our planet would be far hotter than it is.
This makes sense. Due to the large abundance of nitrogen, if it were a greenhouse gas the temperature would increase. Greenhouse gases increase the temperature of the Earth.
Nearly all the rocks I found in the lava fields of Hawaii are igneous.
This makes sense. Igneous rocks are made from molten rock.
Without the greenhouse effect, there probably would be no life on Earth.
This makes sense. Without the greenhouse effect, the Earth would be too cold for liquid water as evident in the discussion of ice ages (see discussion above).
Saturn is presently at a distance of about 10 AU from the Earth. How long does it take a radio signal from the Cassini spacecraft to reach the mission control center in California? Radio waves travel at the speed of light, which is 3 x 105 km/s. 1 AU is 1.5 x 108 km.
Time = Distance/Velocity = 10 AU x 1.5 X 108km/AU / 3 X 105 km/s = 5000 seconds = 83 minutes
State the "Faint Young Sun Problem", and suggest a possible solution
Today the equilibrium temperature of the Earth is below the freezing point of water. 4.5 billion years ago the Sun was 30% fainter than today, so the Earth would have been commensurably cooler. With its current atmosphere, the Earth would have frozen solid, and there has not been enough energy received from the Sun to melt the Earth since then. The paradox is that despite the expected low temperatures, the surface temperature of Earth has always permitted liquid water on its surface. The solution is that the Earth's atmosphere has changes. There was a much stronger greenhouse early on.
a G2 supergiant
Unlikely: the star recently expanded and swallowed or fried its inner planets. also Unlikely: this phase of stellar evolution is too short.
Why do we conclude that Mars must once have been warmer with a thicker atmosphere, and what gases could have made such an atmosphere possible?
We conclude that Mars must have once been warmer with a thicker atmosphere due to the volcanic activity. Volcanic activity would have released carbon dioxide thus making a denser atmosphere.
Why do we expect the elements of life to be widely available on other worlds? How does the requirement of organic building blocks further constrain the prospects of habitability?
We expect the elements of life to be widely available on other worlds since they are abundant in the universe. Planets were built when particles condensed from gas, which eventually formed into planets. As mentioned in the book, we would expect to see heavier elements than hydrogen and helium due to the condensation process. These elements, of course include carbon. The requirement of organic building blocks further constrain prospects since these molecules need aqueous solution, in particular water.
How do we know that different regions of the martian surface date to different eras in the past? What have we learned about changes in martian volcanism during the past eras?
We know that different regions of the martian surface date to different eras in the past because the crater densities are different. Regions with more craters mean that there was less geological activity to change the surface and remove the craters. From this analysis, we know that volcanic activity on Mars has died down over the past few billion years.
Temperatures on Mercury are
very hot in the day and very cold at night
Why do we say that living cells are carbon-based? Briefly discuss whether life elsewhere could be based on something besides carbon.
We say living cells are carbon-based because carbon atoms are essential in creating more complicated molecules such as proteins etc. What makes carbon atoms so special are their bonding properties (quiz 4). Carbon can form stable single, double, and triple bonds with other molecules as well as form long chains and bend itself. It would be difficult for life to form from something other than carbon. Carbon is in group 14 of the periodic table so we may expect other elements of this group to have similar properties like silicon. However, as you progress down the group, the atoms become bigger and have different bonding properties than carbon. Silicon weakly bonds with other atoms making them less stable.
Are there habitable zones around all stars?
Yes. All stars are hotter than the boiling point of water. The equilibrium temperature at a given distance depends on the luminosity of the star, the distance from the star, and the albedo of the planet, and drops to zero as you move away from the star. Planetary atmospheres modify the surface temperatures, but I did not ask about that.
asteroids
asteroids are composed of metal and rock like terrestrial planets, but they are much smaller. Unlike moons however, asteroids do orbit the sun directly instead of a planet.
comets
comets are like asteroids in that they are relatively small objects that orbit the sun. However, their composition is closer to that of the jovian planets and their moons - they are made of ice. Note that, as we would expect, asteroids orbit close to the sun while comets tend to be farther away in the Kuiper belt and Oort cloud.
On Venus, liquid water
does not exist anywhere. The clouds are H2SO4, not H2O
Oxygen and Carbon are
the 3rd and 4th most abundant elements in the universe.
Which of the following is not a key property of life?
the ability to violate the second law of thermodynamics In case you forgot, the second law of thermodynamics says that the entropy of any closed system should increase with time. It also says that heat moves from an area of hotter temperature to colder temperature. Another formulation is that heat cannot move from a colder temperature to a hotter temperature. Interestingly we know of an everyday piece of equipment that does this, a refrigerator. However it doesn't violate this law because it does work, you need to do work to move heat from a colder temperature to a warmer temperature. That is why the back of your refrigerator is so hot; it's doing work.
Which of the following is not considered a key piece of evidence supporting a common ancestor for all life on Earth?
the fact that all life on Earth is carbon-based.
Generally speaking an extremophile is an organism that
thrives in conditions that would be lethal to humans and other animals
