ASTRO TEST 3
Although both Venus and Mars have atmospheres made almost entirely of Carbon Dioxide, Mars doesn't have a major "greenhouse effect"; why not?
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Which properties of Mars make it the most likely place to find evidence for past (or even current) life? Has any direct evidence been found?
"Splosh Craters", Gullies, Runoff Channels (rivers) (only in highlands) The energy received by the Martian surface over the year is in direct proportion to the orbital eccentricity. The eccentricity is not fixed but, is under the gravitational influence of the other planets (especially Jupiter). The eccentricity cycles and at times the orbit is more circular. As the planet changes from an elliptic orbit to a quasi-circular one, the energy balance strongly differs from one epoch to another. We are trying to understand the changes -- we anticipate that there would be "warm periods" where increased sublimation of polar CO2 ice would lead to the release of more gas into the atmosphere, thus to a greater atmospheric pressure. As the inclination of the planetary spin axis is also subject to significant cyclic variation, we suspect that the distribution of surface heating by the Sun should have experienced cyclic change over the millenia. This cycling of the martian orbit and of its spin axis make Mars an unusually variable planet (all the planets experience cycling of their "orbital elements" but some more than others). Thus Mars may well once have been quite different from the way we see the planet today.
Earths Mantle
- different composition: ROCK (not metal) - heated from below and by radioactive decay within - lower mantle: hot, but very high pressure; rocks can not move - upper mantle: not as hot, but lower pressure; rocks behave like "plastic"; rock can convect like a liquid (even though it is still solid) - asthenosphere: soft upper part of mantle - lithosphere: solid plates of the "crust" and top of mantle
How can we "probe" the interior of the earth?
1. compare their mean density and "uncompressed" density 2.The magnetic field 3. Measuring P & S waves together by using a global network of seismographs
Why are planetary interiors hot?
1. gravitational contraction (mostly for Jovian's) 2. primordial heat (accretion) 3. Radioactive decay of heavy elements
What are the sources and sinks of atmospheric gas?What interactions between the Earth's various systems keeps the sources in balance with the sinks?
A source is any process or activity through which a greenhouse gas is released into the atmosphere. Both natural processes and human activities release greenhouse gases. A sink is a reservoir that takes up a chemical element or compound from another part of its natural cycle. sinks such as the soil, the oceans and other waters, or vegetation and other biological systems, reducing the excess to background concentrations. Natural sources of carbon dioxide are more than 20 times greater than sources due to human activity, but over periods longer than a few years natural sources are closely balanced by natural sinks, mainly photosynthesis of carbon compounds by plants and marine plankton. As a result of this balance, the atmospheric mole fraction of carbon dioxide remained between 260 and 280 parts per million for the 10,000 years between the end of the last glacial maximum and the start of the industrial era.
How do we know that impacts were far more frequent 3.5 to 4 billion years ago than they are now? What is our best current theory for how the Moon was formed; when did that happen?
According to the "giant impact" theory, the young Earth had no moon. At some point in Earth's early history, a rogue planet, larger than Mars, struck the Earth in a great, glancing blow. Instantly, most of the rogue body and a sizable chunk of Earth were vaporized. The cloud rose to above 13,700 miles (22,000 kilometers) altitude, where it condensed into innumerable solid particles that orbited the Earth as they aggregated into ever larger moonlets, which eventually combined to form the moon. By measuring the ages of lunar rocks, we know that the moon is about 4.6 billion years old, or about the same age as Earth.
What causes mountains to form on the Moon?
Another cause of lunar mountains was volcanic activity- even after the surface of the moon was cool, the interior remained hot, and contained volcanic magma under intense pressure. Every so often, the pressure caused this magma to burst through to the surface as volcano's- the lava and ash that spewed forth fell back as a hard deposit around the mouth of the volcano's, which over time built up to form mountains. A third cause of lunar mountains, which happened to a far greater extent upon the Moon than on Earth, was meteor strikes. Over billions of years, the Moon has been bombarded with many thousands of huge meteors- their impact was so massive that they left the craters on the face that we see today. Debris thrown up from the impacts was pushed outwards and upwards, to form ridges of mountains.
Why is the surface so "young"? How does volcanic activity on Venus differ from that on the Earth and Mars?
As a result of the accretionary heating and heat produced by the decay of radioactive elements, the interior of the planet differentiated into layers of different composition and density, probably forming a metallic core, and a mantle and crust of silicate minerals. The period of differentiation must have occurred during a period of intense meteoritic bombardment but no tracts of heavily cratered terrain have been preserved. All of the surface of Venus is younger than the period of accretion and differentiation. This volcanic rise, and other similar uplands and their rifts, may be the result of tectonic doming and stretching of the lithosphere above upwelling mantle plumes. In many ways, they resemble the lithospheric domes on Mars, Tharsis and Elysium, with their fault-bounded rifts and associated volcanoes, but the venusian features also have some similarity to the rift valleys on Earth, such as the East African rift.
How does the crater density on the surface tell us that the entire surface is only a few hundred million years old?
Because our knowledge of age relationships is very limited, comparisons with the other planets are useful in formulating a speculative geologic history of Venus. Essential to understanding planetary history is the development of a geologic time scale based on a knowledge of the sequence of events that produced the various features and rock bodies exposed at the surface. On Earth, Mars, Mercury, and the Moon, the principle of superposition has been used to create a stratigraphic or relative time scale. In some cases, radiometric dates and crater frequencies have allowed a more quantitative assessment of the timing of geologic events. Because of the low crater density and lack of radiometric ages, such evaluations are presently difficult. We can paint the geologic history of Venus only with broad, crude brush strokes, by integrating what we know about its surface and employing analogies with the rest of the inner planets, particularly the Moon and Earth.
How do the northern and southern hemispheres of Mars differ from each other?
Cratered Highlands of the Southern Hemisphere: The southern hemisphere has many large, multi-ring craters and basins, and volcanic intercrater terrain, very similar to Mercury and the Earth's Moon. The Plains of the Northern Hemisphere: Volcanic plains, huge crustal uplifts, and volcanic shields dominate the Northern Hemisphere of Mars. Elysium and Tharsis regions represent major sites of volcanism on Mars. This is strikingly different from the southern Cratered Uplands, and the lack of dominating craters in the north probably indicates that it is much younger. The equatorial regions harbors the Valles Marineris - a gigantic rift zone - and the Tharsis Bulge. Giant shield volcanoes lurk in the Tharsis region. The largest mountain in the solar system is Olympus Mons; 700 km at its base, 2km wide at the peak, and 27 km tall! How did it get so big? We discussed why mountains can grow bigger when gravity is less (the mountains don't weigh so much, so they don't sink into the crust so far), and we pondered how Hawaii might look in the absence of continental drift. I showed images of giant impact basins (there are fewer than on the Moon, indicating that it has a younger surface), crater counts in the two hemispheres. Next time we will explore the evidence for water on the surface of Mars.
Why does the Moon have far more impact craters than the Earth, even though we are a bigger target?
Craters are destroyed by erosion (wind, rain, etc.) on Earth, but not on the Moon
What is the "evidence" that liquid water once flowed on the surface of Mars?
Dendritic river channels, dry river valleys, and outflow channels can be seen on Mars, which leads us to believe that surface water did once exist on Mars, but has since been locked up as ground ice and in the polar ice caps. There is also evidence of catastrophic flooding occurring on Mars many years ago. Teardrop-shaped islands and chaotic terrain attest to the outflow of huge amounts of water over the Martian landscape.
What are the differences between oceanic and continental crust (study this in detail)?
Earth's Crust: There are two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents. These two different types of crust are made up of different types of rock. The thin oceanic crust is composed of primarily of basalt and the thicker continental crust is composed primarily of granite. The low density of the thick continental crust allows it to "float" in high relief on the much higher density mantle below. Both types "float" on the denser, plastic-like mantle. Continents pile up higher, heavier, and less dense. Oceanic crust is younger than continental crust (200 million years old or less) due to continuous recycling at subduction zones. CONTINENTAL CRUST 45% of surface and Thicker: 20 to 70 km Mineral Composition: Some sedimentary and metamorphic rock. Mostly granite (igneous) The continental crust is older than oceanic crust OCEANIC CRUST 55% of surfarce More Dense (heavier): average density Thinner: 6 km, thinnest at Mid-Ocean Ridges Mineral Composition: some sediments (not sedimentary rock) and basalt (igneous) Oceanic crust is younger than continental crust (200 million years old or less) due to continuous recycling at subduction zones.
Earths Inner Core (comp., temp, pressure, density)
Inner Core - solid metal (iron and nickel, mostly) - temperature over 5000 K [sun's surface 5800 K] - pressure over 4 million atmospheres ("bars") - density over 10 g/cc
Why the numbers for Mars orbital rotation and axis inclination important?
Mars is smaller and, because of its greater distance from the Sun, cooler. It has seasons similar to Earth's because the tilt of its rotational axis (axial inclination) to the plane of its orbit about the Sun is about the same as Earth's. Interestingly, unlike Earth the significant eccentricity (elliptical shape) of the martian orbit means that the seasons on Mars are also affected by varying distance from the Sun.
Venus Properties
Mass: .82 Diameter: .95 Density (g/cc): 5.2 uncompressed: 4.3 Gravity: .91 Albedo:59% Amt. Pressure: 88 Temperature: 733 Thick carbon dioxide atmosphere; completely enveloped in thick clouds. Brightest planet as viewed from Earth; third-brightest object in Earth skies (behind Sun and Moon). Only visible mornings or evenings. Approximate twin for Earth in size but quite different in composition. Runaway "greenhouse effect" keeps surface temperatures above the melting point of lead. Planetary day longer than planetary year; retrograde ('backwards') rotation. Shows Moon-like phases visible in small telescopes.
Moon Properties
Mass: 0.01 Diameter: 0.27 Density (g/cc): 3.3 uncompressed: 3.3 Gravity: .17 Albedo: 11% Amt. Pressure: 0 Temperature: 93-403 Curious coincidence of size and distance causes Moon to appear roughly same size as Sun in Earth skies; causes beautiful solar eclipses. Much less dense than Earth. No significant atmosphere. Near side covered in large, lava-filled impact basins known as maria ("seas"). Recently mapped in detail by Clementine probe. First and so far only extraterrestrial body visited by humans (not counting Los Angeles or Toronto).
Mercury's properties
Mass: 0.06 Diameter: 0.38 Density (g/cc): 5.4 uncompressed: 5.2 Gravity: .38 Albedo: 12% Amt. Pressure: 0 Temperature: 103-623 Seen only in twilight, and only during brief periods of the year. Completes three rotations for every two revolutions about the sun. Gradual evolution of orbit served as a test of Einstein's Theory of General Relativity . Most notable feature is large Caloris Basin seen by space probes. Extremely tenuous atmosphere of gases captured from solar wind.
Mars Properties
Mass: 0.11 Diameter: 0.53 Density (g/cc): 3.9 uncompressed: 3.8 Gravity: .38 Albedo: 15% Amt. Pressure: 0.01 Temperature: 133-293 "Red Planet" appearance caused by significant surface concentrations of iron oxides (rust). Thin carbon dioxide atmosphere. Two tiny satellites, possibly captured asteroids. Much evidence of abundant surface water during early history. Caps of water ice and carbon dioxide ice at poles; seasonal changes. Subject to great dust storms esp. near perihelion. Presumed next planet to be visited by humans, perhaps by middle of next century.
Earth Properties
Mass: 1 Diameter: 1 Density (g/cc): 5.5 uncompressed: 4.4 Gravity: 1 Albedo: 39% Amt. Pressure: 1 Temperature: 183-333 Largest of the terrestrial (rocky) planets; largest planet in inner Solar System. Three-quarters of surface covered by water. Only planet in which water exists abundantly in all three states (solid, liquid, gaseous). Has second-largest satellite in terms of relative sizes (second to Pluto-Charon). Planet slightly oblate due to mass and rotation rate. Still geologically active (crustal activity, vulcanism). Nitrogen-oxygen atmosphere.
How does geological activity manifest itself (e.g., continental drift, volcanoes, earthquakes, mountain building)?
Most of the action is at plate boundaries. RIFT ZONES occur when plates are moving apart. New material is driven to the surface from below and cools into oceanic crust, driving the oceanic plates apart. Where an oceanic plate collides with a continental plate it is driven back into the mantle in a SUBDUCTION ZONE. When two oceanic plates collide, one is driven under the other in a similar fashion. When two continental plates collide, neither can subduct, so they both buckle up into a massive mountain range (e.g. the Himalayas). When two plates are moving laterally, the boundary is a FAULT ZONE (e.g. California). We can trace continental drift back in time at least 250 million years to a time when the continents were all in about the same place. This timescale is short compared to the 4.6 billion years since the earth formed. We discussed the past and future of plate tectonics on the Earth. Another interesting feature we discussed was "hotspots". The Hawaiian Island chain is a great example of what happens when a plate drifts over a hot spot. The cooling of the interior drives plate tectonics, which constantly changes the face of the Earth. Even more dramatic are the small scale changes caused by erosion, sedimentation, etc. These are due to the interaction of the hydrosphere and atmosphere with the Earth's crust.
What kinds of elements and compounds are found in Moon rocks? Which kinds are not found?
On the Earth, the most common rocks are sedimentary, because of atmospheric and water erosion of the surface. On the Moon there is no atmosphere to speak of and little or no water, and the most common kind of rock is igneous ("fire-formed rocks"). Geologically, the Lunar surface material has the following characteristics: Breccias, basalts, Anorthosite, which is a kind of igneous rock that forms when lava cools more slowly than in the case of basalts. This implies that the rocks of the Maria and Highlands cooled at different rates from the molten state and so were formed under different conditions. Lunar Soils contain glassy globules not commonly found on the Earth. These are probably formed from the heat and pressure generated by meteor impacts. The Anorthosites that are common in the Lunar Highlands are not common on the surface of the Earth (The Adirondack Mountains and the Canadian Shield are exceptions). They form the ancient cores of continents on the Earth, but these have largely been obliterated by overlying sedimentary deposits and by plate tectonic activity.
Earths Outer Core(liquid or solid, temp, present, densit, sour of magnet)
Outer Core - liquid metal - temperature ~ 4000 K - pressure less than inner core - density about 10 g/cc - source of magnetic "dynamo"
Study the different types of boundaries between crustal plates, know what sort of geological activity is associated with each, and be able to cite a real example or two of each
Plate boundaries are found at the edge of the lithospheric plates and are of three types, convergent, divergent and conservative. Wide zones of deformation are usually characteristic of plate boundaries because of the interaction between two plates. The three boundaries are characterized by their distinct motions. Divergent boundary, or spreading center. At these boundaries, two plates move away from one another. As the two move apart, mid-ocean ridges are created as magma from the mantle upwells through a crack in the oceanic crust and cools. This, in turn, causes the growth of oceanic crust on either side of the vents. As the plates continue to move, and more crust is formed, the ocean basin expands and a ridge system is created. Divergent boundaries are responsible in part for driving the motion of the plates. A convergent boundary or subduction zone. These are plate margins where one plate is overriding another, thereby forcing the other into the mantle beneath it. This causes form of trench and island arc systems. All the old oceanic crust is going into these systems as new crust is formed at the spreading centers. Convergent boundaries also explain why crust older than the Cretaceous cannot be found in any ocean basin-- it has already been destroyed by the process of subduction. Subduction zones are the location of very strong earthquakes, which occur because the action of the down going slab interacts with the overriding slab. The "Ring of Fire" around the margins of the Pacific Ocean is due precisely to the subduction zones found around the edges of the Pacific plate. Subduction also is the cause of the volcanic activity in places like Japan: as the downgoing slab goes deeper beneath the overriding plate, it becomes hotter and hotter because of its proximity to the mantle. This causes the slab to melt and form magma, which moves upward through the crust and eventually forms volcanoes (island arcs) in oceanic crust or huge intrusive masses (plutons and batholiths) in continental crust. The Aleutian Islands are another example of a surface expression of subduction. The third type of plate boundary is called a conservative or transform boundary. It is called conservative because plate material is neither created nor destroyed at these boundaries, but rather plates slide past each other. The classic example of a transform plate boundary is the San Andreas fault in California. The North American and Pacific Plates are moving past each other at this boundary, which is the location of many earthquakes. These earthquakes are caused by the accumulation and release of strain as the two plates slide past each other. Another example of a transform boundary is seen at the mid-ocean ridges, where the spreading centers are offset by transform faults anywhere from a few meters to several kilometers in length.
The rotational and orbital periods, the inclination of Mars' rotational axis?
Rotation Period: 24h36m The amount of time it takes for the planet to complete one full rotation on its axis. This leads us to an interesting point: Earth's rotation period is only about 23:56:04. You see, as Earth moves around the Sun in its orbit, the Sun slides slowly backward (relative to the stars) in the opposite direction from its daily East-to-West rise-to-set motion. Kind of like a salmon swimming against the current. So, the Earth has to spin a bit more to get the Sun to set. That's why a solar day is twenty-four hours long. Inclination of Orbit: 1.8° This describes the amount by which the planet's orbit is 'tilted' with respect to Earth's orbit. Because of Earth's orbital motion, the Sun appears to move through the stars, describing a circle over the course of a year. The apparent paths of the other planets will wander north or south of this line according to the relative tilts of their orbits versus Earth's. Orbital (Revolution) Period: 687d (1.8808y) The length of one of the planet's years, expressed in Earth days or Earth years, whichever is more convenient. Mercury and Venus, being closer to the Sun than Earth, have a shorter year; conversely, the rest of the planets, being farther from the Sun than Earth, have longer years. Inclination of Axis: 25.2° Indicates how much the planet is 'tilted' with respect to its orbit. On a planet whose axis tilted straight up from its orbit, the equator would naturally always be dead-level with the Sun. There would be no seasons, and day and night would be of equal length, everywhere on the planet, every day.
What are the overall "geographic" properties of Mars (e.g. polar caps, Tharsis bulge, giant shield volcanoes, runoff channels, overflow channels, cratered highlands, low-lying plains, wind-blown dust)?
Runoff Channels (rivers) - only in highlands - large area drainage + main channel + deposition - between 2 and 4 billion years ago, the climate was very different (liquid water flowed on its surface) it must have been warmer to have liquid water flowing on its surface • it has very little atmosphere now; it must have had a substantial one in the past • signs of volcanic activity are not that old, but no current activity/outgassing • Possibilities: - reverse RAGE (runaway icehouse effect) - impact - orbit changes - decreasing activity Weather on Mars is dominated by the north and south flow of carbon dioxide from pole to pole with the changing seasons. This can trigger planetwide dust storms. On Mars, a runaway icehouse effect resulted from weaker sun-light and the absence of plate tectonics. Water on Mars: Liquid water cannot exist on present- day Mars because the atmosphere is too thin and cold. But there is evidence for frozen water at the polar ice caps and beneath the surface of the regolith. Geological evidence from unmanned rovers shows that much of the Martian surface has been dry for billions of years, but some regions had substantial amounts of water.
What do we mean when we say a planet is "differentiated"?
The heavier elements sink to the center (the metal core).
What cases the Greenhouse effect? What would Earth be like without a greenhouse effect? Be familiar with a few examples of measured, recent changes in the atmosphere and climate. Be familiar with a few examples of human effects on atmosphere or climate on top of Earth's natural cycles
The "greenhouse effect" is widely discussed in the media, and although its details are complicated, its principles are not difficult to understand. Without a greenhouse effect, radiation from the Sun (mostly in the form of visible light) would travel to Earth and be changed into heat, only to be lost to space. This scenario can be sketched as follows: Sun's radiation → absorbed by Earth → Re-radiated to space as heat The greenhouse effect is a process where energy from the sun readily penetrates into the lower atmosphere and onto the surface of Earth and is converted to heat, but then cannot freely leave the planet. This can be sketched as follows: Sun's Radiation → absorbed by Earth → some re-radiated to space as heat → some trapped by the atmosphere Another way to think about the greenhouse effect is to consider that according to physics the radiation we receive from the Sun must be equally balanced by the heat Earth radiates out to space. If we were to give back less energy than we receive, our planet would soon be too hot for life. Likewise, if we were to give back more energy that we receive, our planet would soon be too cold for life. This can be written as a balanced equation of radiation: Solar radiation input to Earth = Earth's output of re-radiated heat If we were to measure the temperature of the Earth from space, the Earth's "surface" would show a temperature appropriate for this requirement of energy balance: a measurement of roughly -18 degrees Celsius (about 0 °F). At this temperature, our planet radiates a quantity of heat into space that is equivalent to the amount of energy received from the Sun. At this point you may be asking how we can speak of "global warming" when we have just stated that the Earth (as seen from space) MUST stay at the same temperature? And how is it that the temperature of the Earth's surface is only a chilly 0°F? The key to understanding this apparent contradiction is to remember that we live at the bottom of the atmosphere. As far as the radiation balance is concerned, the lower atmosphere and the surface of Earth form part of a "warm interior" of the planet.
How does the atmosphere of Mars differ from that of Earth and Venus?
The Earth's atmosphere is a complex collection of gases, mixed with water vapor, that provide the requisite conditions for living things. Earth's animal and plant life would have little chance for survival in the atmosphere of Mars or Venus. Mars' atmosphere is both shallow and thin, less than 1% as dense as Earth's. Even if liquid water were present (which it is not), the atmosphere cannot hold any appreciable water vapor. Much of Mars' oxygen is locked into surface rocks, and the remainder is combined as carbon dioxide. While CO2 makes up 95% of the Martian atmosphere, the low pressure means insufficient concentrations to support Earth vegetation. And while Martian temperatures may reach 20°C (68°F) in the Martian summer, it can also be as low as -140°C (-220° F). The atmosphere is highly inefficient at heat transfer. Venus is the other extreme of conditions. While Mars' atmosphere is cold and rarified, Venus' is hot and dense. The same net result is the absence of liquid water or vapor transport. Also the same is the predominance of carbon dioxide, with much less nitrogen than Earth. The temperature and pressure of Venus are much greater than Earth : the surface pressure is 92 times as great, and temperatures average 460°C (770° F). The atmospere is highly efficient at heat transfer, so there are few places on the surface more than a few degrees cooler. The only "rain" is droplets of sulfuric acid in high Venusian clouds of sulfur dioxide.
Earths Crusts
The Earth's surface consists of two types of crust: OCEANIC and CONTINENTAL. They are very different. The oceanic crust is young, thin, and dense. The continental crust is older, thicker, and less dense. They both float on a semi-solid asthenosphere between the crust and the mantle. Continents build up thicker and float higher. About 55% of the Earth's surface is covered by oceanic crust (the oceans cover some of the continental crust). The Earth's surface is broken up into 6 major and about 10 smaller plates. There is no dead space between the plates, but they are always in motion. Geological activity is primarily concentrated along plate boundaries, where they are bumping into each other, being driven apart from each other, or scraping along each other. Most of the action is at plate boundaries. Figure 9-14 from your text will give you great insight into the world's "hot spots". RIFT ZONES occur when plates are moving apart. New material is driven to the surface from below and cools into oceanic crust, driving the oceanic plates apart. Where an oceanic plate collides with a continental plate it is driven back into the mantle in a SUBDUCTION ZONE. When two oceanic plates collide, one is driven under the other in a similar fashion. When two continental plates collide, neither can subduct, so they both buckle up into a massive mountain range (e.g. the Himalayas). When two plates are moving laterally, the boundary is a FAULT ZONE (e.g. California). We can trace continental drift back in time at least 250 million years to a time when the continents were all in about the same place. This timescale is short compared to the 4.6 billion years since the earth formed.
basalt
The Maria are mostly composed of dark basalts, which form from rapid cooling of molten rock from massive lava flows.
How does the atmosphere of Venus differ from that of the Earth?
The atmosphere of Venus is so harsh that it is the main reason that no one has ever been able to make optical observations of anything other than the planet's upper atmosphere. The next challenge that the atmosphere of Venus presents is its composition. It is made up of 96% carbon dioxide. Oxygen can not be detected even as a trace element. At the surface the atmospheric pressure is 92 times that of Earth. If you were able to find a way to survive the intense pressure and had enough oxygen, you would be standing on a surface that is hot enough to melt lead. The temperature across Venus, from pole to pole, is a steady 462°C as a result of the atmosphere's greenhouse qualities. In the hottest parts of the hottest deserts here on Earth, the temperatures never top 50°C.
What are the critical steps involved in the "runaway greenhouse effect" that could be responsible for the high surface temperature on Venus?
The explanation for the extremely high surface temperatures on Venus is attributed to the greenhouse effect. The nearly transparent atmospheres of Earth and Mars allow much of the heat received from the Sun to escape, by being reflected or reradiated into space. But on Venus, carbon dioxide and sulfuric acid in the atmosphere absorb much of this reflected energy. The energy is eventually reemitted but not until the surface is much warmer than it would be in the absence of CO2. In essence, Venus is like a well-insulated house in the winter. This planetary greenhouse entraps heat received from the Sun and distributes it planetwide so there are no cold polar zones as on Earth and Mars (Figure 7.13). The temperature anomaly is particularly striking because due to Venus's reflective cloud cover, the surface of Venus actually receives less solar energy directly from the Sun than Earth does. start with water and lower temperature on Venus (Sun's luminosity was lower) • raise temperature a little --> H20 evaporates • water vapor is a greenhouse gas, so temperature goes up • this causes more water to evaporate, which releases dissolved CO2 and more H20 vapor (positive feedback loop) • H20 gets to upper atmosphere, where solar ultraviolet breaks it apart • Hydrogen --> space; O --> rocks, etc • D/H ratio confirms that this happened on Venus • Could it happen to us? (yes, and it will, eventually)
Near side
The face of the Moon turned toward us is termed the near side (image at right). It is divided into light areas called the Lunar Highlands and darker areas called Maria (literally, "seas"; the singular is Mare). The Maria are lower in altitude than the Highlands, but there is no water on the Moon so they are not literally seas (Recent evidence from the Clementine spacecraft suggests that there may be some water on the Moon, contrary to previous assumptions). The dark material filling the Maria is actually dark, solidified lava from earlier periods of Lunar volcanism. Both the Maria and the Highlands exhibit large craters that are the result of meteor impacts. There are many more such impact craters in the Highlands.
How do the craters on Venus differ from those on other planets and the Moon (no small ones, all are nearly pristine)?
The lack of water on the surface has important implications for the evolution of Venus. The important role of water and ice in shaping the surface of Earth cannot be understated. Movement of water occurs continually through an extensive, well-integrated system of oceans, rivers, lakes, and glaciers to produce an endless variety of landforms and rock types. Many common rocks on Earth---shales, sandstones, and limestones---owe their existence to some portion of the hydrologic system. Water and ice were also important in shaping the geologic evolution of Mars, as evidenced by the rampart craters, ancient streams, and huge channels produced by catastrophic floods. However, Venus lacks these surface features and rocks produced by water. No evidence of ancient water-related landforms has yet been found on Venus within the limits of resolution on the available radar images. At present, Venus is far too hot for water to exist either as a liquid or a solid, so water cannot now be a major geologic agent there.
How do we know that impacts were more frequent on the Moon (and presumably also on the Earth) early in the history of the solar system?
The lunar highlands are more heavily cratered than the lunar maria, and the maria were formed shortly after the highlands
far side
The side of the Moon unseen from the Earth is called the far side. One of the discoveries of the first Lunar orbiters is that the far side has a very different appearance than the near side. In particular, there are almost no Maria on the far side, as illustrated in the image shown to the left of a portion of the far side surface. In this figure a number of meteor impact craters are visible.
The difference between conduction, convection, and radiation of heat?
Transmits the heat energy to atoms next to them to even out the temperature. The earth gains little from conduction it's mostly radiation that helps us function and keeps us warm Convection is the movement of heat in liquids and gasses to even out the temperature fastest. This process is called diffusion; It's a flow of particles cold and hot in a fluid. Makes up the weather and how we measure the pressure of the air and the temperature. convection is how heat goes into the atmosphere Heat transfer by radiation, which occurs in any transparent medium (solid or fluid) but may also even occur across vacuum (as when the Sun heats the Earth). Radiation is the transfer of energy through space by means of electromagnetic waves in much the same way as electromagnetic light waves transfer light. The same laws that govern the transfer of light govern the radiant transfer of heat.
Why are the mountains so tall on Mars?
Ultimately, volcanic mountains on Mars are higher because they have more time to grow. The lack of plate tectonics that allowed this unhindered flow also prevented massive pressure buildups that would have blown the top off of the volcano, decreasing its overall height.
How can we determine the ages of the lunar highlands and the lunar maria?
We were able to use radioactive dating to determine the ages of rocks brought back from both types of regions by the Apollo astronauts.
What is the fundamental cause of geological activity?
When the pressure is low and the temperature is high, even the solid rock in the mantle can "flow", so we expect the outer part of the mantle to be convecting. This drives all of the action we see on the surface of the Earth. • earthquakes, volcanoes (several types), mountains (several types), island chains • constantly changes Earth's surface • nothing left of "original" surface • driven by heat from Earth's interior • plate boundaries : where the action is
Which of the following statements best describes the relative amounts of the two kinds of crust ("oceanic" and "continental") making up the Earth's solid surface?
a little more than half the Earth's crust is oceanic
The lunar highlands
are older and more heavily cratered than the lunar maria.
Rocks that are formed when magma, or lava, "freezes" from a liquid to a solid.
igneous
The "back side" of the Moon (the half that is never seen from Earth)
is almost entirely composed of highlands.
You should have a feel for how Venus' global properties compare with the other terrestrial planets (especially Earth) and Why are these last 3 properties so different from those of the Earth?
mean density, diameter, albedo (75%), surface temperature (750 K), and atmospheric pressure (90 times that of Earth). Because of the distance from the sun and the volcanic activity. Visualization of the planet is made impossible be the high amounts of sulfuric acid in the atmosphere. Clouds in the upper atmosphere are full of sulfuric acid droplets. Sulfur is highly reflective of visible light, thus preventing observation much deeper than the upper limits of the clouds themselves.
Can be formed when one of the two types above are slowly changed under conditions of high temperature and/or high pressure.
metamorphic
Mercury
planet closest to the Sun; has a thin atmosphere with temperature extremes, an iron core, and many craters and high cliffs
What can we learn by comparing the density of craters (number per square kilometer on the surface) in the highlands and in the maria? How can impact craters be used to determine the age of a planetary surface? What can we learn by studying the distribution of crater sizes?
relative age of surface (how long has it been exposed) • rate of cratering as a function of time (is it constant?) • rate of erosion, if any (on Moon: eroded by other impacts, lava flows, rock slides, etc; NOT by weathering) from crater density/current impact rate, age of maria: 3.5 to 4 billion years highlands: older than this, but younger than 4.6 billion years
Rocks formed by slowly building up material that has been eroded away by wind or water
sedimentary
Runaway Greenhouse Effect (RAGE)
start with water and lower temperature on Venus (Sun's luminosity was lower) • raise temperature a little --> H20 evaporates • water vapor is a greenhouse gas, so temperature goes up • this causes more water to evaporate, which releases dissolved CO2 and more H20 vapor (positive feedback loop) • H20 gets to upper atmosphere, where solar ultraviolet breaks it apart • Hydrogen --> space; O --> rocks, etc • D/H ratio confirms that this happened on Venus • Could it happen to us? (yes, and it will, eventually)
what can the presence of a magnetic field tell us about the interior?
that is has a liquid and metal conducting interior that is rapidly rotating- indicating an electrical conductor in motion, like the liquid outer core of the Earth
Why doesn't the Moon have a permanent atmosphere (gravity only 1/6 that of the Earth)?
the Moon is often considered to not have an atmosphere, as it cannot absorb measurable quantities of radiation, does not appear layered or self-circulating, and requires constant replenishment given the high rate at which the atmosphere is lost to space (solar wind and outgasing are not primary components of the Earth's, or any stable atmosphere yet known). Because the moon has less mass than Earth, the force due to gravity at the lunar surface is only about 1/6 of that on Earth.
breccia
which are fragments of different rocks compacted and welded together by meteor impacts, are found in the Maria and the Highlands, but are more common in the latter.
why are conduction, convection, and radiation of heat important throughout the Earth's interior and surface layers?
• Temperature is a measure of internal energy (kinetic and potential) • Heat is "flow" of thermal energy from high temperature to low temperature
