Lec 14 Flashcards

Question

basic requirements for a global magnetic field

Answer 1

1. An interior region of electrically conducting fluid (liquid or gas), such as molten metal 2. Convection in that layer of fluid 3. At least moderately rapid rotation

Answer 2

Earth is the only terrestrial world that meets all three requirements, which is why it is the only terrestrial world with a strong global magnetic field. The Moon has no global magnetic field, presumably because its core has long since cooled and ceased convecting. Mars’s core probably still retains some heat, but not enough to drive core convection, which is why it also lacks a global magnetic field today. Venus probably has a molten core layer much like that of Earth, but either its convection or its 243-day rotation period is too slow to generate a magnetic field

Answer 3

Impact cratering: the creation of bowl-shaped impact craters by asteroids or comets striking a planet’s surface Volcanism: the eruption of molten rock, or lava, from a planet’s interior onto its surface Tectonics: the disruption of a planet’s surface by internal stresses Erosion: the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

Answer 4

The crater in has an extra large bump in its center and appears to be surrounded by mud flows, suggesting that underground water (or ice) melted or vaporized on impact; the muddy debris then flowed across the surface and hardened into the pattern we see today

Answer 5

shows obvious signs of erosion: It lacks a sharp rim and its floor no longer has a well-defined bowl shape. This suggests that ancient rainfall eroded the crater and that the crater bottom was once a lake

Answer 6

Volcanism occurs when underground molten rock finds a path to the surface. -molten rock tends to rise for three main reasons. 1), it’s generally less dense than solid rock, and lower-density materials tend to rise when surrounded by higher-density materials. 2), the solid rock surrounding a chamber of molten rock can squeeze the molten rock, driving it upward under pressure. 3), molten rock often contains trapped gases that expand as it rises, which can make it rise much faster and lead to dramatic eruptions. The result of an eruption depends on how easily the molten rock, or lava, flows across the surface.

Answer 7

The thickest lavas cannot flow far before solidifying and therefore build tall, steep-sided volcanoes (technically called stratovolcanoes) -examples include Mount Fuji (Japan), Mount Kilimanjaro (Tanzania), and Mount Hood (Oregon). --the thick lava can allow particularly great pressure to build up in these volcanoes, making them prone to explosive eruptions that can deposit debris over vast areas. Somewhat runnier lavas can spread some distance before they solidify, creating volcanoes that slope more gradually (technically called shield volcanoes) --these volcanoes can be very tall but are not very steep -e.g. mountains of the Hawai‘ian Islands on Earth and Olympus Mons on Mars The runniest lavas flow far and flatten out before solidifying, creating vast volcanic plains --e.g. include lava plains that make up the Columbia Plateau in Washington and Oregon and vast lava plains that make smooth regions (maria) on the Moon

Answer 8

The water and gases from these planetesimals became trapped in the interiors of the planets in much the same way that the gas in a carbonated beverage is trapped in a pressurized bottle. Volcanic eruptions can release this gas in a process known as outgassing, which occurs both with dramatic volcanic eruptions and with the more gradual escape of gas from volcanic vents

Answer 9

While at least some tectonic activity has occurred on every terrestrial world, it has been particularly important on Earth, where the ongoing stress of mantle convection fractured the lithosphere into more than a dozen pieces, or plates These plates move over, under, and around each other in a process we call plate tectonics

Answer 10

refers to the breakdown or transport of surface rock through the action of ice, liquid, or gas Note that while we usually associate erosion with breakdown, sand dunes and river deltas are examples of features built up by erosion. erosion has built much of Earth’s surface rock: Over long periods of time, erosion piled sediments into layers on the floors of oceans and seas, forming sedimentary rock. The layered rock of the Grand Canyon is an example, built up long before the Colorado River carved the canyon.

Answer 11

We can estimate the geological age of any surface region from its number of impact craters, with more craters indicating an older surface. By “geological age” we mean the age of the surface as it now appears: --a geologically young surface is dominated by features that have formed relatively recently in the history of the solar system, while a geologically old surface still looks about the same today as it did billions of years ago. To understand the idea, recall that all the planets were hit by impacts during the heavy bombardment that ended almost 4 billion years ago, but fewer impacts have occurred since. In places where we see numerous craters, such as on much of the Moon’s surface, we must be looking at a surface that has stayed virtually unchanged for billions of years. A surface can have fewer craters only if the scars of ancient impacts have been erased over time by other geological processes, such as volcanic eruptions or erosion

Answer 12

In the lunar highlands, craters are so crowded that we see craters on top of other craters.

Answer 13

In the lunar maria, we see only a few craters on top of generally smooth volcanic plains

Answer 14

tells us that the four processes don’t always affect worlds in the same way. For example, Earth has far more features of erosion than any of the other terrestrial worlds. Ultimately, we can trace the answer back to three fundamental planetary properties: size, distance from the Sun, and rotation rate

Answer 15

Tectonics Volcanism and tectonics both require internal heat, which means they depend on planetary size. --larger planets have more internal heat and hence more volcanic and tectonic activity. All the terrestrial worlds probably had some degree of volcanism and tectonics when their interiors were young and hot. --as an interior cools, volcanic and tectonic activity subsides --the Moon and Mercury lack ongoing volcanism and tectonics because their small sizes allowed their interiors to cool long ago. Earth has active volcanism and tectonics because it is large enough to still have a hot interior. Venus, nearly the same size as Earth, must still be hot inside and probably also has active volcanism and tectonics. Mars, with its smaller size, has much less volcanism and tectonic activity today than it did in the distant past.

Answer 16

Erosion arises from weather phenomena such as wind and rain --shows that erosion therefore has links with all three fundamental planetary properties. Planetary size is important because erosion requires an atmosphere, and a terrestrial world can have an atmosphere only if it is large enough to have had significant volcanic outgassing and if its gravity is strong enough to have prevented the gas from escaping to space. Distance from the Sun is important because of its role in temperature: If all else is equal (such as planetary size), the higher temperatures on a world closer to the Sun will make it easier for atmospheric gases to escape into space, while the colder temperatures on a world farther from the Sun may cause atmospheric gases to freeze out. Distance is also important because water erosion is much more effective with liquid water than with water vapor or ice and therefore is strongest when moderate temperature allows water vapor to condense into liquid form. Rotation rate is important because it is the primary driver of winds and other weather: -faster rotation means stronger winds and storms. The Moon and Mercury lack significant atmospheres and erosion because they lack outgassing today, and any atmospheric gases they had in the distant past have been lost to space

Answer 17

Impacts are random events and therefore the creation of craters is not “controlled” by fundamental planetary properties --however, because impact craters can be destroyed over time, the number of remaining impact craters on a world’s surface is controlled by fundamental properties. The primary factor is size: Larger worlds have more volcanism and tectonics (and in some cases erosion), processes that tend to cover up or destroy ancient impact craters over time. Mercury and the Moon are heavily cratered today because their small sizes have supported relatively LITTLE geological activity, so we can still see most of the impact craters that formed during the heavy bombardment. Mars has had more geological activity and therefore has somewhat fewer impact craters remaining today. The active geologies of Venus and Earth have erased nearly all ancient craters, leaving only those that have formed relatively recently (within the last billion years or so)

Answer 18

Their small sizes mean that most of their internal heat was lost long ago, leaving them without significant ongoing volcanism or tectonics. Small size also explains their lack of significant atmospheres and erosion: Their gravity is too weak to hold gas for long periods of time, and without ongoing volcanism they lack the outgassing needed to replenish gas lost in the past. This overall lack of geological activity means they still retain the scars of ancient impacts, explaining why their surfaces are heavily cratered. Still, both worlds should have had hot interiors early in their histories, which explains why they also show a few features attributable to past volcanic and tectonic activity

Answer 19

Volcanism and Tectonics in the Lunar Maria -shows how the maria probably formed -during the heavy bombardment, craters covered the Moon’s entire surface -the largest impacts were violent enough to fracture the Moon’s lithosphere beneath the huge craters they created -although there was no molten rock to flood the craters immediately, the ongoing decay of radioactive elements in the Moon’s interior ultimately built up enough heat to cause mantle melting --molten rock then welled up through the cracks in the lithosphere, flooding the largest impact craters with lava

Answer 20

the maria are generally circular because they are flooded craters (and craters are almost always round), and they are dark because the lava consisted of dark, dense, iron-rich rock (basalt). The flat surfaces of the maria tell us that the lunar lava spread easily and far, which means that it must have been among the runniest lava in the solar system. It was so runny that in places it flowed like rivers of molten rock, carving out long, winding channels. The relative lack of craters within within the maria is a consequence of the fact that the lava floods occurred after the heavy bombardment subsided, and relatively few impacts have occurred since that time.

Answer 21

impact craters and volcanism on mercury -Mercury’s craters are less crowded together in many places than the craters in the most ancient regions of the Moon, suggesting that molten lava later covered up some of the craters that formed on Mercury during the heavy bombardment. -Although we have not found evidence of lava flows as large as those that created the lunar maria, the reduced crater crowding and the many smaller lava plains suggest that Mercury had at least as much volcanism as the Moon --many of the large craters have few craters within them, indicating that they must have formed at a time when the heavy bombardment was already subsiding. Tectonic Evidence of Planetary Shrinking -They probably formed when tectonic forces compressed the crust, causing the surface to crumple. -Because crumpling would have shrunk the portions of the surface it affected, Mercury as a whole could not have stayed the same size unless other parts of the surface expanded. -However, we find no evidence of large-scale “stretch marks” on Mercury -possible that whole planet shrunk --Mercury therefore gained and retained more internal heat from accretion and differentiation than the Moon, and this heat caused Mercury’s core to swell in size -Later, as the core cooled, it contracted by perhaps as much as 20 km in radius -The mantle and lithosphere must have contracted along with the core, generating tectonic stresses that created the great cliffs

Lec 14 Flashcards

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