geoscience10
Science professors teach certain theories and not others (Newton's physics, and not Aristotle's, or Darwin's evolution and not Lamarck's). If you were to ask the professors why, a majority would tell you (more or less; not using exactly these words but with this meaning):
"Nature has repeatedly been asked (through experiment) which is better, and we are teaching the ones that made successful predictions, and not teaching the ones that failed. You can be quite confident that the big-picture items in science class have been tested against reality and found to work. There still might be someone in academe who would reply with B (your professors remember a couple of their professors who could have said such a thing) (the technical term for anyone who would reply with the quote in B is "jerk"), but that is pretty rare today.
Look at the picture above. What happened here?
A great volcanic explosion occurred, spreading material across the landscape, and the hole left behind after the eruption later filled with water. Nature has many ways to make holes, and many other ways to make mountains. Part of this class is learning to read the clues, just as geologists do. We saw at Death Valley that the faults tend to make straight lines. Streams on glaciers are not nearly this big, nor are river bends. This is the crater of Crater Lake, almost 2000 feet deep and 6 miles across, left by the cataclysmic eruption of Mount Mazama in Oregon.
Volcanoes of many different types can be observed at the surface of the Earth. Suppose you are looking at a hot-spot volcano. If you could see deep beneath that volcano, what would you find?
A rising tower of hot rock, coming up from below and perhaps from waaaaay below, down at the bottom of the mantle. Earthquakes make sound waves that go through the whole Earth, and go slower through hotter, less-dense rocks. By setting out listening devices called seismometers around the Earth, and listening to the waves from many earthquakes in many places, scientists can map the hotter regions, and find that towers of hot rock come up from way deep in the Earth in some places. But, some other hot spots, while clearly coming up from below, don't seem to start quite as deep.
Look at the picture above. What type of volcano is this?
A subduction-zone-type, steep andesitic stratovolcano This is Lassen Peak in Lassen Volcanic National Park, northern California. Lassen erupted between 1914 and 1921, near the south end of the Cascades chain of subduction-zone volcanoes, and was made a national park in 1916. Hot-spot volcanoes aren't as steep, plateau basalts cover state-sized areas with very flat-lying flows, cinder-cone volcanoes are much smaller, and George's piles are smaller yet.
The peer review process, in which scientists submit write-ups of their ideas and experiments to a set of colleagues who judge how good the ideas are before the ideas can be published, is:
A useful and important, even if imperfect, mechanism of quality-control for the scientific literature. The peer review process applies to scientific publications and works like this: I get an idea and do some experiments to test it and write down the results of the tests. I send the paper to a scientific journal (Nature, Journal of Geophysical Research, etc.) and the editor of the journal sends it to a number of other scientists who can best judge whether my methods are good, whether my results are new and interesting, and whether my paper ought to be published. They don't base their judgements on whether they like me or not or whether I'm a nice guy/gal or not (or at least they ought not base their judgments on that, though it does happen: we're human!). They don't base their judgements on whether my ideas are popular or unpopular. They are only supposed to ask: is this really new (i.e., did somebody else think of this and publish it already somewhere else?) and are the methods used accurate and repeatable?
You get some stuff, and start taking it apart. But, you are restricted to the use of "ordinary" means (fire, sunlight, your digestive system) and you cannot use atom smashers or atom bombs. What is the smallest piece that you are likely to be able to produce:
An atom We can break matter down into atoms (Greek for "not cuttable" because the Greeks didn't have atom smashers or other exotic tools that would allow cutting atoms into smaller pieces). All of the wrong answers here are smaller pieces of atoms, but cannot normally be isolated by "ordinary" tools.
The picture above shows Telescope Peak, towering above Death Valley.The straight edge of the alluvial fan in the foreground is:
An earthquake fault, where the valley has dropped relative to the mountains. The valley is still dropping along earthquake faults as the mountains move away from the valley center. Straight-line faults really do exist. The "famous" Zabriskie Point Highway does not exist, although you can drive out there; given the vast flat expanse of the bottom of Death Valley, the park service would not have excavated to build a highway, choosing instead to save a few tens of millions of dollars by just putting the highway on the flat valley floor.
National Parks are
An invention of the United States that has spread around much of the world, as a way of protecting some of the finest parts of the world. Yellowstone was the first National Park, but now you can find National Parks scattered across the planet, preserving key areas for the enjoyment of this generation and for future generations.
Most earthquakes:
Are caused when rocks on opposite sides of a break, or fault, in the Earth's crust move in different directions, and the fault is poorly lubricated, so the rocks along the fault get stuck for a while and bend their neighbors before breaking free and moving There may be "implosion" earthquakes, but they are rare. Some breaks in the crust are well-lubricated and don't make earthquakes. If rocks on opposite sides of a break move in the same direction at the same speed, then there will be no relative motion between those rocks, and they won't make earthquakes. But when rocks try to move in opposite directions but are stuck, they bend like springs and then break, shaking things and knocking them down in an earthquake. And Diet Coke drinkers who have not yet had their caffeine are unlikely to be sufficiently agitated to kick the Pepsi machines hard enough to make the larger earthquakes that are observed.
The deepest earthquakes are rare, and differ in some ways from the more-common type of quakes. These deepest earthquakes probably:
Are the shaking of the ground caused by "implosion" as minerals rearrange to denser forms as the pressure on them rises in downgoing slabs. "Implosion" is the currently favored idea. As subduction zones take rocks deeper where pressure is higher, the building blocks tend to reorganize to take up less space, shifting from, say, a one-on-top-of-another pattern to a fit-in-the-space-between-those-below pattern. Sometimes, this seems to be delayed and then to happen all at once (I can't move until my neighbor does...), giving an implosion. The biggest, deepest earthquakes happen where temperatures and pressures are so high that we don't think rocks can break. Humans have never made a hole anywhere nearly as deep as the deeper earthquakes. We have mostly quit testing atomic bombs. And, a big earthquake is way bigger than a big atomic bomb. And, no one has ever put a soda machine deep enough to account for the deepest earthquakes.
The above diagram is from one of the Geomations in the unit. It shows three possible fault styles. A and B are cross-sections, with a collapsed building on top to show you which way is up—the yellow band is a distinctive layer of rock that was broken by the earthquake that also knocked down the building. C is viewed from a helicopter, looking down on a road with a dashed yellow line down the middle; the road was broken by an earthquake along the green fault, and the earthquake knocked down a building to make the funky-looking brown pile in the upper right.What is accurate about the different earthquake styles?
B is pull-apart, C is slide-past, and A is push-together Imagine putting the image on paper, cutting out the blocks (one block on each side of the fault), and then sliding them back together to make the original, unbroken features. A and B stand up from the table, C lies down on the table. Now, slide them to make the picture as seen here. In A, you'll be moving the right-hand block up and toward the other block, so it is push-together. In B, you'll be moving the right-hand block down and away from the other block, so it is pull-apart. And in C, you'll slide one past the other (geologists distinguish right-lateral and left-lateral motion for C, but you don't have to worry about that much detail).
Convection occurs:
Because hotter things are less dense and tend to rise. Almost everything expands from heating, taking up more space with the same weight and so becoming less dense. Gases, liquids, and sufficiently soft solids can convect if heated from below, with warming of the lower layer causing it to rise.
Tsunamis:
Can be predicted with some accuracy seconds to hours before the waves strike in most cases, allowing quick warnings to save many lives. Because tsunamis are triggered by earthquakes, among other things, and we cannot predict earthquakes accurately, we cannot make months-in-advance predictions of tsunamis. The p-waves from the earthquakes that cause the most common tsunamis move more rapidly than the tsunamis do, allowing timely warnings; however, because the tsunamis get where they are going in hours or less typically, not much time is available. Water does go out before rushing in along some coasts, but comes in before going out along other coasts, waves have "up" and "down" parts, and some coasts get an "up" first while other coasts get a "down" first. Little earthquakes make little tsunamis; big earthquakes make big tsunamis.
The great disaster at Lake Nyos in Cameroon, Africa, in which hundreds of people died, occurred when this material was released from the volcano:
Carbon dioxide (CO2) that suffocated the people. Lake Nyos is in a volcanic crater. CO2 seeped into the lake and built up at depth within the lake. For some reason (earthquake or landslide) the lake was disturbed and vast quantities of CO2 were released, suffocating residents near the lake.
Heat is moved around by convection, conduction and radiation (and by lemmings carrying space heaters, if lemmings ever carry space heaters). Which statement is more nearly correct?
Convection moves heat efficiently through the soft, hot rocks of the Earth's mantle, but is not efficient at moving heat through the space between the Sun and the Earth. Heat from deep in the Earth is moved up through the soft bulk of the planet primarily by convection, but convection of rocks certainly does not continue beyond the planet, where radiation becomes dominant. In the shallowest, uppermost layers of the Earth, most of the heat transfer is by conduction. And the poor lemmings deserve a rest and a snack.
The processes that made Death Valley continue to operate today. For this question, ignore the sand and gravel moved by water and wind, and think about the big motions of the rocks beneath. Choose the best answer: what are they doing to the valley?
Death Valley is getting wider and deeper. The pull-apart action that is spreading Death Valley and surroundings also involves uplift of mountains or downdrop of valleys, and Death Valley has dropped as its flanking mountains have moved apart.
Subduction zones produce an amazing variety of geological features. These include:
Deep trenches in the sea floor, formed by the bending of the downgoing plate, and sometimes filled with sea water but sometimes filled with sediment eroded from nearby land. The deepest spots in the ocean are formed when downgoing slabs are bent downward to make deep trenches parallel to the shore. However, sometimes these trenches become sediment-filled. Microsoft CDs are a relatively small part of that sediment. Rivers don't cut below sea level, and glaciers flowing away from the coast cannot cut a huge trench parallel to the coast.
The volcanoes of the island of Hawaii eventually will:
Drift off the hot spot and cease to erupt, while a new volcano grows to their southeast. As they drift off the hot spot, the Hawaiian chain volcanoes lose their source of melt and quit erupting. But, a new volcano grows. Indeed, the new one, Loihi Seamount, is already there and erupting underwater, building toward the surface. As they cool and sink, and are eroded, the Hawaiian volcanoes disappear below sea level. Hawaiian volcanoes are "friendly", not having highly explosive eruptions. Yellowstone is an anomaly; the hot spot is not making a huge amount of melt, and that melt is modified in coming through the continent, so Yellowstone explodes despite being a hot spot. But most hot-spot volcanoes are not highly explosive. The "protective" layer of condominiums is developing in parts of Hawaii, but lots will happen to the volcanoes in addition—earthquakes and eruptions and drifting and more—and wait until next time when we learn about sides falling off!
Look at the picture above, from the coast of Olympic National Park. What happened here?
Earthquakes knocked loose undersea muds that raced down the slopes of the west coast into the subduction zone, making rocks that were then scraped off the downgoing slab to make part of Olympic National Park. Olympic is the pile of scraped-off stuff, and some of it fell into the trench rather recently during earthquakes. There really are volcanic layers, and they can be sorted by size, but soils tend to form between the eruptions, and the different eruptions will make different-looking layers. There is a little bit of grooving across the rock face, from waves hitting the rock and some layers being softer than others, but this is a very non-glacial-looking deposit. Amazing numbers of pocket knives and other items are confiscated at airports, often from absent-minded geologists, but the government agents don't litter with those confiscated items. Airline toilets flush into holding tanks on the plane, not onto people or rocks below, and very rarely have pocket knives because the knives are confiscated first.
Hot spots:
Feed basaltic volcanoes (composition similar to sea floor), unless the hot spot is altered in composition coming through a continent, in which case the volcano may be more andesitic. The rising hot rock of hot spots feeds volcanoes. Both sea floor and hot-spot volcanoes come from melting a little of the very-low-silica mantle, pulling out the melt, and freezing it, and so are basaltic (low-silica) volcanoes. Note, though, that a few hotspots (such as Yellowstone) are not basaltic, because the basalt has been altered in getting through the continent. The melt probably started out as something that would make basalt, and indeed, the Yellowstone hot-spot track includes basaltic lavas such as those at the glorious Craters of the Moon National Monument. The hot-spot lavas are runny, and spread easily under the air to make volcanoes with gradual slopes, unlike the steep stratovolcanoes, although the slopes of hot-spot volcanoes are steeper under water because the water cools the lava so rapidly that it can't spread far.
Your job depends on you finding the best available information on a particular technical topic. Where should you concentrate your search if you want to do it right and keep your job?
Find and study refereed scientific articles in learned journals. No source of information is perfect, but the refereed articles in learned journals put immense effort into "getting it right". The web has reliable information, of course, but probably most of the information on the web is not especially reliable. The web is very inexpensive, and lots of people put junk on it. Think tanks also often are pushing an agenda, and try to "spin" information their way. Most newspapers are around for the long haul, and try to make the news fairly accurate, although some newspapers do have agendas, and the editorial pages are not especially accurate. But, if the report is on the views of a public figure, the newspaper may accurately report what the public figure said, but what the public figure said may be less than completely accurate. Some magazines are quite good and careful, but many are pushing a belief or just overhyping things to tease you into buying the magazine. And while you are welcome to believe that drinking a particular cola makes you sexy, or makes your favorite candidate sexy... don't count on it.
The law that established the National Parks gave them a hard job, because it required that they:
Help people enjoy the parks today, but also save the parks for the future The law that established Yellowstone as the first national park required "conservation... unimpaired for...future generations" and "to provide for the enjoyment" of the parks. But what if so many people want to visit that they scare the wolves, or trample the soil and kill the roots of the big trees? Enjoying and preserving at the same time isn't easy!
You hear an astronomer on the evening news, pointing out a coming alignment of planets and predicting that the extra gravitational attraction is sure to trigger a huge earthquake in California during the few hours of alignment. Based on what has been covered in this class, a reasonable approach is to:
Ignore it; although gravitational forces such as tides and planetary pulls might possibly exert a very small effect on earthquakes, no one has successfully predicted the where-and-when of earthquakes. By keeping track of where earthquakes happen, combing written and oral histories of past earthquakes, looking at geological deposits to see where shaking has occurred and broken rocks or tree roots or caused sand boils, and measuring where rocks are moving and where they aren't, good estimates can be made of earthquake hazards; but, we can't figure out exactly when the next quake will hit. Planetary-alignment predictions have been made, and have failed miserably. The tiny effect of gravity of the planets on the Earth has not been shown to affect earthquakes at all, although it remains possible that some very small influence exists.
You get in your Magic School Bus, drive down the throat of a volcano, and find that you are driving through melted rock that does not make lumps but flows more easily than does most melted rock. It is likely that the melted rock you are driving through:
Is especially rich in water and carbon dioxide compared to most melted rocks The silicon-oxygen tetrahedra link up to make lumps, so anything that gets in the way of this linking will oppose lumping. Iron, water, carbon dioxide, or high heat that shakes the lumps apart can all oppose the lumping of polymerization.
What is accurate about peer review of scientific papers?
It provides quality control by eliminating many mistakes. Reviewers work hard to identify errors of any sort, almost always identify many, and then the reviewers and editors insist that those errors be fixed before publication. Review is done voluntarily by scientists; this is part of the cost of being a member of this great human undertaking. Science doesn't claim Truth; although science strives to be as accurate as humanly possible, that is often well short of Truth. Asking grandpa what school was like in his childhood gives you a primary source (grandpa), even if he insists that he walked 20 miles through neck-deep snow, uphill both ways. Some primary sources have selective memories.
What sort of rock is pictured above?
Metamorphic; The rock separated into layers as it was cooked and squeezed deep in a mountain range. The large crystals, intergrown nature, and separate dark and light layers all point to metamorphism, deep inside a mountain range. Rapid cooling in volcanic eruptions gives tiny crystals, not the big, pretty ones here. You can see the former sand grains or other-sized pieces in sediment and sedimentary rocks. And marmot doo-doo consists of small, dark pellets, akin to big rabbit doots, and usually isn't considered to be rock.
Major differences between Mt. St. Helens and Hawaiian volcanoes include:
Mt. St. Helens is a medium-to-high-silica stratovolcano, and Hawaii has low-silica shield volcanoes. The low-silica lava from the Hawaiian hot spot flows easily, so the lava spreads out to make broad, gentle volcanoes that look like shields of medieval warriors. Melt a little basaltic sea floor with some water and sediment, and you get silica-rich andesite feeding explosive, subduction-zone stratovolcanoes such as Mt. St. Helens. Hot spots and spreading ridges make low-silica, basaltic volcanoes, which don't explode powerfully. Mt. St. Helens is a stratovolcano, but stratovolcanoes are steep, not broad and flat. Mt. St. Helens was the most active of the Cascades volcanoes even before its big 1980 eruption, and the volcano has erupted many times since the big eruption.
Human population continues to grow. Looking at many of the things we use on Earth (farmland and land for wood and other things, fish in the sea, etc.):
Our use is large but not everything; we are approaching use of half of all that is available We have removed perhaps 90% of the large fish in the ocean, and we raise crops or cut trees on much of the land surface. In very round numbers, we are approaching use of half of everything available on the planet, with the likelihood that we will greatly increase our population in the future.
What is accurate about seismic waves moving through the Earth?
P-waves (also called push-waves or sound waves) move through both solids and liquids. P-waves go through liquids and solids, because you can squeeze and release a liquid or a solid—push here and it squeezes a bit, which squeezes what is next to you... and on in a wave.
Which ocean is almost entirely encircled by volcanic arcs in a "Ring of Fire":
Pacific. The Andes, the mountains of central America, the Cascades, the Aleutians, Japan, New Zealand and others ring the Pacific in a subduction-zone ring of fire. The Pacific is getting smaller as it is gobbled up in these subduction zones. The Indian Ocean has volcanic arcs to the east, the Aleutians draw an explosive boundary to the Arctic Ocean between the mainland of Alaska and Siberia, there is a little Atlantic subduction-zone volcanism in the Caribbean and far south in the Scotian Arc, and that Scotian Arc contributes to a little subduction-zone volcanism around the "Southern Ocean" that encircles Antarctica, but none of the other oceans is encircled the way the Pacific is.
Geology departments are seeing a lot of recruiters recently, because geology is an in-demand major. Which of the following is NOT a job that geologists commonly end up doing?
Packaging substandard mortgages into "securities" and trying to sell them to unsuspecting people. Most jobs in geology involve finding valuable things: oil, clean water, ores, and more. But, geologists also teach and communicate in other interesting and entertaining ways, warn about hazards, and help understand the Earth system.
Volcanoes in Death Valley:
Produce rocks with similar composition to the rocks made at undersea spreading ridges, because Death Valley is geologically related to spreading ridges. Death Valley has spreading-ridge-type volcanoes, and if you go south from the Valley, you find the spreading ridge in the Gulf of California; Death Valley and the Gulf of California are geologically related. There have been recent eruptions in Death Valley (within the last centuries), but as of this writing, no volcanoes are currently erupting in Death Valley, nor have any erupted for over a century.
What tectonic setting is primarily responsible for producing Olympic National Park as well as the hills on which San Francisco is built?
Push-together subduction. The rocks of Olympic and San Francisco were scraped off the downgoing slab of the subduction zone
National Parks are:
Regions containing key biological, geological or cultural resources that have been set aside for the enjoyment of the present generation and future generations. Old Faithful, the giant sequoias, and Mesa Verde's cliff dwellings are waiting for you, and your grandchildren.
Hot spots:
Rise from as deep in the mantle as the core-mantle boundary to the surface of the Earth, bringing up heat and feeding volcanoes. Earthquakes make sound waves that go through the whole Earth, and go slower through hotter, less-dense rocks. By putting out listening devices called seismometers around the Earth, and listening to the waves from many earthquakes in many places, scientists can map the hotter regions, and find that towers of hot rock come up from way deep in the Earth in some places. But, some other hot spots don't seem to start as deep. The hot spots don't seem to move around much, but the lithospheric plates drift around over the hot spots. Hot spots come up beneath continents and oceans, and can poke through both. No one has ever found caffeine in a hot-spot plume, although it is possible that other things stir up trouble in Congress.
Geophysical evidence indicates that convection is occurring in the Earth's mantle. What is the most likely physical explanation for why convection can occur in the mantle?
Rocks deep in the Earth expand and so become lower in density and tend to rise as they are heated, and the deep rocks are warm enough to flow slowly even though they are mostly solid. Convection seems so easy, but describing it in words is not. For "ordinary" convection, one needs something capable of flowing (gas, liquid, or soft solid), heat below and cold above with expansion reducing density on heating and contraction increasing density on cooling, and then a bit of time and a perturbation of some sort to get the motion started. If you had something that expanded on cooling and contracted on heating, and you had cooling below and warming above, you could also make convection work. The mantle is mostly solid, the outer core can't directly stir the mantle or cause convection, and the magnetic field doesn't do much to move rocks.
You drill through the muds at the bottom of the sea floor and sample the rocks beneath, and you then determine the ages of those rocks, using standard scientific techniques. As described in the course materials, you will find that:
Rocks farthest from spreading ridges are oldest, with ages decreasing as you move toward a ridge. At sea-floor spreading ridges, hot magma rises up, cools and solidifies. These rocks then split and move apart as yet more magma rises, cools and solidifies. Over time, the rocks are moved great distances (tens or hundreds of miles) from the spreading ridges. The rocks close to the ridges were deposited recently (they are "young"), but the rocks far from the ridge were deposited long ago and then moved away slowly (they are "old").
Opinion polls show most residents of the US do not believe they understand science very well, but they do favor more government support of science. Why do most US residents favor government support of science?
Science has helped make our lives healthier, wealthier, easier, safer, etc., and people hope that more funding of more science will provide even more health, wealth, ease, safety, etc. Without science and technology, the great majority of us would be dead, so we tend to be supporters of science. Although we know that science works, we're never sure that it is completely right. Students so often discover things that professors missed, or that professors got wrong, that scientists would be silly to claim Truth. Comparing the TV ratings of the latest hit to the ratings of the latest science program on public broadcasting shows that many Americans are not fascinated by science, but the science-show ratings are above zero, so some people are fascinated by science. And hope as we might, it is unfortunately clear that not every scientist is sexy (just most of them are...).
Opinion polls show most residents of the US do not believe they understand science very well, but they do favor more government support of science. Why do most US residents favor government support of science?
Science has helped make our lives healthier, wealthier, easier, safer, etc., and people hope that more funding of more science will provide even more health, wealth, ease, safety, etc. Without science and technology, the great majority of us would be dead, so we tend to be supporters of science. Although we know that science works, we're never sure that it is completely right. Students so often discover things that professors missed, or that professors got wrong, that scientists would be silly to claim Truth. Comparing the TV ratings of the latest hit to the ratings of the latest science program on public broadcasting shows that many Americans are not fascinated by science, but the science-show ratings are above zero, so some people are fascinated by science. And hope as we might, it is, unfortunately, clear that not every scientist is sexy (just most of them are).
Which of the following is not expected very often near a "textbook" subduction zone (that is, near a subduction zone that is so perfect and free of confusing complications that you would use it in a textbook to teach students)?
Slide-past (or transform, with horizontal but no vertical movement) earthquakes and faults such as the San Andreas. Most of the action at subduction zones is "push-together", including push-together earthquakes and faults, scraping off of sediment to make piles as one side moves under the other side, and volcanic explosions that contribute to layered volcanoes, or "stratovolcanoes". Slide-past motion is not dominant, intermediates between pure subduction and pure slide-past motion do exist, but are not "textbook" cases of subduction.
In the picture above, the pink and yellow arrows in front of Dr. Alley point to two rather different deposits from an eruption of the Hawaiian Volcano Kilauea. As described in the class materials, these materials are:
Small pieces thrown through the air, and frozen "waterfalls" of lava that flowed quietly before freezing. Mt. St. Helens and similar volcanoes make giant explosive eruptions that throw bus-sized blocks, but Kilauea in Hawaii usually doesn't (although rarely, water flashing to steam may move some big things!). Dr. Alley showed you the gravel-sized pieces of glass at the end of the pink arrow, and the frozen "waterfall" of lava at the end of the yellow arrow.
Geologists get to play with chemistry, physics, biology... and history! And what a history you will meet as you work your way through the course. Starting at the beginning, the textbook provides the scientifically accepted start of the story... and promises that you'll get to explore some of the evidence for that scientific view, later in the semester. Meanwhile, which is more nearly correct of the scientifically accepted view?
The Earth formed from the falling together of older materials, about 4.6 billion years ago. The Big Bang is estimated as having occurred about 14 billion years ago. Stars that eventually formed in the wake of the Big Bang led to production of elements such as iron and silicon that are common in the Earth—we are formed from second-generation stardust, which "got it together" to make the planet about 4.6 billion years ago.
What is more accurate about the Earth?
The Earth is formed of concentric layers (something like an onion--a central ball with a shell around it, and a shell around that...); when the planet melted, it separated into layers. The planet is onion-like, with an inner core, then an outer core, a mantle (which has several sub-layers), and a crust. The moon-making collision did happen, but the planet got hot enough to separate again. The planet separated after melting largely or completely, with the densest stuff falling to the center and the lowest-density stuff floating to the top.
The Earth is layered. Most geologists believe that this layering originated primarily because:
The Earth partially or completely melted soon after it formed, and the denser materials fell to the center. Melting allows things to sort out more easily. Think of the rocks and snow and ice and salt and squirrel parts that stick on the bottom of your car when you drive in a snowstorm, and how they sort themselves out when they melt in the garage or in the spring. Much evidence points to early separation of the Earth into layers, before the collision with a Mars-sized body that blasted out the material that made the moon, although a little bit of separating may still be going on. The type of material falling together to make the planet may have changed as the planet formed, but this doesn't seem to have been too important in controlling things. And mighty as the Supreme Court may be, this was a bit before their time.
Most of the material moved by volcanoes is from the few, big ones rather then from the many, little ones. Most of the material moved downhill in landslides is in the many, little ones rather than the few, big ones. In comparing the importance of the few, big earthquakes to the many, little earthquakes, are earthquakes more like volcanoes (the few big ones matter most) or like landslides (the many little ones matter most)?
The few, big earthquakes matter most (like volcanoes). An increase of 1 in earthquake magnitude increases ground shaking about 10-fold, increases energy release about 30-fold, and decreases frequency about 10-fold; the 30-fold increase in energy more than offsets the 10-fold decrease in frequency of occurrence. We wish earthquakes did no damage, but the millions of people who have been killed in earthquakes over the centuries would, if they could, testify to the damage done by earthquakes. And historical records of earthquakes clearly preceded the Simpsons.
On the Richter scale of earthquake intensity
The ground is shaken 10 times more by a magnitude-6 quake than by a magnitude-5 quake One problem in describing earthquakes is that the ground shaking in the smallest one you can feel is 1,000,000,000 times smaller than the ground shaking in the largest quakes. We usually dislike having a scale that requires us to talk about an event of, say, size 100,000,000; instead, if a magnitude-1 quake moves the ground 10 units (say, 10 nanometers at some specified distance from the quake), than we say that a magnitude-2 quake moves the ground 100 units, and a magnitude-3 quake moves the ground 1000 units, and so on. You'll notice that the magnitude is just the number of zeros after the 1; this is a logarithmic scale.
In the picture above, Dave Janesko holds two rocks next to each other. The black one (to the upper left in the picture) is from a lava flow, and is much younger than the red one (to the lower right in the picture), which is a lake sediment. In nature, these rocks are found the way Dave is showing, with the younger black one next to the older red one rather than being on top of the older red one. As described by Dave Janesko in the online video, what happened here?
The lake sediments were deposited, then the lava flowed on top, and then a pull-apart Death-Valley-type fault formed, breaking the rocks and dropping the lava flow to be next to the lake sediments. The spreading that opened Death Valley affected a lot of the west, all the way over to Bryce Canyon in Utah. The Sevier Fault, just west of Bryce, formed as pull-apart action broke the rocks, allowing younger rocks including the black lava flow to drop down next to older rocks including the red lake sediments. There really are cases where lava hardens in cracks, or where lava flows fill valleys, but a careful examination of the rocks here shows that the lake sediments have not been heated by nearby lava, so these lake sediments and the lava must have been placed together after the lava cooled. Folding does occur, but not here.
Which is accurate about the Earth?
The lithosphere usually breaks rather than flows, and the asthenosphere usually flows rather than breaks. Litho means stone, and the lithosphere is the hard breakable layer, above the softer asthenosphere.
Earthquakes can be caused in many different ways. The best interpretation of the planet's earthquakes is that:
The rare, deepest ones are caused by "implosion" as minerals in downgoing slabs of subduction zones suddenly switch to a denser arrangement, whereas common shallower ones are caused by elastic rebound of bent rocks when a fault breaks. "Implosion" is the currently favored idea. As subduction zones take rocks deeper where pressure is higher, the building blocks tend to reorganize to take up less space, shifting from, say, a one-on-top-of-another pattern to a fit-in-the-space-between-those-below pattern. Sometimes, this seems to be delayed and then to happen all at once (I can't move until my neighbor does...), giving an implosion. The biggest, deepest earthquakes happen where temperatures and pressures are so high that we don't think rocks can break. Humans have never made a hole anywhere nearly as deep as the deeper earthquakes. We have mostly quit testing atomic bombs. And, coffee shops just aren't buried deeply enough to account for the deepest earthquakes.
What is an accurate description of the job of a scientist?
The scientist invents new ideas, and goes on to show that some of those ideas are false. Much of the fun in science is coming up with great new ideas (hypotheses, if you like fancy words). But for your new idea to "win", you have to show that it does better than old ideas, so you have to prove those old ideas false (or incomplete, or not-quite-right, or whatever "nice" word you might prefer). The scientific method is a powerful way for humans to learn to do things, and learn what does and doesn't work, but the results of science are always open to improvement, so are not claimed to be Truth, and probably are not Truth. Some scientists still use pencils and look at things, and there are probably a few non-sexy scientists around somewhere.
You use highly accurate techniques to learn the time when lots and lots of different volcanic rocks solidified from melted rock. You do this for many different rocks across the continents, and many different rocks across the sea floor. You will find that (note that "older" rocks are those that solidified more years ago, and "younger" rocks are those that solidified fewer years ago.):
The sea-floor rocks are typically younger than the continental rocks, because sea-floor rocks are taken back into the mantle at subduction zones about as rapidly as new sea-floor rocks are produced, while continental rocks are not taken back into the mantle at subduction zones. You can find young rocks on the sea floor and on the continents, but all of the old rocks on the planet are on continents—there are no old sea-floor rocks. The older sea floor has all been recycled at subduction zones.
Chemical reactions involve:
The sharing or trading of electrons. The clouds of electrons around the nuclei of atoms serve as the Velcro of the universe. Atoms gain or lose electrons and then stick together by static electricity, or else share electrons and stick together inside the shared cloud. The nuclei with their protons and neutrons (which are themselves composed of quarks, which also were called partons at one time) are the things held together by the electronic Velcro of chemistry.
You find two neutral atoms. Each has 8 protons in its nucleus, but one has 7 neutrons, and the other has 8 neutrons. It is correct to state that:
The two atoms are from the same element, but are different isotopes of that element. The element is determined by the number of protons, so if each atom has the same number of protons, the atoms are the same element. Changing the number of neutrons primarily affects the weight, giving a different isotope of the same element. (Changing the number of neutrons too much can introduce radioactivity, so the isotope won't hang around forever.) Ions are made by gaining or losing electrons. Isopleths are lines on a map connecting places with the same concentration of something that someone has measured, not exactly relevant here. And cola requires making atoms into molecules, and then mixing molecules of several sorts (water, sweetener, coloring agent, flavoring agent, perhaps caffeine) to make cola.
The picture above shows river gravels in the bottom of Death Valley. Based on the lesson materials for this unit, a likely explanation for this occurrence of river gravels in the valley bottom is:
The valley was dropped relative to the mountains by faulting, and rivers now are carrying gravels down from the mountains into the valley. Faulting dropped the valley (or raised the mountains, or more likely both), and the melting snows of the mountains feed rivers that carry rocks down into the valley, slowly filling it up while lowering the mountains. There really are deep canyons that were carved by rivers, but as we saw in class and online, Death Valley is not one of them. Rivers dont run on the tops of mountains to deposit gravels. And Daisy was more into shorts than into long jumps.
The age of rocks near a sea-floor spreading ridge can accurately be described as:
The youngest rocks are near the ridge, and the rocks get progressively older as you go away from the ridge in both directions. At sea-floor spreading ridges, hot magma rises up, cools and solidifies. These rocks then split and move apart as yet more magma rises, cools and solidifies. Over time, the rocks are moved great distances (tens or hundreds of miles) from the spreading ridges. The rocks close to the ridges were deposited recently (they are "young"), but the rocks far from the ridge were deposited long ago and then moved away slowly (they are "old").
The photograph above shows some rocks in Great Smoky Mountains National Park. From looking at the rocks, and what you know about the park, a likely story is that:
These rocks were buried deeply and squeezed in a continent-continent collision, and then brought to the surface as overlying rocks were eroded. The squeezing and heating of an obduction zone have changed these rocks from mud to the folded schist seen here, and then erosion has revealed the rocks at the surface. There were large volcanoes near where the Smokies are before the Smokies formed, but those volcanoes ended when subduction ceased and obduction started to build the Smokies. Some slide-past motion did occur in the Appalachians, but not a huge amount, and the Smokies were not brought up from Florida.
Old, cold ocean floor sinks at subduction zones. Why does this cause melting to feed volcanoes?
Water taken down subduction zones lowers the melting temperature in and near the slabs Throw a little dry flour in a warm oven, and not much happens. Add some water, or better, some water and some carbon dioxide from yeast, and things happen in a hurry. The subduction zone takes water, and carbon dioxide in shells and other things, down to lower the melting point and feed volcanoes. Friction does warm the down-going slabs, but slabs start off way colder than the rocks into which they move, and remain colder for a while. Sliding your cold feet along the sheets when you get into bed on a winter night may warm your toes a little by friction, but if you happen to share the bed with a significant other, putting your tootsies on that persons bare belly will tell you that frictional heating takes a while! The scraped-off pile of sediment traps a tiny bit of heat, but not too much; the downgoing slab makes the nearby mantle colder than normal, not warmer. And nature tends to separate regions where something is flowing one way from regions where the flow is reversed; if the flows are too close together, one will drag the other along and change its direction. Hot spots occasionally ride along on spreading ridges, because both involve rising, but not on subduction zones.
The great scientist Alfred Wegener proposed that continents have moved, while other scientists such as T.C. Chamberlin argued against Wegener. Wegener's ideas eventually won, and are now widely accepted, because:
Wegener's ideas did a better job of predicting the results of new observations and experiments. Unlike painting or literature, scientific inquiry has a well-defined procedure for figuring out if Wegener's ideas are better or if Chamberlin had it right all along. In looking at a painting, we can ask different people what they think, or we can make up our own mind on whether we like it or not, and that is perfectly valid. In science, we have to ask: does the idea fit with the way the world works? Can I predict the results of the next observation better using Wegener's ideas or Chamberlin's? As it turns out, Chamberlin's ideas didn't predict things very well, and Wegener's did.
Using ordinary means (fire, sunlight, our digestive systems) we can take matter apart into smaller and smaller pieces, and the smallest pieces we typically produce are:
atoms
The cartoon above illustrates a specific geologic process. Which of the additional geologic images DOES NOT feature this same process at work?
mountain with white snow on top The folded Appalachians, including the region of central Pennsylvania around Penn State's University Park campus, shown in the satellite image here, as well as the Great Smokies and the Blue Ridge, formed when Africa and Europe collided with the Americas, much as the two cars in the picture collided. Death Valley records different processes.
The processes that made Death Valley have been operating for millions of years, and continue to operate today. For this question, ignore the sand and gravel moved by water and wind, and think about the big motions of the rocks beneath. If you had visited Death Valley 1 million years ago, you would have found the valley then to have been (choose the best answer):
narrower and shallower than it is today The pull-apart action that is spreading Death Valley and surroundings also involves uplift of mountains or downdrop of valleys, and Death Valley has dropped as its flanking mountains have moved apart. Thus, in the past the valley was narrower and shallower than it is now, and the motions have deepened and widened the valley.
