Geo Practice Quizzes

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." Feedback: 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.

You put some atoms together, and they share or trade some electrons. What just happened was:

A chemical reaction. Feedback: 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.

Look at the picture above. What happened here?

A great volcanic explosion occurred, spreading material across the landscape and leaving a hole. FB: 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. And while George is cute, he could never dig such a hole. This is the aftermath of the eruption of Mt. St. Helens.

Look at the picture above. What type of volcano is this?

A hot-spot-type, basaltic shield volcano FB: This is Mauna Loa, on the island of Hawaii. It is a broad, gentle shield volcano, not very similar to the steep stratovolcanoes of the Cascades. Plateau basalts cover state-sized areas with very flat-lying flows, cinder-cone volcanoes are much smaller and steeper, and George's piles are smaller yet.

The pictures show evidence of where mud has moved, or hasn't moved. The pictures also tell you something about when mud moves—Dr. Alley took the pictures when it wasn't raining, and while he was taking them he did not get his bike tires buried by mud. A reasonable interpretation is:

A lot of downhill motion of material occurs over relatively short times (when it's raining), and some places contribute much more material than others. FB: Trees and grass slow the downhill creeping of dirt, and really slow the downhill washing of dirt. A very small bare spot may supply more mud in a rainstorm than a big grassy area—construction sites do make nearby streams muddy during rainy times unless care is taken to trap the mud. Most of the mud moves in short intervals, especially during really heavy rains.

Scientists often speak of consensus—the scientific community agrees that a particular theory is better than the competitors. What is such scientific consensus based on?

A number of different experiments by different people that all had outcomes that were predicted accurately by the favored theory and not by the competitors.

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. Feedback: 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?

Humans (and our crops and pets and farm animals) now use:

Almost half of the things the planet makes available and that we like to use. Feedback: 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.

Death Valley National Park preserves the lowest-elevation, hottest piece of the U.S. The park is fascinating for many reasons. What is accurate about volcanoes and Death Valley National Park?

Although no volcanoes are actively erupting at the moment this is being typed, eruptions have occurred in the geologically recent past (the most recent centuries or millennia), demonstrating the presence of hot rock at shallow depth beneath the valley. FB: Death Valley, and many of the surrounding parts of Nevada and California, have experienced geologically recent volcanic activity. This is one of the problems facing the plan to put nuclear waste in an underground repository in Nevada and leave that waste—are we sure that a volcano won't erupt through the repository? There has not been enough lava erupted to fill the valley, however, nor do volcanoes erupt Diet Pepsi (although you can make a nice volcano model by quickly popping the top of a hot, shaken can of pop).

Chemists recognize many different elements, such as gold, or oxygen, or carbon, or iron. Suppose you got some iron, and started splitting it into smaller pieces. The smallest piece that would still be called "iron" would be:

An atom Feedback: 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 they wouldn't be gold any more; you can make any of the elements out of these pieces.

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. FB: 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.

Which of the following is commonly expected 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)?

Andesitic stratovolcanoes, such as Mt. St. Helens, fed by melt from the slab being subducted. FB: Pull-apart earthquakes and faults often occur at pull-apart basaltic mid-ocean ridges, which are not subduction zones. Slide-past also occurs on the planet, but not primarily at subduction zones, which also are not hot spots. But subduction does lead to layered thick-lava-flow/blown-up-bits stratovolcanoes of andesitic composition.

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. FB: 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.

Look back at pictures 2 and 1. These are close to each other. 1 is fairly new paving on a road, and 2 is a somewhat older bicycle trail. An hypothesis that is reasonably motivated by these observations, and by the other blacktop pictures from the previous question, is:

Bicyclists aren't as heavy as cars, and the extra stress from heavier things tends to crack blacktop. FB: You can break a brand new coffee mug by hitting it with a hammer. Damage tends to accumulate with time, but extra stress also causes damage to accumulate. The bicycle trail is not stressed as much as the road because bicycles are lighter than cars and trucks, so the blacktop on the bicycle trail can last longer than the blacktop on the road.

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?

C is slide-past, B is pull-apart, and A is push-together. FB: 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).

Which is not part of our modern view of geology?

Convection in the Earth primarily occurs in the lithosphere, and not in the deeper rocks. FB: Convection occurs in the hot, soft rocks beneath the lithosphere, not in the relatively stiff, rigid lithosphere.

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. FB: 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.

Compare pictures 1, 3, and 5. All are blacktop roads, in a similar place, that experienced similar traffic (except that after it fell apart, 5 is no longer used much), but 1 has not been around very long, 3 in-between, and 5 for a long time. A reasonable inference is:

Damage accumulates with time so that older blacktop is more broken up. FB: The recently laid blacktop looks pretty good, and the blacktop that was put down the longest time ago is barely recognizable as blacktop. You should not be surprised to learn that damage tends to accumulate with time as the blacktop breaks up.

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. FB: 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.

There are numerous clues in these pictures to how rapidly loose material can roll, slide, or otherwise move downhill, and the conditions needed for such motion. Some interesting things you can learn include:

Downhill motions can be slow (years or decades or longer) or fast (days or less). FB: Most soil motion is fairly slow, maybe an inch a year or so, and grass or trees tend to hold the soil and slow the motion. But, sometimes a giant landslide sweeps things away in seconds, or a groundhog moves more dirt in an afternoon than the slow creep would have moved in a year. Really understanding how the surface changes requires thinking about many processes operating at many speeds.

Some eruptions come out of volcanoes really rapidly and shoot really high because:

Dropping pressure as the melt rises allows volatiles including water vapor and carbon dioxide to make bubbles that lower the density and make the melt rise even faster. FB: Just as uncapping a shaken soda bottle or champagne bottle allows a foaming "eruption", it is the bubbles forming in rising lava that make it go fast. Although stomping on a fast-food ketchup package can cause a squeeze-driven "eruption", real volcanoes are not primarily squeeze-driven, mostly because it takes a pretty big "stomp" to drive one, and the Earth doesn't stomp hard enough (even in earthquakes!). (The squeezes that fold and break rocks to make mountains are actually rather slow.) Hot-spot volcanoes tend to erupt quietly, slowly, and not very high into the air. Spreading ridges don't pull on their surroundings; the ridges actually push a little. And George surely can't do that, even if he is cute.

Now consider the following statement: "At least we don't need to worry about weather and landslides and downhill motion and all of those things attacking buildings, because natural processes don't bother buildings.

False FB: Nature attacks buildings, just as nature attacks pavement. Some of your rent (if you rent), and some of your tuition (if you pay it), are used to patch buildings, but the wear shows anyway.

A scientist sees a crack near a tree. A scientist, doing real science, will assume that the tree caused the crack, call it science, and move on.

False FB: Science is really people trying to understand the world by working really hard, following their curiosity, but agreeing to follow a set of rules that make it very hard for them to fool themselves and others. The idea that the tree roots crack the sidewalk is a starting point for science, not an ending point.

Hot spots usually:

Feed basaltic volcanoes (composition similar to sea floor). FB: 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. Feedback: 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.

Continents

Have grown in area over time primarily by addition of island arcs, seamounts and sediments scraped off subducting slabs. FB: Observations show that the continents have grown, as pieces were added to the continent sides; the centers of continents are very old, and then younger rocks occur in belts around the old cores. If you kept loading the conveyor-belt at the grocery store, but there were no baggers and you refused to bag your own, you'd end up with a giant clot of groceries mashed together at the end. That is not a bad model for how continents form. If a watermelon runs into a loaf of bread, you get a big mountain-building event! Hot spots poke through continents occasionally, but don't cause much spreading so don't cause much continental growth. "Suspect terrane" is an old geologic term for rocks that drifted in on a subducting slab and then mashed up onto a continent. Geologists long "suspect"ed that these "terranes" were weird, and eventually figured out the explanation, but named them before learning the explanation. Continents can be stretched and thinned at spreading centers, and some of those spreading centers do fail and leave a stretched continent that hasn't broken to make an ocean, but more commonly the stretching continues until an ocean is made.

Which statement is true about the physical conditions required for convection to occur?

Heating from below, which reduces density and causes a tendency for the heated material to rise. FB: 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.

Icebergs float in water and continents float above the mantle because:

Icebergs/continents are less-dense than the stuff they float in. FB: Flotation and buoyancy are driven by density differences. In general, less-dense objects float higher up than more-dense objects would. Sometimes the density differences are due to temperature, sometimes due to composition. In the case of icebergs, water is denser than ice, so ice floats. Similarly continental crust is less dense than the mantle.

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. FB: 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.

It would be really nice to know whether an earthquake is coming, so we could prepare for it. At this time, we are able to:

Make reasonably accurate estimates of where earthquake damage is likely, and how bad earthquake damage is likely to be, but not exactly when an earthquake will occur. FB: 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. It is possible (but unproven!) that animals do act strangely before a quake, and it is known that water levels in wells may change as the ground begins to break and fail before some quakes, but water levels in wells can change for lots of reasons, and animals act strangely for lots of reasons. But knowing where quakes are likely is useful; it is wise to build things to withstand the events that are likely to occur, but not to spend too much money preparing for events that are highly unlikely over the life of the building. And in central Pennsylvania, the "great" Centre Hall earthquake of a few years ago was felt across much of the region, although it caused no notable damage.

Bigger earthquakes occur less frequently, but a bigger quake releases more energy and does more damage. An interesting question to ask about earthquakes (and about almost anything else!) is whether the increase in energy release and damage done is larger or smaller than the decrease in frequency as one looks at bigger earthquakes. Asked a different way, is most of the damage done by the many little earthquakes or by the few big earthquakes?

Most of the damage is done by the few, big earthquakes. FB: An increase of 1 in 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 earthquakes are actually very poor at distinguishing the brands of soda dispensed by or advertised on machines.

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. FB: 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.

Newton's ideas on physics "won", and Aristotle's ideas were kicked out of science and over into history. Why?

Newton's ideas did a better job of predicting how nature would behave. Feedback: Unlike painting or literature, scientific inquiry has a well-defined procedure for figuring out if Newton's ideas are better or if Aristotle 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 speed of a falling object better using Newton's ideas or Aristotle's? As it turns out, Aristotle's ideas didn't predict things very well, and Newton's did.

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. Feedback: 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.

The pictures and their descriptions give you many insights to the processes by which the environment acts on rocks. These processes likely include:

Physical and chemical alteration, including many chemical processes such as rusting and dissolving in rainwater and beneath lichens. FB: A gravestone doesn't need to stand up to one physical or chemical process, but many physical and chemical processes. Chemically, rain is naturally slightly acidic, our coal-fired power plants increase the acidity, lichens make their own acids, and acid attacks rock, while oxygen and water rust the iron in some minerals, and much more. In the words of Dr. Suess, "There I was all completely surrounded by trouble..."

Based on what you know about the world, and what you can see in the pictures, the most likely explanation why corners lose more chips than faces is:

Pieces on corners can be hit from two sides, while the middle of a face can be hit from only one side; and, a piece on a corner isn't supported by as many neighbors as a piece on a face. FB: Neighbors are useful in lots of ways. They can protect you from sneak attacks coming from behind or beside you, and hold you up in case you start to fall. Lose the guard and the support, and you're more vulnerable. The same is true for erosion—something sticking out on a corner is more likely to get hit and less strongly held in place, and so is much more likely to break off.

What tectonic setting is primarily responsible for producing Mt. St Helens?

Push-together Subduction FB: Mt. St. Helens sits above a subduction zone, where one tectonic plate goes below another as they come together.

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. Feedback: 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. FB: 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.

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. FB: 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").

What is accurate about seismic waves moving through the Earth?

S-waves (also called shear-waves) move through solids but not liquids. FB: S-waves are a bit like waves on a rope—grab an end and move it sideways, which moves the neighboring part sideways... This works with solids, but not liquids, which cannot "grab" and move the neighboring part.

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. Feedback: 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.

What tectonic setting is primarily responsible for producing the great San Francisco earthquake and the San Andreas Fault?

Slide Past Not much mountain-building is happening along the central coast of California; the rocks slide past horizontally. The sliver of California to the west of a line connecting San Francisco to Los Angeles is sliding to the northwest, and as the sliver slides, it sticks and slips, making earthquakes.

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. FB: 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.

The Earth has a fascinating history, which this class has just begun to explore. Which is more nearly correct, according to the scientific interpretation presented in the text?

The Earth formed about 4.6 billion years ago, well after the Big Bang, as materials made in stars fell together to form the planet.

The scientific study of the origin of the planet has taken a lot of effort, and still generates much discord outside the scientific community although almost no discord within the scientific community. The scientifically accepted history is:

The Earth formed from older materials that fell together under gravity about 4.6 billion years ago. Feedback: 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. Feedback:

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. Feedback: Melting allows things to sort out more easily. Think of the rocks and snow and ice and salt 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.

There is a deep trench in the sea floor off the Marianas volcanic arc of explosive, andesitic, Ring of Fire volcanoes in the South Pacific, but the water is not deep off the coast of Oregon and Washington near Mt. St. Helens and the Olympic, because:

The Marianas, Oregon and Washington have had the sea floor bent downward by subduction to make trenches, the trench off Oregon and Washington is filled by sediment eroded from the nearby continent, but the Marianas don't have a nearby continent and so the trench there is not filled with sediment. FB: The more rocks there are nearby, the easier it is for erosion to move some of those rocks. The trench off Oregon and Washington has Oregon and Washington nearby, with lots of rocks. Add in that Oregon and Washington have great rivers such as the Columbia, and huge glaciers that grind up the rocks such as the beautiful glaciers on Mt. Rainier, and there is lots of sediment to fill the trench and be scraped off the subduction zone to make Olympic National Park. The Marianas involve subduction of older, colder sea floor under younger, warmer sea floor, have less rock above sea level nearby to be eroded, are in a warm place without glaciers, and so haven't filled the nearby trench with sediment. There probably are a few discarded floppy disks, as well as a lot of other human-produced material, in the trench off Oregon and Washington, but nature has been a lot more important than humans in filling the trenches. Humans did once talk about disposing of radioactive waste in the trenches, but then we found out that whatever goes down the trench comes back up, and may be squeezed and broken and squirted back up quickly, so we gave up on that idea. And the volcanoes of Oregon and Washington are subduction-zone volcanoes, not hot-spot volcanoes.

What is the "Ring of Fire"?

The complex of volcanic arcs fed by subduction zones encircling the Pacific Ocean. FB: The "Ring of Fire" is the circle of volcanic arcs fed by subduction zones with scraped-off muds and deep earthquakes around the Pacific Ocean.

Based on the appearance of the numbers and the corresponding text in the first six pictures, it is most likely that likely that:

The different stones wear away at different rates, with granite most resistant and marble least resistant. FB: Time and stress matter, but so does composition. People behave differently at different ages in their lives, and may change behavior as the stress level changes, but what you're really made of does show through in the tough spots. For rocks, granite stands up to the weather better than marble does in a Pennsylvania graveyard.

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. FB: 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.

Which is accurate about the Earth?

The lithosphere normally breaks, and the asthenosphere normally flows. FB: Litho means stone, and the lithosphere is the hard breakable layer, above the softer asthenosphere.

In chemistry, the type of an atom (what element it is) is determined by:

The number of protons it contains in its nucleus. Feedback: Physicists change the name when the number of charged, massive protons in the nucleus changes. Adding one proton makes a HUGE difference to how an atom behaves, and so deserves a new name. The neutrons hang around in the nucleus to keep the protons from kicking each other out. Exchanging electrons is important, but doesn't change the element type.

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. FB: "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. Feedback: 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.

Dave has just informed everyone that the black rocks, which formed by cooling of a very hot lava flow, are much younger than the red rocks, which formed from sediments deposited in a lake. He has examined the red rocks and found that they have not been "cooked" by heat from the black rocks, so the red and black rocks must have been placed together after the black rocks cooled. And, he has examined the contact between red and black rocks and found that it is a fault that has been scratched by the motion of the rocks along the fault. It is likely that:

The scratches are nearly vertical, because the black rocks were dropped down along a pull-apart fault to lie next to the red rock. FB: 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. The scratches are not too far from vertical, made as the rocks dropped down.

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. FB: 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.

20-mule teams hauled borax salts out of Death Valley, and the valley still has lots of salt, sand, and river gravel in the bottom. The most likely explanation is:

The valley was dropped relative to the mountains by faulting, and rivers have been (and still are) carrying gravel, sand and salts down from the mountains into the valley; then the water evaporates and leaves the gravel, sand and salts behind.

Based on what these pictures show, and the text accompanying them (note: erosion refers to the removal of rock material from the stones):

There may be several mechanisms of erosion, including chemical action under lichens, breaking off of chunks, and bit-by-bit removal that isn't occurring under lichens. FB: A gravestone is "attacked" in many ways—bumped by lawnmowers, cracked as ice grows in tiny cracks on a cold night, and attacked chemically.

One of the big problems faced by National Parks is that:

They must allow people to enjoy things today, and preserve those things for the future, but achieving both of these is not easy. Feedback: 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! Fortunately, caffeinated chipmunks are not big problems.

Much melting in the mantle occurs near subducting slabs primarily because:

Water taken down subduction zones lowers the melting temperature in and near the slabs. FB: 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 cartoon above illustrates a specific geologic process. Which of the additional geologic images DOES NOT feature this same process at work?

snowy mountain top (cars pushing)