GEOSCI ROCK ON's

What is one of the main, common-sense ideas that geologists use to learn what happened first and what happened later in geologic history?

If you see a push-together fault cutting a clastic sedimentary rock, you know that the sediment was deposited, and then broken by squeezing, because something must exist before you can break it.

The Precambrian:

Is the age of algae, and occurred just before the Paleozoic.

You start with 400 parent atoms of a particular radioactive type, which decays in a single step to give a stable offspring, and you start with none of those stable offspring. You wait just long enough for two half lives to pass. You should expect to have how many offspring atoms (on average)(remember that the number of parents and the number of offspring add up to 400, so if you have 10 parents, you have 390 offspring because 10 and 390 add up to 400, and if you have 20 parents you have 380 offspring, and so on):

300.

Acadia National Park has a long, rich and varied geologic history. The large island marked "I" in the middle of the above picture is composed of resistant granite from the long-ago closure of the proto-Atlantic. However, the shape of the island was formed by much more geologically recent processes (within the last 100,000 years or so). What is primarily responsible for the beautiful shape of the island?

A glacier flowed over the island, moving from left to right, smoothing the rocks encountered first and plucking rocks free from the other side.

The picture above shows an outcrop along Interstate 70 in Utah. The green arrow points to a person, for scale. Between the pink arrows there is an interesting surface. What is it?

An unconformity, where erosion occurred before the rocks above were deposited.

What is indicated by the yellow lines in the image above, which separate flat-lying sedimentary rocks, on top, from slanting sedimentary rocks beneath? Correct!

A great unconformity, with sedimentary rocks above resting on older sedimentary rocks below.

What can you learn about past environments from sediments and sedimentary rocks?

A huge amount, including whether the environment was land or water, whether it was warm enough for crocodiles or cold enough for ice, and much more.

The pink arrows point to a barrier beach, formed when waves fromthe ocean (on the left) washed away mud and piled up sand, after themud and sand were delivered by the stream flowing in from the upperright. The yellow arrows point to interesting features. How did they form?

A storm broke through the barrier beach and pushed sand farther inland.

Look at the picture above which shows a region just less than a foot across, of a stream deposit from the base of the same pile of rocks that show up in Bryce Canyon. This picture was taken in the face of a cliff in Red Canyon, just west of Bryce Canyon National Park. A indicates a piece of limestone that has been rounded off in a stream; Bindicates a mass of sand glued together by hard-water deposits, and C indicates another such mass of sand glued together by hard-water deposits . In order of time of formation, they are:

A was formed first, then B was glued together by hard-water deposits, then C was glued together by hard-water deposits.

There are many greenhouse gases, including carbon dioxide (CO2), methane (CH4). and vaporized water (H2O). These and other greenhouse gases warm the Earth primarily by:

Absorbing some of the infrared radiation emitted from the Earth.

Dr. Alley is pointing to a brownish zone exposed in the low bluff along Coast Guard Beach, Cape Cod National Seashore. The brown zone is rounded on the bottom, flat on the top, rests on sand and gravel, and has sand dunes on top. In the lower picture, Dr. Alley is showing that the brown zone contains twigs and other organic material. What is the brown zone doing here?

An ice block from the glacier was buried in sand and gravel, then melted to make a lake that filled with organic material.

Look at the picture above, which shows a small section of a "fossil" sand dune (a sand dune in which the grains have been "glued" together by hard-water deposits). When the dune was first deposited, which was down (which letter is closest to the arrow that is pointing in the direction you would have looked to see the ground when the dune was deposited)?

B (---->B)

You are flying along the coast, and you observe a sort of dam or wall, called a groin, sticking out from the coast. Sediment has piled up on one side of the groin, with erosion on the other side. You can reasonably infer that:

Before the groin was built, sediment transport in the longshore drift was dominantly from the side with the sediment deposit to the side with the erosion, and the groin has interrupted some of this transport.

If you were looking for different types of coal, you likely would find:

Bituminous in the sedimentary rocks of western Pennsylvania, and anthracite in the metamorphic rocks of eastern Pennsylvania.

Some natural resources are renewable—nature produces them fast enough that humans can obtain valuable and useful supplies of a resource without depleting it. Other natural resources are nonrenewable—if we use the resource at a rate fast enough to matter to our economy, the resource will run out because use is much faster than natural production. What do we know about oil and coal?

Both oil and coal are nonrenewable resources, and at current usage rates and prices similar to today, oil will run out in about a century and coal will run out in a few centuries.

What do we know about the effects of humans on extinction of plant and animal species on Earth?

Both prehistoric and modern humans have been responsible for extinctions.

You are the chief biodiversity officer for the National Park Service in the eastern US, responsible for maintaining as much diversity as possible, and your boss has told you to focus on maintaining biodiversity of things big enough to see with the naked eye (so you don't need to worry about microorganisms). You have two parks, and enough money to buy 10,000 acres of land. You may add the 10,000 acres to one of the parks, add 5,000 acres to each park while leaving them as isolated parks, or buy a 10,000-acre corridor connecting the two parks. All of the land for sale is now wilderness, but the land you do not buy is going to be paved for a super-mega-mall. You would be wise to:

Buy the corridor connecting the two parks; this keeps one big "island" rather than two smaller ones, and so keeps more species.

Which is the correct age progression, from older (first) to younger (last)?

C, D, E, F, B The package of sediments C, D, E, F is upside-down, as shown by the footprints and mud cracks, so C is oldest, and F the youngest of these. B is above the unconformity above all of C, D, E, and F, so is the youngest of these five.

Which formula describes the chemical changes that occur and release energy when you start with plant material and then burn it in a fire or "burn" it in a stomach?

CH2O + O2 → CO2 + H2O

Sediment is changed to sedimentary rock by:

Cementation by hard-water deposits, intergrowth of new minerals, and squeezing under the weight of additional sediment.

The United Nations, under the auspices of the Intergovernmental Panel on Climate Change, has attempted to assess the scientific understanding of how greenhouse-gas emissions will affect the climate, and thus people. The UN reports show that if we continue on our present path, burning fossil fuels at a faster and faster rate:

Climate will change, primarily getting warmer, and those changes will primarily hurt poor people in warm places, but the climate changes are primarily being caused by wealthier people in colder places.

Among fossil fuels:

Coal is made by heating of woody plant material, and oil is made by heating of algae.

When considering the land surface:

Deposition of sediments occurs in only a few places, with erosion or nondeposition occurring in most places to produce unconformities, and one must piece together geologic history from rocks in many places.

To get gas from the Marcellus shale, drillers:

Drill into and then along the shale, and then pump in high-pressure fluids to fracture the rock and release the gas.

You are asked to assign as accurate a numerical age as possible (how many years old) to a sedimentary deposit. You would be wise to use:

Either counting of annual layers or radiometric techniques if the deposit is young (less than about 100,000 years), and radiometric techniques if the deposit is old (more than about 100,000 years).

Most U.S. beaches are shrinking or encroaching on the land rather than growing or moving seaward, so the land of the U.S. is getting smaller, not bigger. Causes include:

Global sea level is rising, covering more land.

Which is the oldest fault:

I I is cut by J, so I is older than J. And with reference to K, both I and J can be shown to be older than H.

Using only uniformitarian calculations from the thickness of known sedimentary rocks, likely rates at which those rocks accumulated, and features in and under those sedimentary rocks, geologists working two to three hundred years ago estimated that the Earth:

Is more than about one-hundred-million years old.

The above picture is from the Escalante-Grand Staircase National Monument. The pink arrows point along some interesting features. What are they?

Joints, formed when the sedimentary rocks were broken by physical-weathering or other processes.

What is accurate about the scientific results learned by counting annual layers in ice cores?

Many tests show that some ice cores have reliably preserved annual layers, and the longest record extends back more than 100,000 years.

Geological evidence based on several radiometric techniques has provided a scientifically well-accepted age for the Earth. Represent that age of the Earth as the 100-yard length of a football field, and any time interval can be represented as some distance on the field. (So something that lasted one-tenth of the age of the Earth would be ten yards, and something that lasted one-half of the age of the Earth would be fifty yards.) On this scale, how long have you personally been alive?

Much less than the thickness of a sheet of paper.

We saw when we studied weathering that physical weathering makes little pieces from big, and that chemical weathering dissolves some things and makes other chunks. The different chemicals went into different places, dissolved or in chunks. When geologists classify sedimentary rocks, the first divisions are based on:

Origin—rocks made from pre-existing pieces are separated from rocks made from precipitation of dissolved things.

You start with some of the right kind of dead material, and heat this material in the right way, perhaps with a little squeezing. As the material changes, you end up with coal, and the name scientists give to the material changes. In order, from coolest (first) to warmest (last) the names given are:

Peat, lignite, bituminous, anthracite.

Many plants are hard to get along with. Imagine crashing pell-mell through a thicket of devil's club (pictured above), in coastal Alaska, to get away from a charging brown bear. The native people use devil's club for medicinal purposes. We now know that:

Plant protection by thorns is supplemented by chemicals that are poisonous to many things that would eat the plants; those chemicals are sometimes harmful to humans (poison ivy, for example) but sometimes beneficial to humans, and have given us many of our medicines.

The above photograph was taken in the Grand Canyon, and shows a cliff that is approximately 30 feet high. What are the rocks in the cliff?

Precambrian metamorphic rocks with some igneous rocks intruded; the folding was caused by mountain-building processes when the rocks were very hot deep in a mountain range.

The geologic time scale is, starting with the oldest and ending with the youngest:

Precambrian, Paleozoic, Mesozoic, Cenozoic.

Fossil fuels are usually formed from:

Remains of formerly living things buried by sediments in regions with little oxygen.

In the two pictures above, I and II, show traces of former life in rocks from the Grand Canyon. Each is "typical";the rocks near sample I contain fossils similar to those shown in sample I, and the rocks near sample II contain fossils similar to those shown in sample II. It is likely that:

Sample I is from higher in the cliffs of the Grand Canyon, and sample II is from much lower, nearer to the river.

Acadia is beautiful even in the rain and fog, but the park still doesn't have many sandy beaches, and this is surely not a sandy beach, the rocks are granite, broken off the granite bedrock. Why aren't there sandy beaches?

Sand is produced or supplied slowly enough, and sand loss to deep water is fast enough, that sandy beaches do not form.

On average around the world:

Sea level is rising, as warming causes ocean water to expand, and glaciers to melt.

In the picture above, the big W is in ocean water, while the little w is in water in a bay cut off from the ocean by the bar indicated by the pink dashed arrow. A stream flows toward the bay along the blue arrow, and coastal bluffs are indicated by the dashed yellow arrow. What probably happened here?

Sediment has been eroded from the land by waves crashing against the bluffs, and the sediment has been transported along the shore by longshore drift to build the bar.

How is sediment related to sedimentary rock?

Sediment is gradually hardened to sedimentary rock by various processes, and the point where the name changes from sediment to sedimentary rock is somewhat arbitrary.

Humans often try to change coastal processes to benefit us. One of the many things we do is to build walls, or groins, or jetties, to interrupt waves and currents and sediment transport. This example is from the coast of Washington. What has happened here?

Sediment transport is typically from the right, causing deposition to the right of the jetty but erosion to the left

Suppose that CO2 in the atmosphere was held at a constant, natural level for a few thousand years. Then, CO2 was added to double the atmospheric level rapidly, and this new, doubled level was maintained for a few thousand years. What was the most likely change in the typical average temperature of the planet?

Temperature before the increase in CO2 was a few degrees lower than temperature after the increase.

What is accurate about the "Law" of Faunal Succession:

The "Law" was developed from the observation that using geologic reasoning to put rocks in order from oldest to youngest also put the fossils in those rocks in order.

We humans are changing the composition of the atmosphere in many ways. Those changes will directly affect the planet's temperature, but the resulting change in temperature will affect other things on the planet that also affect the planet's temperature. Suppose that we could magically change the composition of the atmosphere enough to raise the temperature one degree if all other parts of the Earth system were held fixed, and after the warming, we allowed the other parts of the Earth system to react for a few years or decades. At the end of that time, what would be the total change in the Earth's temperature?

The Earth would end up a few degrees warmer than before the human influence, because positive feedbacks would amplify the original change.

The size of a typical sandy beach, averaged over a few decades, is usually controlled by:

The balance between sand supply from rivers or from coastal erosion, and sand loss to deep water.

Which is not accurate about the Grand Canyon, in Arizona:

The canyon is wider at the top and narrower at the bottom because the river was wider when the region was wetter, and has narrowed as deserts spread recently.

Great Rock really is a great rock on Cape Cod, as shown by Dr. Alley's relatives for scale. The picture doesn't even show all of the rock above ground, and there is as much rock below ground as above. Great Rock sits well north along the Cape, just inland of Coast Guard Beach. Most of the Cape there is sand and gravel. So why is the rock there?

The ice carried the rock here—glaciers carry big as well as little rocks, and can leave big ones even if most of the material carried by the glacier is then sorted in outwash.

The United Nations-sponsored Intergovernmental Panel on Climate Change shared the 2007 Nobel Peace Prize. The information that the Panel has supplied to policymakers includes:

The observed rise in atmospheric CO2 levels has been caused primarily by human fossil-fuel burning, and very likely is causing warming of the climate that is likely to become much larger if we continue our current behavior.

The Landsat above image from NASA shows Cape Cod, Massachusetts. The short yellow arrow indicates sand deposits at Monomoy Island, a great place for bird-watching. The long pink arrow indicates underwater sand deposits. The dotted blue arrow points to the great Outer Beach of the Cape. Based on material presented in this class, what is going on?

The outer beach (dotted blue) is losing sand to Monomoy (short yellow), which is losing sand to the undersea bars (long pink), which are losing sand to deeper water, as the Cape slowly shrinks.

The picture above shows a very hard piece of rock about six inches across, in the Grand Canyon. The surface of the rock looks rather different from the surfaces of many other rocks. What made this odd-looking surface?

The river, which blasted the rock with sand- and silt-laden water during floods; this shows that even hard rocks can be eroded by rivers.

Suppose you wrote a big check to someone to go out into deep water and haul sand up to replenish your private beach along the Atlantic coast. What is this most likely to cause?

The sand will be moved back into deeper water by waves and currents over the next year or years.

Which is younger:

The tree. The tree is growing on intrusion G, which can be shown to be younger than all of the others.

Look at the picture above of a small dam across a stream bed (between the pink arrows) just above one of the trails into Bryce Canyon. When floods happen in the stream bed:

They flow toward the camera; floodwaters have filled the space upstream of the dam and debris has started to cascade over the dam, so the dam is not serving to trap sediment any more.

You are magically able to map where the sand grains go for over a few years on an east coast beach. MOST of the motion is:

Toward and away from the shore with individual waves.

Which is older:

Unconformity L. Unconformity L is cut by fault I, so is older than I. Fault I is cut by fault J, so is older than J. Fault J is cut by unconformity K so is older than K. Unconformity K is cut by intrusion G so is older than G, and intrusion G is cut by fault H so is older than H. Hence, unconformity L is the oldest on this list.

The picture above shows a muddy sandstone that was deposited on a flood plain. Dr. Alley's index finger in the lower left points along a ridge on the surface of the rock (shadows are to the lower right of Dr. Alley's finger and to the lower right of the feature he is pointing along; his finger is above the rock, so the feature must be a ridge and not a trough). The rock is:

Upside-down; you are looking at the side that was facing down toward the center of the Earth when the rock was deposited.

In the photo above, the jetty (which is a big wall, and could also be called a groin) was constructed out from the coast in the state of Washington. The water is shallow very close to the jetty, and deeper as you move away to left, right, or off the end of the jetty at the lower right. Look at the pattern of waves, which tells you that:

Waves go slower in shallower water.

You are dating a lava flow by the potassium-argon system. However, the offspring in this system are leaking out of the minerals. Which is accurate?

You will think that the lava flow is younger than it really is, but you will be able to detect the error by comparing concentrations of offspring from the edges and centers of grains.