Click on this link if you would like to see all of the blacktop

Click on this link if you would like to see all of the blacktop

Question
Assessment

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Introduction
Geology is happening all around you, right now—and you’re paying through the nose for it. Nature breaks rocks, including the funny-looking human-made ones
we call roads. The typical US motorist spends almost $200 in gas taxes per year to repair roads, the truckers pay more, and we’re still not keeping up with the
damage. Dr. Alley needs to keep trapping the groundhogs that burrow under his house, so they don’t undermine it and cause structural damage (which really can
occur!). People do die in landslides. Soil washes off farmer’s fields, and the next year’s crop needs more expensive fertilizer to replace what was lost. By
understanding what is happening, we can save money and lives. And, we can begin to comprehend the processes that shaped the planet.
The assignment in Exercise 2 is for you to notice what is happening around you geologically. Look, see, and understand. Unfortunately, we haven’t figured out
how to give you credit for looking, and we can’t tell whether you’re really looking in the right places. So, we’re going to take you on a tour, by showing you
pictures of results of geologic processes that happened recently, together with some background information. Then, we’ll ask you some questions. Note that if
your friend just did this exercise, they may have had questions that looked similar but had very different answers—there are different versions of a question about
what is, or what isn’t, so copying what your friend did may give you a very bad grade. The material here is easy enough that you’re much better off doing it, and
that way you’ll be ready because we’ll build on this later in the semester.
You will only get one chance to submit this exercise so be sure to review your answers carefully before submission. You can, however, save your answers as long
as you do not submit them first. Do not forget to hit the submit button when you are finished. This exercise will NOT automatically submit since there is no time
limit (except to submit it by the due date shown on the calendar). This exercise will be graded automatically.
So, let’s head off down the road. Or the bike path. All of these pictures were taken one day on Dr. Alley’s bicycle ride to Penn State’s University Park campus.

Question 1: Blacktops
First, examine blacktop pictures 1-6. All six are “blacktop”, not concrete or brick or something else, and please assume that all of them were similar when new,
blacktop is blacktop, and any differences you see have been caused by events since the blacktop was laid down. The pictures are in approximate order of the year
in which the blacktop was installed, with the road 1 built most recently, the bike trail 2 older, the road 3 and 4 built before the bike trail, and the nearly-abandoned
road 5 and the nearly-abandoned driveway 6 built before 3 and 4, probably with the driveway oldest. The roads 1, 3 and 4 are roads, so they are driven on a lot
more than the driveway or the bike trail, but they’re not the main street through town. We’re going to make a few educated guesses about ways that geology
works, based on what we see in these pictures, what we know about roads versus bike trails or driveways, and what we know about the world.

Blacktop #1: Cracks in blacktop, Puddintown
Blacktop #2: Crack in blacktop, bike trail. There Blacktop #3: Crack in blacktop, edge of Big
Road. The cracks are especially common where the are no trees nearby, no heavy loads have been
Hollow road. Cracks in the road are most
wheels drive.
driving on this, and there are very few other cracks commonly at the edge, or under the wheel tracks.
nearby.

Blacktop #4: Crack in blacktop, Big Hollow Road.
The road is slanted here, and the broken-up part
may be sliding downhill a little. Notice that the
cracks are damp and plants are growing in some
cracks. The township has patched this, at least

Blacktop #5: A small section of road off
Blacktop #6: Abandoned blacktop driveway in
Houserville Road, no longer regularly used, but
Houserville. This is a little hard to even recognize
rather old for blacktop. Notice that to the upper
as a driveway.
right and left the blacktop is almost completely
gone. Some cracks are damp here, too, with plants

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twice, but is still losing.

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growing in some.

Click on this link if you would like to see all of the blacktop pictures in a new window. Once you look at the pictures and read the
corresponding text, come back into ANGEL to answer questions one and two.
1.

Blacktop #1: Cracks in blacktop, Puddintown
Blacktop #4: Crack in blacktop, Big Hollow Road.
Road. The cracks are especially common where the The road is slanted here, and the broken-up part
wheels drive.
may be sliding downhill a little. Notice that the
cracks are damp and plants are growing in some
cracks. The township has patched this, at least
twice, but is still losing.

Blacktop #5: A small section of road off
Houserville Road, no longer regularly used, but
rather old for blacktop. Notice that to the upper
right and left the blacktop is almost completely
gone. Some cracks are damp here, too, with plants
growing in some.

Compare pictures 1, 4, and 5. These three pieces of blacktop road are within a mile of each other, and have experienced similar traffic (except that after 5 fell
apart, people quit driving on it). A really good hypothesis based on these is that:
A) Blacktop is self-healing, so the cracks that the workers made installing the blacktop later were filled in when the blacktop softened under the hot
summer sun.
B) Damage accumulates with time, and these pictures prove that time is the only thing that affects the quality of blacktop.
C) Damage accumulates with time, so that older blacktop is more broken up.
Question 2: Blacktop
Compare pictures 1 and 2, showing a newer road with more cracks, and an older bicycle trail with fewer cracks.

Blacktop #1: Cracks in blacktop, Puddintown
Blacktop #2: Crack in blacktop, bike trail. There
Road. The cracks are especially common where the are no trees nearby, no heavy loads have been
wheels drive.
driving on this, and there are very few other cracks
nearby.
2.

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:
A) Bicyclists aren’t as heavy as cars, and the extra stress from heavier things tends to crack blacktop.
B) Bicyclists concentrate all their weight on skinny tires, breaking the blacktop quickly.
C) Bicycles spread oil on the trail that keeps it from cracking.

Question 3: Gravestones
Next, look at the gravestone pictures 1-6. We will call all of the stones granite, marble or sandstone (some of the marble ones are limestone or dolomite, and
some of the granite are granodiorite, but we’ll keep it simple, because the marble and limestone and dolomite are similar to each other, as are the granite and
granodiorite). These are in the same cemetery. We know enough about stone-carving history that all of the stones would have had similarly clear and deep dates
initially. We chose good-looking stones to show you, and for which we could get clear pictures of the date without showing names or anything that anyone might
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not want us to use in a geology class. If you walked around the cemetery, you would find even older granite stones that have clear dates, and not-quite-so-old
marble stones that are already hard to read, with sandstone in-between. Thus, you may accurately assume that these pictures show an old and a new granite
gravestone, an old and a new marble gravestone, and an old sandstone gravestone (there were no new sandstone gravestones, and very new few marble
gravestones; almost all are granite now).

Gravestone #1: Granite, 2010. The grass stuck to Gravestone #2: Granite, 1914. Notice that the
the stone was thrown there by the lawn mower;
carving is still clear and sharp. Letters are often
ignore the grass (you’ll see some in other pictures, about 1/8 inch (3 mm) deep.
and should ignore it there, too), and notice that the
carving is clear and sharp.

Gravestone #4: Marble, 1856? (the “18” on the
left and “6” on the right are evident; not positive
about the “5”. Notice that the carving is almost
totally gone.

Gravestone #3: Marble, 2002. Notice that the
carving is clear and sharp.

Gravestone #5: Sandstone, 1843. The clarity of
Gravestone #6: Sandstone, 1843. This is the
the numbers is somewhere between the granite and same stone as in gravestone picture #5. The stone
the marble. But, check the next picture.
is splitting, something like sheets of paper on a
tablet. The marble and granite did not show such
splitting.

Click on this link if you would like to see all of the gravestone pictures in a new window. Once you look at the pictures and read the
corresponding text, come back into ANGEL to answer questions three and four.
3.

Think about the numbers shown by these pictures, and about the text given above. The best hypothesis is that:
A) The different stones wear away at different rates, with sandstone fastest, marble slowest, and granite in-between.
B) The different stones wear away at different rates, with granite slowest and marble fastest.
C) 1914 was a bad year, and 1843 a good year.

Question 4: Gravestones
Look at gravestone picture 6, and continue with gravestone pictures 7 through 9, reading the descriptions.

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Gravestone #6: Sandstone, 1843. This is the
Gravestone #7: This is an old granite stone.
same stone as in gravestone picture #5. The stone Notice that a chip is missing from the corner.
is splitting, something like sheets of paper on a
tablet. The marble and granite did not show such
splitting.

Gravestone #8: This is an old marble stone
Gravestone #9: This is lichen growing on an old
(1860, we believe, although hard to read the last
granite stone. Simply looking at this stone won’t
digit). Notice that a chip is missing from the corner. tell you what the lichen is doing, but we
independently know that lichens tend to take rocks
apart chemically to get useful nutrients to use in
growing. If we carefully removed the lichen, we
would find that the rock beneath has lost some
chemicals and gained others, as compared to the
rock that isn’t under the lichen (we didn’t want to
upset anyone by scraping away at the gravestone,
so we ask you to take our word on this one). If you
go back and look, there are lichens of other types
on all of the old stones. But, some of the numbers
have been worn away without lichens, so other
mechanisms must be active.
Click here to see all nine(9) pictures of gravestones in a pop up window. Once you look at the pictures and read the corresponding text, come
back into ANGEL to answer question four.
4.

Erosion of the stones—loss of rock material—has been occurring. The pictures, and their captions, show that:
A) Chemical action under lichens, and breaking of chunks of rock at corners of stones, are unequivocally the only processes removing rock.
B) Bit-by-bit removal of rock material is the only mechanism of erosion.
C) Removal of chunks of rock, chemical action under lichens, and perhaps other mechanisms of bit-by-bit removal of rock material contribute to erosion.

Question 5: Chemicals
Next, look at pictures Chemical 1, 2 and 3, and read the captions. We noted in the previous question that evidence (which we haven’t actually shown you)
demonstrates that lichens promote chemical alteration of rocks. But, the marble gravestone in particular seems to have worn away in places where there aren’t
lichens, and there aren’t piles of little pieces of marble at the bottom of the stone. This might suggest that other chemical processes are attacking the rocks, and
especially the marble, perhaps dissolving them in rainfall. The picture Chemical 1 shows and describes things that are related to concrete, which is in some ways
chemically similar to marble. The pictures Chemical 2 and 3 show other evidence of chemical changes going on in other types of rocks.

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Chemical #1: This rather strange picture shows a
crack in the roof of a drainage tunnel under Fox
Hollow Road just north of Penn State’s Beaver
Stadium. Rainwater picks up carbon dioxide from
the air, and possibly acid rain from coal-fired electric
plants, making a weak acid. When the weak acid
hits limestone, or marble, or cement, it dissolves
some of the rock chemically. This is how caves
form, and other changes happen. If the water then
evaporates, or loses some carbon dioxide back to
the air, a cave formation can be deposited. The
picture shows a “cave formation” growing along a
crack in the roof of the tunnel. Thus, chemical
processes can dissolve rock, and can also deposit
rock. The chemical composition of the cave
formation is the same as clam shells and many
other shells (calcium carbonate), which may
suggest what eventually happens to these
chemicals if they stay in the water rather than being
left behind as cave formations.

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Chemical #2: The blacktop on the bike path has
small stones in it. This one contains a piece of iron
pyrite, the gray pebble surrounded by the dark ring
of rust near the center of the picture. Iron pyrite
produces acid mine drainage from some old strip
mines and some other places, because it contains
sulfur (which eventually becomes sulfuric acid) as
well as iron (which here is becoming rust). The top
of the iron-pyrite-bearing pebble is lower than the
tops of the materials around it.

Chemical #3: This is a “concretion”, a big ball that
formed in a layer of shale, and now sits outside of
the Deike Building on Penn State’s University Park
campus. This contains some pyrite, and the rusting
of that pyrite is contributing to the break-up of the
concretion. Many rocks contain a little pyrite, and
nature deals with it, but too much of it can cause
environmental problems.

Click on this link if you would like to see all of the chemical pictures in a new window. Once you look at the pictures and read the
corresponding text, come back into ANGEL to answer question five.
5.

Based on what you have seen and read, the processes that are changing the gravestones include:
A) Physical alteration only—breaking off of chunks of rock.
B) Chemical alteration only—dissolving in rainwater.
C) Physical and chemical alteration, including many chemical processes such as rusting and dissolving in rainwater and beneath lichens.

Question 6: Corners
You saw back in gravestone pictures 7 and 8 that the gravestones typically lost chunks from corners rather than from the middle regions of faces. Pictures Corner
#1 and Corner #2 show similar things, with chips missing from the corner of a curb, and from the edge of a road.

Corner #1: This is a curb in front of the Penn

Corner #2: This is the edge of Pastureview Road

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Stater. Notice that the corner has been chipped in
several places (the light-colored places).

on the University Park Campus. You can see in the
center where chunks of blacktop have broken off of
the pavement (which is on your left).

Gravestone #7: This is an old granite stone.
Notice that a chip is missing from the corner.

Gravestone #8: This is an old marble stone
(1860, we believe, although hard to read the last
digit). Notice that a chip is missing from the corner.

Click on this link if you would like to see all of the corner pictures in a new window. Once you look at the pictures and read the corresponding
text, come back into ANGEL to answer question six.
6.

After looking at the images above and reading their captions, take a look at this cartoon drawing of a gravestone. The big “F” is in the middle of the face of
the gravestone, and the big “C” points right to a corner of the graveston. The pictures show that the “C” is more likely to be knocked off than the “F”. Why?
A) The C is supported by neighbors on only one side, but the F is surrounded by neighbors helping hold it in.
B) The C can be hit from more sides, and the C has fewer neighbors helping hold it in.
C) The C can be hit from two sides, and the F from only one side.
Question 7: Sliding
Next, peruse the pictures labeled Slide 1 through 6, because they talk about things sliding or rolling downhill, not because they are “slides”. Chipmunks and
groundhogs have loosened rock and soil that has slid downhill in the first three. The wall shown in the next two is holding back material that seems to have been
pushing by itself—there is no sign of a groundhog or a backhoe pushing the wall out, just a fairly steep slope with plants growing on it, creeping or sliding
downhill. The sixth picture was taken in a place where observation shows that kids like to climb the slope above the bike trail, which may help move the rocks
downhill.

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Slide #2: This is a groundhog hole, with a lot of
Slide #1: This is a chipmunk hole in the cemetery.
loose dirt downhill below the hole (the brown
Slide #3: The dirt from the groundhog hole in the
Notice that the rocks and dirt that the chipmunk
stuff). You can see a blacktop road at the very
previous picture is burying grass here; the big
dug up are almost all to the lower right of the hole,
bottom. The next picture is of the bottom of the
pieces have slid to the bottom.
which is the downhill side.
dirt that the groundhog dug up and threw downhill.

Slide #4: This old, lichen-covered wall is along the
same hill that the groundhog was digging in. To
guide your eye, we’ve drawn a line along the
bottom of the wall. Notice the bulge. You may
notice that the stones look less regular in the bulge,
and that there are a few that are light-colored (end
of the yellow arrow) because they lack lichens. The
next picture is taken looking along the yellow arrow.

Slide #5: We’re looking at the bulge from the
other side now, with the irregular, light-colored
rocks visible. The wall was pushed out, and
eventually failed, and someone has reconstructed
the wall, rolling some of the rocks over in the
process so that their non-lichen-colored sides are
on top.

Slide #6: The big orange “P” is a pillar of a
freeway bridge over a bike trail. The pink line
guides your eye along the edge of the loose rocks,
which have been rolling out onto the bike trail on
either side of the pillar but not so much right where
the pillar is. Notice that the rocks cover a very steep
slope. In the lower left, there are loose rocks under
the plants (hard to see, but they’re there). Notice
that there the rocks aren’t rolling out into the bike
path.

Click on this link if you would like to see all of the slide pictures in a new window. Once you look at the pictures and read
the corresponding text, come back into ANGEL to answer question seven.
7.

Loose material can move downhill as it is pulled by gravity, eventually changing how steep slopes are and causing other changes. Some things you can
correctly infer from looking at the pictures shown here are:
A) Once you get grass or other plants growing on top, the downhill motion stops.
B) Grass or other plants growing on top tend to reduce the downhill motion, but the slow bulging of the wall suggests that downhill motion can occur even
with a grassy slope.
C) The weight of grass tends to move slopes downhill faster, so there is more motion under grass than in bare-soil places.

Question 8: Wash
Now, look at the four “Wash” pictures, showing evidence of running water washing loose material across human-built things. Note that these slopes are not very
steep, and generally not nearly as steep as in the “Slide” pictures.

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Wash #1: A side bike path comes in from the left
at the bottom of the picture to meet the main bike
path. Cyclists cutting the corner short (notice the
tracks in the mud just to the left of the arrow) are
helping keep the grass from covering the dirt just
there. You can see that there is a “plume” of dirt
that has washed away from this bare place as
shown by the arrow, and heads downhill away from
us, angling across the bike trail towards Slab Cabin
Run, which is just out of the picture on the far
right.

Wash #2: The pile of dirt is used for maintenance
of the nearby baseball diamond at Spring Creek
Park. Kids play on the pile, birds take dust baths on
it when people aren’t around, and it is otherwise
disturbed. When rain falls, the water runs towards
the camera, around the parking bumper and out
into the grass to the left. Notice the trail of dirt
that the water has washed with it.

Wash #3: Rainwater running toward the camera
along the side of the road has washed gravel from
the shoulder into the grass on the right, and on
towards the camera across the driveway in the
foreground. The Township pays people to add
gravel occasionally, to prevent a major dropoff
developing that could cause cars to wreck if a
wheel dropped off the edge.

Wash #4: In the Penn State agricultural lands
north of the Penn Stater, boards have been placed
across steeply sloping gravel roads to trap the loose
rocks washed by rainwater. The hill slopes towards
the camera. Rocks have piled up against the “dam”
on the far side as high as the top of the board,
clean water flows over and has eroded a little on
the near side, creating the dropoff we see, as
shown by the arrows. These “dams” work, but they
are far from perfect.

Click on this link if you would like to see all of the wash pictures in a new window. Once you look at the pictures and read the corresponding
text, come back into ANGEL to answer question eight.
8.

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) Downhill motion is relatively uniform in time, but only a few places contribute.
B) A lot of downhill motion of material occurs over relatively short times (when it’s raining), but all places contribute equally.
C) 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.

Question 9: Trees
Next, look at the pictures of sidewalks and a bike trail near trees. We have seen that there are cracks unrelated to tree roots. But, the cracks in these pictures are
rather clearly related to tree roots. A scientist seeing a crack near a tree makes the hypothesis that the tree’s roots caused it. But, for this to be science, you
would do some hypothesis-testing. Is there really a root under the crack? Is the occurrence of cracks near tree roots purely coincidental, or are there more cracks
near trees than you’d expect based on the number of sidewalks, the number of cracks and the number of trees we see? Do we understand the mechanisms? Can
tree roots generate enough “oomph” to do the job? This one is pretty obvious, but real science never stops there.

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Tree #1: Cracks in sidewalk and curb around an
elm tree on Burrowes at University Park.

Tree #2: Cracks in sidewalk and curb around an
elm tree on Burrowes at University Park.

Tree #3: Cracks in bike path below Sunset Park,
State College.

Click on this link if you would like to see all of the tree pictures in a new window. Once you look at the pictures and read the corresponding
text, come back into ANGEL to answer question nine.
9.

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.
A) True
B) False

Question 10: Office Walls
Finally, consider this last picture of cracks in the wall of Dr. Alley’s office. Click on this link if you would like to see a larger image.

10. Now consider the following statement: “At least we don’t need to worry…