How Fast Is Our Campus Changing? A Field Survey of Rates

Investigation question: Which weathering, erosion and deposition processes are at work on our school grounds right now, how fast is each one going, and how long would it take for them to make a change everyone would notice?

Scientific purpose

Students survey the school grounds for real evidence of surface change (a worn step, a root-widened crack, sediment piled at a downspout or curb, a crumbling concrete edge, rills on a bare slope), measure each change with rulers and tape measures, use dates from the school office (year built, year repaved, last cleaning) to turn each measurement into a rate, and then extrapolate: how long until the step wears through, the crack is a hand wide, the gutter fills. The campus becomes a landscape with the same processes as a canyon, running at rates the students measured themselves.

Why this helps students with this chapter

Students can recite that weathering and erosion shape Earth, but they place those processes in canyons and deserts, not where they stand. Measuring a worn step and dividing by the building's age gives a rate of a fraction of a millimeter per year, exactly the kind of rate that carves canyons, and the extrapolation to 'how long until the step wears through' makes the arithmetic of deep time personal. Finding sediment at a downspout and asking where it came from turns the weathering-erosion-deposition chain into something they can walk along.

Standards connections

MS-ESS2-2 (assesses, explaining surface change from the students' own measurements at small spatial scales and human time scales, then extrapolating): Students construct an explanation of how specific processes (frost and root weathering, water erosion, deposition) are changing specific campus features, supported by their own measurements and rates, and extend the reasoning to longer time scales. This is the 'small and slow' end of the PE with student-collected evidence, which the PE's practice explicitly allows.

MS-ESS2-1 (supports, weathering and sedimentation as observable steps in the cycling of Earth's materials): Sediment traced from a crumbling surface to a pile at a downspout is the first two steps of the rock cycle seen in one afternoon; Lesson 17 completes the loop.

Roles (rotate each session)

• Navigator and safety lead: Carries the campus map with the assigned stations, keeps the group inside the assigned areas and away from traffic, and manages the time at each station.
• Measurer: Takes each measurement three times with the ruler, tape or straightedge, calling out the values with units.
• Recorder and photographer: Writes every value in the table, photographs each feature with a ruler in the frame for scale, and sketches the station on the map.
• Rate analyst: Looks up the feature's age on the campus facts table, computes the average, the rate and the extrapolation back in the classroom, and checks every unit.

Materials

Estimated cost: 3 to 10 per class (an estimate; Chalk, zip bags and gloves; rulers, tapes and clipboards are classroom stock. The indoor alternative adds about $8 for a bag of aquarium gravel and a box of chalk.)

Safety

• Stay inside the marked areas and never enter parking lots, driveways, loading zones or streets; stations are chosen away from traffic.
• No climbing on walls, railings, slopes or roofs; measure only what you can reach standing on level ground.
• Wear gloves to handle sediment and wash hands afterward; do not touch broken glass, sharp metal, animal droppings or anything in a storm drain; report hazards to the teacher instead of removing them.
• Sun and heat: hats, water and shade breaks on hot days; on wet days surfaces are slippery, so walk and keep both hands free when moving between stations.
• Groups stay together and within sight of an adult; the navigator checks that all four members are present before leaving each station.
• Chalk marks only on pavement, never on walls, signs or plants; chalk washes off.

Teacher preparation and setup

1. Walk the campus a week ahead and choose four to six stations that show measurable change: a worn step or threshold, a crack in pavement with roots or weeds, a sediment deposit at a downspout, curb or storm-drain edge, a crumbling concrete or brick corner, a bare slope with rills, a rusting railing or sign post. Mark them on a simple map and number them A to F.
2. Get dates from the office or facilities staff: the year each building or walkway was built or last resurfaced, when the grounds were last swept or the gutters cleaned, and the date of the last heavy rain. Enter them on the campus facts table printed on the recording sheet.
3. Measure each station yourself once so you know the expected size of the numbers (a 10 to 25 mm dip in a 40-year-old step, a 5 to 30 mm crack, a few liters of sediment) and can spot wild errors.
4. Define the boundaries students may use and the areas that are off limits (parking lots, loading zones, roofs, drainage channels, any area near traffic) and brief the office that classes will be outside.
5. Assign each group three or four stations in a different order so groups do not pile up at one feature.
6. Prepare the indoor abrasion alternative in case of rain or heat: jars, chalk, gravel and a scale.

Investigation design

Student procedure

1. In class, read the campus facts table and the station list. For each assigned station, predict in the first table what process and agent you expect to find and whether you think the rate will be fast or slow.
2. Station A (worn step or threshold): lay the straightedge across the step from edge to edge where the wear is deepest. Measure the gap between the straightedge and the lowest point of the dip with the ruler, three times at slightly different spots. Record all three in millimeters. Mark the deepest spot with chalk for future classes.
3. Station B (sediment deposit): find the pile of sand, soil or grit at a downspout, curb or drain edge. Measure its length and width with the tape and its thickness at three points with the ruler. Collect one spoonful in the bag and note its color and grain size. Look uphill or up-gutter and write where the material most likely came from.
4. Station C (crack with plants): measure the crack's width at its widest point three times and its total length once. Note what is growing in it and whether the edges are crumbling.
5. Station D (crumbling corner, flaking paint or rust): measure how far the damaged zone extends from the original edge or surface, three times. Note whether the damage is chemical (rust, flaking, dissolving) or physical (chips, cracks).
6. At every station, photograph the feature with the ruler in the frame, sketch its location on the map, and write the agent you think is responsible (water, ice, wind, gravity, living things, chemical reaction, people and vehicles).
7. Back in class, average the three measurements for each station. Find the feature's age or the time since the last cleaning on the campus facts table. Compute the rate: average change ÷ time, in millimeters per year (or, for the sediment pile, liters per year from length × width × thickness ÷ 1,000 for cm³ to liters).
8. Extrapolate for each station: choose a change everyone would notice (the step worn through at 150 mm; the crack 100 mm wide; the gutter or a 20-liter bucket full of sediment) and compute how long it takes at your rate: target ÷ rate.
9. Answer the analysis questions individually, then write your explanation of how the campus is changing, which processes are involved, how fast each one is, and what would have to be true for your long-term predictions to come out right.

Expected observations

• A concrete or stone step 30 to 60 years old typically shows a wear dip of 5 to 25 mm at the center of the tread, giving rates on the order of 0.1 to 0.5 mm per year; a wooden threshold wears faster.
• Sediment at a downspout or curb after a rainy season is commonly 1 to 10 liters, made of sand and soil the color of nearby bare ground or planters, with an obvious uphill source; the rate is liters per year and dominated by a few storms.
• Pavement cracks with grass or tree roots run 5 to 30 mm wide; where a tree is nearby the crack and the lifted slab are the clearest evidence of living things weathering rock physically.
• Students' predictions usually say the step wears fastest because it is the most used; the measurement shows the opposite, which is a useful surprise for the debrief.

Likely difficulties

• The campus may lack one of the station types; substitute any measurable change (a rusting railing, a sagging retaining wall, lichens spreading on a wall measured against an old photo) and keep the method the same.
• Students measure the straightedge gap at an edge instead of the deepest point; model the measurement once at the first station.
• Ages are uncertain (the step may have been replaced); have students write the age they used and treat the rate as an estimate, which is honest and is what geologists do.
• Unit confusion in the sediment volume (cm³ to liters, 1,000 cm³ = 1 L) and in the cliff extrapolation (meters to millimeters).
• Weather or supervision limits may force the indoor abrasion alternative; keep the same recording tables and treat 'number of shakes' as the time variable.

Structured debrief

1. Put every group's rates on the board by station. Ask why groups that measured the same step got different rates: where the straightedge was laid, how the dip was read, the age used. Then ask what geologists do about this (take many measurements, report a range, say what the rate depends on). The chalk marks mean next year's class can measure the same spots and add a second data point in time.
2. Rank the campus processes by rate. Typical results: sediment deposition at a downspout is the fastest (liters per year after a few storms), a root-widened crack next (millimeters per year), the worn step slowest (tenths of a millimeter per year). Point out that the worn step's rate is in the same range as the rates that carve canyons, and that the difference between a step and a canyon is time, not process.
3. Walk the extrapolation: a step wearing at 0.4 mm/yr takes about 375 years to wear through 150 mm, and would take about 750,000 years to remove a 300 m cliff. Then ask what the extrapolation assumes and why the real answer differs: use changes, surfaces get repaired, rain and frost vary. Connect to the Grand Canyon's debated age: the same uncertainty, on a bigger scale.
4. Close with the chain: at Station B the sediment came from somewhere (weathering of a surface upslope), traveled (erosion by runoff) and stopped (deposition where the water slowed). Ask students where it goes next if nobody sweeps it, and what the campus would look like in a thousand years if maintenance stopped.

Recording sheet: what students fill in

Lab 3 recording sheet: How fast is our campus changing?

Fill in the predictions before you go outside. At each station record three measurements with units, the agent, and a sketch on the map. Back in class complete the rate table, the extrapolation and the questions.

Analysis questions: answer key

Individual evidence of learning

Each student submits their own prediction table, field measurement table, rate-and-extrapolation table, station map and written answers to q1 through q9. The rate table and q3 and q4 are the evidence for the rate target; q9 is scored against the criteria as evidence toward MS-ESS2-2.

Assessment criteria

Accessibility adaptations

• Assign stations along accessible routes and at reachable heights; a student who cannot kneel can be the rate analyst or photographer while a partner measures at ground level.
• Provide a large-print recording sheet, a tape measure with high-contrast markings and a straightedge with a pre-marked center line.
• Allow the explanation (q9) to be recorded as a spoken 'site report' over the station map; allow the map to be built on a printed campus photo with stickers.
• Offer a bilingual word strip for the process and agent columns and a filled example row in the rate table showing the unit chain.

Low-cost alternative

If the field survey cannot run (weather, heat, supervision), do the indoor abrasion version: put one weighed piece of sidewalk chalk and about 100 g of aquarium gravel in a lidded jar with 100 mL of water, shake 100 times, dry the chalk briefly on a paper towel, and weigh it; repeat for three rounds of 100 shakes. Compute the mass lost per 100 shakes, then extrapolate how many shakes would remove the whole stick and how far a river carrying the chalk would have to tumble it. Everything needed costs under $8 per class and the same tables apply with 'shakes' in place of years.

Model limitations

Campus rates are averages over the feature's whole life and assume the age from the office is right and nothing was repaired; a replaced step or a recent sweeping makes the rate wrong in a way the students cannot detect on one visit. Human use (feet, carts, vehicles) is an agent that does not act on natural cliffs, so the step rate is not a natural weathering rate even though the arithmetic is the same. The extrapolations assume constant rates, which the lesson itself says is not guaranteed. The activity has not been physically tested by the authors; the sizes and rates in expectedObservations are typical values and depend on the campus, its materials and its climate.

Teacher notes

Grade rates on the student's own measurements and the age they wrote down, not on a target number. If the campus facts are uncertain, accept a stated assumption ('we used 40 years because the office said the walkway dates from the 1980s'). The step-versus-cliff extrapolation in q4 is a reasoning exercise; make sure students say in q7 or q9 that feet are not a natural agent and that the rate transfer is a thought experiment. Keep the chalk-marked spots and this year's data so next year's class can measure again; a two-year difference is the first direct measurement of a rate the school can make.