HS-ESS2-1NGSS*ScienceEarth and Space ScienceGrades 9-12
HS-ESS2-1: Modeling How Earth Builds and Wears Down Landforms
In plain English: HS-ESS2-1 is the NGSS high school performance expectation that asks students to develop a model showing how Earth's internal processes (volcanism, uplift, seafloor spreading) and surface processes (weathering, mass wasting, erosion) work at different sizes and speeds to form continental and ocean-floor features. It is usually taught in Earth and Space Science.
Develop a model to illustrate how Earth's internal and surface processes operate at different spatial and temporal scales to form continental and ocean-floor features.
Clarification Statement: Emphasis is on how the appearance of land features (such as mountains, valleys, and plateaus) and sea-floor features (such as trenches, ridges, and seamounts) are a result of both constructive forces (such as volcanism, tectonic uplift, and orogeny) and destructive mechanisms (such as weathering, mass wasting, and coastal erosion).
Assessment Boundary: Assessment does not include memorization of the details of the formation of specific geographic features of Earth's surface.
Next Generation Science Standards · Disciplinary Core Idea: Earth's Systems · Official standard
Students build and test models of how Earth's surface gets its shape. Internal processes driven by Earth's heat (seafloor spreading, subduction, volcanism and tectonic uplift) build features up. Surface processes driven by water, ice, wind and gravity (weathering, mass wasting and erosion by rivers and waves) wear them down. Students compare these processes by size and by rate, turn rates into times with rate × time = change, and use a cross-section model, a sand-tray model and a simple step-by-step computer model to explain continental features (mountains, valleys, plateaus, sea cliffs) and ocean-floor features (ridges, trenches, seamounts).
The NGSS Clarification Statement says: "Emphasis is on how the appearance of land features (such as mountains, valleys, and plateaus) and sea-floor features (such as trenches, ridges, and seamounts) are a result of both constructive forces (such as volcanism, tectonic uplift, and orogeny) and destructive mechanisms (such as weathering, mass wasting, and coastal erosion)." The Assessment Boundary says: "Assessment does not include memorization of the details of the formation of specific geographic features of Earth's surface." So students never memorize how one named place formed: every feature on this page is generic or invented, every data set is invented for teaching with realistic rates, and the goal is a model that works for any mountain range or sea floor. Students do the practice of developing a model: they draw it, run it, test it against data and name its limits.
Learning Objectives
By the end of this lesson, students will be able to:
Classify processes that shape Earth as internal or surface and as constructive or destructive, and give each a typical spatial and time scale
Use rate × time = change, with unit conversions such as 1 mm/yr = 1 km per million years, to compare processes that act at different speeds
Develop and use a cross-section model that shows how internal and surface processes together form continental and ocean-floor features
Run a simple uplift-and-erosion model, explain why a mountain range can reach a steady height, and critique what the model leaves out
Prior Knowledge Required
Students should already be comfortable with:
How geoscience processes change Earth's surface at different time and spatial scales MS-ESS2-2
Evidence of plate motion from rocks, fossils, continental shapes and sea-floor structures MS-ESS2-3
The rock cycle and the energy that drives it MS-ESS2-1
Unit rates and converting between metric units and powers of ten
Project a photo of any mountain range that meets the sea. Give students two minutes alone, then two minutes with a partner.
Warm-Up Prompt
"List everything that could make this range taller and everything that could make it shorter. Next to each item, guess how long it takes to make a change you could see: seconds, years, thousands of years or millions of years."
Sort the class list into two columns on the board, "builds up" and "wears down". Keep it posted: students add rates to it during the lesson. Students often list landslides and earthquakes but forget slow, steady processes such as uplift and river erosion.
Direct Instruction15-20 minutes
Two engines and many scales. Internal processes get their energy from Earth's interior heat: magma rising at a ridge makes new ocean floor, a sinking plate forms a trench, and collisions and volcanism raise mountains. Surface processes get their energy from sunlight (which drives the water cycle and wind) and from gravity: weathering breaks rock, mass wasting moves it downhill, and rivers, glaciers and waves carry it away. Every feature is the result of both at once. Scales differ hugely: a rockfall takes seconds and covers meters, an ocean basin takes over 100 million years and spans thousands of kilometers. A handy conversion: 1 mm/yr = 1 km per million years (Myr), and 1 cm/yr = 10 km/Myr. Walk through Diagram 1, then the examples.
Ocean floor: a spreading ridge
Invented magnetic data from a mid-ocean ridge: the edge of a magnetic stripe lies 60 km east of the ridge axis, and the rock there formed 2.0 million years ago.
Result: Half-spreading rate = 60 km ÷ 2.0 Myr = 30 km/Myr = 3.0 cm/yr. If the west side matches, the plates separate at 6.0 cm/yr, and a strip of new ocean floor 120 km wide formed in 2.0 Myr.
Continent: uplift against erosion
A block of crust rises 3.0 mm/yr while weathering and rivers lower its surface by 1.0 mm/yr. Assume both rates stay steady for 1.5 million years.
Result: Net change = 3.0 - 1.0 = 2.0 mm/yr = 2.0 km/Myr, so the surface rises 2.0 × 1.5 = 3.0 km. With no erosion it would have risen 4.5 km.
Ocean floor: a hot-spot volcano chain
Invented ages of volcanoes in a chain: 0, 2.4 and 4.8 million years at 0, 192 and 384 km from the active volcano.
Result: Plate speed = 192 km ÷ 2.4 Myr = 80 km/Myr = 8.0 cm/yr, and the second pair of volcanoes gives the same value. The older volcanoes are extinct and lower: the plate carried them off the hot spot while waves and weathering wore them down.
Coast: wave erosion
Waves cut a sea cliff in soft rock back by 0.50 m/yr, leaving a flat rock platform below sea level.
Result: A platform 5.0 km wide takes 5,000 m ÷ 0.50 m/yr = 10,000 years: fast for geology, slow for people.
Continent: a river canyon
A river cuts down into a slowly rising plateau at 0.20 mm/yr. The canyon is now 1,200 m deep.
Result: Time = 1,200,000 mm ÷ 0.20 mm/yr = 6.0 million years, if the rate stayed steady. The river keeps cutting because uplift keeps raising the plateau above the level the river drains to.
After each example ask: "Which process is internal and which is surface? Which one builds and which one destroys? What is the time scale?" Point out that the same rate equation works for every process: only the units and the scale change.
Guided Practice15 minutes
Build a step-by-step model of a mountain range together. Each step is 1 million years. Uplift adds 1.0 km per step, and erosion removes 25% of the current height per step, because higher, steeper mountains erode faster. The rule is: new height = old height + 1.0 - 0.25 × old height. Fill in the table as a class, then compare with Diagram 2.
Guided practice model: uplift 1.0 km/Myr, erosion 25% of height per Myr
Time (Myr)
0
1
2
3
4
5
6
Height (km)
0.00
1.00
1.75
2.31
2.73
3.05
3.29
Compute each height from the one before it. Why does the height grow by less each step?
Find the height where uplift and erosion cancel: 1.0 = 0.25 × height, so the height is 4.0 km. This is the steady-state height.
Predict what happens if uplift stops after 8 Myr, then check Diagram 2.
Name one thing the model leaves out, for example that uplift is not steady, that rock type changes erosion rates, or that the crust sinks back as erosion removes weight.
Independent Practice15 minutes
Each student draws a labeled cross-section model of an invented coastline: a spreading ridge offshore, a seamount, a trench, a coastal mountain range with a volcano, a river valley and a sea cliff. For each feature, students draw at least one arrow for the process that built it and one for the process that is wearing it down, label each arrow internal or surface, and add a time scale from the rate card below. The rates are typical orders of magnitude, rounded for teaching.
Rate card (typical ranges, rounded)
Process
Type
Typical rate or duration
Seafloor spreading (each plate)
Internal, constructive
1-10 cm/yr
Plate sinking at a trench
Internal
2-10 cm/yr
Uplift of an active mountain range
Internal, constructive
1-10 mm/yr
River cutting into bedrock
Surface, destructive
0.01-1 mm/yr
Sea-cliff retreat (hard to soft rock)
Surface, destructive
0.001-1 m/yr
Landslide
Surface, destructive
seconds to minutes
Collect the drawings. Look for arrows on both sides of every feature and for time scales that match the rate card.
Closure5 minutes
Exit ticket: "An undersea volcano grows until it breaks the sea surface. Later the plate carries it away from its magma source, waves flatten its top, and it slowly sinks below sea level. Name each process as internal or surface, and say whether the final feature belongs to the continents or to the ocean floor." Return to the warm-up list and ask students to add a time scale to every item.
Differentiation Strategies
For Struggling Students
Give a two-column organizer (builds up / wears down) with the energy source written at the top of each column: interior heat, or sunlight and gravity
Provide the unit conversions on a card (1 mm/yr = 1 km/Myr, 1 cm/yr = 10 km/Myr) and start with whole-number rates
Let students trace Diagram 1 and add arrows before they draw their own cross-section
For Advanced Students
Add a term to the mountain model for the crust rising back up as erosion removes weight, and explain how it changes the steady-state height
Ask students to find, in the guided practice model, how long the range takes to reach 90% of its steady-state height
Have students design a way to test a sand-tray model: which variable they would change, which they would measure and how they would keep the rest fixed
Assessment Guidance
What to Look For
Check that every model shows both constructive and destructive processes and names a time scale for each. Look for correct unit conversions (mm/yr to km/Myr) and for students who treat slow processes as unimportant: over millions of years, a rate of a fraction of a millimeter per year removes kilometers of rock. Listen for students who describe how one named place formed from memory instead of using the model: redirect them to the processes and rates.
02
Classroom Activities
3 Activities
1
Rate Cards: Mapping Processes in Space and Time
20 minGroups of 3-4
Groups place 12 process cards on a large chart with feature size (1 m to 10,000 km) on one axis and time to form (seconds to a billion years) on the other, both on powers-of-ten scales. They color each card by process type and mark whether the feature is on a continent or on the ocean floor.
The 12 Cards (typical values, rounded)
Rockfall from a cliff: 10 m, seconds
Landslide on a hillside: 1 km, minutes
Storm erosion of a beach: 100 m, hours to days
Cinder cone built by eruptions: a few hundred meters, years to decades
Delta built at a river mouth: 100 km, thousands of years
Sea cliff retreating by wave erosion: 1 km, thousands of years
Glacier carving a valley: 10 km, tens of thousands of years
River canyon cut into a plateau: 1 km deep, millions of years
Mountain range raised by plate collision: 1,000 km, tens of millions of years
Ocean trench and volcanic arc: 1,000 km, tens of millions of years
Hot-spot volcano chain: 1,000 km or more, tens of millions of years
Ocean basin opened by a spreading ridge: 5,000 km, over 100 million years
Discussion Questions
Do larger features generally take longer to form? Which cards fit that trend least well, and why?
Which cards are driven by interior heat, and which by sunlight and gravity? Where on the chart does each group sit?
Pick one mountain card and one ocean-floor card. Which surface process works against each one?
Modification for Distance Learning
Share the chart as a slide with movable card images. Groups place the cards in breakout rooms and explain one placement in a short recorded comment.
2
Sand-Tray Landscape Model
25 minGroups of 3-4
Groups build a sloping sand surface in a shallow tray. Rain from a paper cup with pinholes cuts channels (surface process), and lifting the high end with one more book stands for tectonic uplift (internal process). Groups measure the depth of the main channel after each of five rain events and the length of the sand fan (delta) at the low end.
Procedure
Pack damp sand into the upper two-thirds of the tray and set the high end on two books. Leave the low end empty as the "sea".
Each rain event: pour 250 mL of water through the pinhole cup, moving it slowly across the top edge. Measure the deepest point of the main channel with a ruler.
Before event 4, add a third book under the high end (uplift). Keep everything else the same.
Safety: wear goggles so sand does not get in eyes, wipe spilled water and sand from the floor at once so no one slips, keep phones and electrical cords away from the water, and wash hands afterward.
Sample Data (invented)
Main channel depth after rain events 1-5: 0.6, 1.0, 1.3, 2.1 and 2.5 cm. Delta length: 3, 5, 6, 9 and 11 cm.
Discussion Questions
Between which two events did the channel deepen the most, and what changed just before it?
In the model, 250 mL of rain cuts a channel in seconds. Which real process does that stand for, and how long would the real change take?
Name two ways the tray is not like a real landscape (for example, real uplift is slow and steady, and real rock is much harder than sand).
Modification for Distance Learning
Students run the same model at home in a baking pan with sand or soil, or they analyze the sample data above and write a claim about how uplift changes erosion.
3
Spreadsheet Model: Mountains That Rise and Wear Down
25 minPairs
Pairs put the guided-practice rule into a spreadsheet: new height = old height + uplift - erosion fraction × old height, one row per million years. They run four scenarios for 20 steps, graph each one and compare the steady-state heights.
Scenarios
A: uplift 1.0 km/Myr, erosion 25% per Myr (the class model)
Scenario B reaches a steady height of 8.0 km and scenario C only 2.0 km. Write a rule that predicts the steady height from the two inputs.
In scenario D, how many million years after uplift stops is the range less than half as high as it was?
Real ranges rarely stay above about 9 km. Which part of the model would you change so it could explain that limit?
Challenge Variation
Adapt the model to a volcano on the ocean floor: it grows while it sits over a hot spot, then the plate carries it away, growth stops, waves erode it while it is near sea level, and it sinks 0.05 km per step. Sketch the height curve before running the spreadsheet.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Cross-Section Model of Building and Wearing Down
A schematic model, not to scale, of an ocean plate sinking under a continent. Green arrows are constructive processes driven by interior heat (spreading, subduction, uplift and volcanism). Red arrows are destructive surface processes (waves, landslides, rivers). Every labeled feature exists because both kinds of process act on it at their own rates.
Diagram 2: A Step Model of a Mountain Range
The guided-practice model, drawn to scale: uplift of 1.0 km per million years, and erosion that removes 25% of the height each million years. The height levels off near 4.0 km, where uplift and erosion cancel. After uplift stops at 8 Myr, erosion alone lowers the range.
04
Homework Assignment
~30 min
HS-ESS2-1 Homework: Building and Testing Landform Models
Directions: All data are invented for practice, with realistic rates. Show every unit conversion (1 mm/yr = 1 km/Myr, 1 cm/yr = 10 km/Myr). For each problem, say which processes are internal and which are surface.
Part 1: Ocean-Floor Features (Problems 1-2)
Magnetic stripe edges on the east side of an invented ridge lie 18, 36 and 54 km from the axis, and their rocks are 0.8, 1.6 and 2.4 million years old. On the west side the same ages lie 16, 32 and 48 km from the axis. (a) Find the half-spreading rate on each side in cm/yr. (b) Find the full spreading rate. (c) At that rate, how much wider does the ocean basin get in 10 million years?
Earthquakes under an invented coast get deeper inland: they are 20, 80, 140 and 200 km deep at 0, 100, 200 and 300 km from the trench. (a) Find how many kilometers deeper the earthquakes get per kilometer inland. (b) Explain what this pattern tells you about the ocean plate. (c) A student says the trench was carved by strong currents on the sea floor. Use the data to critique that model.
Part 2: Continental Features (Problems 3-4)
Use the step model new height = old height + U - r × old height, with U = 0.5 km/Myr and r = 0.20. (a) Starting from 0, find the height after 1, 2 and 3 million years. (b) Find the steady-state height. (c) A wetter climate doubles r. Find the new steady-state height and explain the change in words.
Wave-cut terraces (old beaches) now sit above the sea on an invented coast. Terraces at 40, 80 and 120 m above sea level are 100,000, 200,000 and 300,000 years old. (a) Find the uplift rate in mm/yr. (b) The sea cliff below the lowest terrace retreats 0.2 m/yr. How far has it retreated in the last 5,000 years? (c) Draw a labeled cross-section that shows both processes.
Part 3: Scales and Model Critique (Problems 5-6)
A landslide moves rock 600 m in 2 minutes. A plate moves 5 cm/yr. (a) How long does the plate take to move 600 m? (b) Both processes move rock. Explain why a model of a mountain valley needs both, even though their time scales are so different.
A volcanic island grows by 0.004 km³ of lava per year for 500,000 years while it sits over a hot spot. Waves and weathering remove 0.001 km³ per year from it during the whole time. (a) Find the net volume after 500,000 years, assuming the removal rate applies the whole time. (b) After the eruptions stop, how long would erosion at the same rate take to remove that volume? (c) Name one process the model leaves out and explain how it would change the answer.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Rates and Scales
Correct rate × time calculations with units and conversions for every problem
Correct method with one unit or arithmetic error
Model
Cross-sections and step models show both internal and surface processes, labeled with rates or time scales
Model shows only one kind of process, or labels are missing
Critique and Reasoning
Uses the data to support or reject a model and names a real limitation
States a judgment without using the data
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data are invented, with realistic rates. Use 1 mm/yr = 1 km per million years and 1 cm/yr = 10 km per million years. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which pair shows a constructive internal process and a destructive surface process?
Answer: B
Magma building a volcano is driven by interior heat and adds material; waves cutting a cliff are driven by wind (and so by sunlight) and remove material. Choice A and choice C are both surface processes. Choice D lists two internal, constructive processes, so it has no destructive surface process.
Question 2 of 20 · Multiple Choice
The edge of a magnetic stripe lies 42 km from a ridge axis, in rock that formed 1.2 million years ago. What is the half-spreading rate?
Answer: C
42 km ÷ 1.2 Myr = 35 km/Myr, and 10 km/Myr = 1 cm/yr, so the rate is 3.5 cm/yr. Choice D forgets to convert km/Myr to cm/yr. Choice B doubles the answer, which is the full rate of both plates together, not the half rate. Choice A slips a factor of 10 in the conversion.
Question 3 of 20 · Multiple Choice
Which of these features can form in the shortest time?
Answer: A
A landslide happens in minutes. A deep canyon takes millions of years, a mountain range tens of millions of years, and an ocean basin over 100 million years. Choice D is the slowest and largest feature on the list, the opposite end of the scale.
Question 4 of 20 · Multiple Choice
In a step model, a range gains 0.7 km of uplift per million years and loses 20% of its height to erosion per million years. At what height do uplift and erosion cancel?
Answer: D
At steady state 0.7 = 0.20 × height, so the height is 0.7 ÷ 0.20 = 3.5 km. Choice A multiplies the two inputs instead of dividing. Choice C is the height after the first step only. Choice B adds the two numbers, which have different units.
Question 5 of 20 · Multiple Choice
A volcano in a hot-spot chain is 4.0 million years old and sits 360 km from the active volcano over the hot spot. How fast does the plate move?
Answer: A
360 km ÷ 4.0 Myr = 90 km/Myr = 9.0 cm/yr. Choice C does not convert km/Myr to cm/yr. Choice B slips a factor of 10. Choice D doubles the speed, as if two plates were moving apart.
Question 6 of 20 · Multiple Choice
An invented depth profile across the sea floor goes 4.5, 4.8, 5.2, 8.9, 6.1 and 2.0 km deep, and then reaches the coast of a continent. What feature does the 8.9 km reading most likely show?
Answer: C
A narrow, very deep low next to a continent fits a trench, where one plate sinks under another. A ridge (choice A) and a seamount (choice B) would be shallower than the plain around them, not deeper. The shelf (choice D) is the shallow ledge at the coast.
Question 7 of 20 · Multiple Choice
Rock layers in both walls of a canyon match: the same sequence of layers at the same heights. Which model does this evidence support?
Answer: B
Matching layers mean the rock was once continuous, so something removed the middle: a river cutting down over a long time. Choice C cannot explain why the layers match. Choice A would need the walls to have moved apart by the width of the canyon, and the matching layers show no sign of that. Choice D describes a constructive process, which adds rock instead of removing it.
Question 8 of 20 · Multiple Choice
A plate moves 4 cm/yr. How far does it move in 1 million years?
Answer: B
4 cm/yr × 1,000,000 yr = 4,000,000 cm = 40 km (or use 1 cm/yr = 10 km/Myr). Choice A and choice C are off by a factor of 10 in opposite directions; choice D is off by 100.
Question 9 of 20 · Multiple Choice
A student's model of a mountain range shows only uplift. Which observation can that model NOT explain?
Answer: D
A model with only uplift predicts that ranges keep rising; lower, rounded older ranges need weathering and erosion wearing them down over time. Choices A, B and C all fit a model of uplift at a plate boundary, so they do not show what the model is missing.
Question 10 of 20 · Multiple Choice
In a step model of a mountain range, which change raises the steady-state height?
Answer: A
The steady height is uplift ÷ erosion fraction, so a larger uplift gives a higher steady state. A larger erosion fraction (choice B) lowers it. The starting height (choice C) changes how quickly the model gets there, not where it ends up.
Question 11 of 20 · Multiple Choice
A sea cliff retreats 0.8 m/yr. How long does it take to retreat 2.0 km?
Answer: C
2,000 m ÷ 0.8 m/yr = 2,500 years. Choice A multiplies instead of dividing. Choice B forgets to change 2.0 km into 2,000 m. Choice D slips a factor of 10.
Question 12 of 20 · Multiple Choice
A seamount has a flat top 1.2 km below sea level. Waves planed the top flat while it was at sea level. Since then the plate has carried it away from its magma source, and it has sunk at an average of 0.03 km per million years. About how long ago was its top at sea level?
Answer: A
Time = 1.2 km ÷ 0.03 km/Myr = 40 million years. Waves erode only near sea level (a surface process), so the flat top formed there. Then the plate carried the volcano away from its heat source and it sank as the plate cooled (an internal process). Choice B slips a factor of 10. Choice C multiplies 1.2 by 0.03 instead of dividing. Choice D slips a factor of 10 the other way, and no ocean floor is that old.
Question 13 of 20 · Multiple Choice
A canyon is 750 m deep. The river cut it at a steady 0.25 mm/yr. How long did that take?
Answer: D
750 m = 750,000 mm, and 750,000 ÷ 0.25 = 3,000,000 years. Choice A forgets to change meters into millimeters (750 ÷ 0.25 = 3,000). Choice B slips a factor of 10. Choice C multiplies 750,000 by 0.25 instead of dividing.
Question 14 of 20 · Multiple Choice
Which feature has the largest spatial scale?
Answer: C
The mid-ocean ridge system runs for tens of thousands of kilometers around the globe, far larger than a delta (up to a few hundred kilometers). A dune (choice A) and a landslide (choice D) are meters to kilometers across.
Question 15 of 20 · Short Answer
Invented wave-cut terraces on a rising coast are 15 m above sea level at an age of 50,000 years and 45 m above sea level at 150,000 years. Find the uplift rate in mm/yr, and predict the height of a terrace that formed 250,000 years ago.
The rate is 15 m per 50,000 years (or 45 m per 150,000 years) = 0.0003 m/yr = 0.3 mm/yr. If uplift stayed steady, a 250,000-year-old terrace is at 0.3 mm/yr × 250,000 yr = 75 m. Uplift is the internal process; the terraces themselves were cut by waves, a surface process.
Question 16 of 20 · Short Answer
Rock that formed 1.0 million years ago lies 33 km east and 24 km west of an invented ridge axis. Find the half-spreading rate on each side and the full spreading rate. Is the spreading symmetric?
East: 33 km ÷ 1.0 Myr = 33 km/Myr = 3.3 cm/yr. West: 24 km/Myr = 2.4 cm/yr. Full rate = 3.3 + 2.4 = 5.7 cm/yr. The spreading is not symmetric: the east plate moves away from the axis faster.
Question 17 of 20 · Short Answer
Develop a model in words (or a labeled sketch) of how a trench and a line of coastal volcanoes form where an ocean plate meets a continent. Include one internal process, one surface process, and a time scale for each.
A strong answer: the dense ocean plate sinks under the continent at a few centimeters per year (internal), which bends the sea floor down into a trench. The sinking plate releases water that helps rock above it melt; the magma rises and builds volcanoes over thousands to millions of years (internal, constructive). At the same time rain, rivers and landslides wear the volcanoes down (surface, destructive), from minutes for a landslide to millions of years for a valley. Rubric: 1 point for a correct internal process, 1 for a surface process, 1 for sensible time scales.
Question 18 of 20 · Short Answer
A model range is 3.2 km high when uplift stops. After that, erosion removes 25% of its height each million years. How high is it 2 million years later? Explain why the height never quite reaches zero in this model.
After 1 Myr: 3.2 × 0.75 = 2.4 km. After 2 Myr: 2.4 × 0.75 = 1.8 km. Each step removes a fraction of what is left, so the height shrinks toward zero without reaching it. Real ranges are worn down to low hills or plains, which the model approximates only roughly.
Question 19 of 20 · Short Answer
A student claims: "A mid-ocean ridge is a mountain range pushed up where two plates collide." Describe what data about the rock on the sea floor would show whether the claim is right.
Measure the age of the rock (or map the magnetic stripes) across the ridge. If the rock is youngest at the crest and gets older at the same rate on both sides, the ridge is where new crust forms as plates move apart, which contradicts the collision claim. Heat flow that is highest at the crest also supports spreading.
Question 20 of 20 · Short Answer
A hillside soil creeps downhill at 2 mm/yr. A landslide on the next slope moves 40 m in one minute. How many years does creep take to move soil 40 m? Explain why both belong in a model of how the valley widens.
40 m = 40,000 mm, and 40,000 ÷ 2 = 20,000 years. Creep is slow but never stops, while landslides are fast but rare. Over thousands to millions of years both move large amounts of soil and rock toward the river, which carries it away, so a good model includes both time scales.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-ESS2-1 mean?
HS-ESS2-1 asks students to develop a model that shows how processes inside Earth and processes at the surface, working at very different sizes and speeds, together form the features of the continents and the ocean floor. Internal processes such as volcanism and uplift build features; surface processes such as weathering and erosion wear them down. The code means High School, Earth and Space Science, core idea 2 (Earth's Systems), performance expectation 1.
Is HS-ESS2-1 taught in Earth science or geology?
It is usually taught in a high school Earth and Space Science course, and it can also appear in an integrated science course or a geology elective. The math is rates, unit conversion and simple step-by-step models, which students can do after middle school math.
What is the assessment boundary for HS-ESS2-1?
The official Assessment Boundary says assessment does not include memorizing the details of how specific geographic features formed. Students may see real places as illustrations, but they are assessed on using a model of processes and rates, not on recalling the history of one mountain range or trench.
What is the difference between constructive and destructive processes?
Constructive processes build features up; destructive processes wear them down. Volcanism, tectonic uplift and mountain building (orogeny) are constructive. Weathering, mass wasting (landslides, rockfalls, creep) and erosion by rivers, glaciers, wind and waves are destructive. Every real feature is shaped by both at once.
What are internal and surface processes in Earth science?
Internal processes get their energy from Earth's interior heat and include plate motion, volcanism, earthquakes and uplift. Surface processes get their energy from sunlight, which drives wind and the water cycle, and from gravity, and include weathering, erosion and deposition.
How do students "develop a model" for this standard?
A model can be a labeled cross-section, a physical model such as a sand tray, or a simple computer or spreadsheet model. A good model shows the processes, their direction (building up or wearing down), their rates or time scales, and how they interact. Students should also use the model to explain data and name what it leaves out.
How can processes that take millions of years be studied in class?
Use rates. A rate of 1 mm/yr sounds tiny, but it equals 1 km per million years, so students can turn measured rates into times and sizes with rate × time = change. Physical models such as sand trays speed processes up, and step-by-step spreadsheet models let students run millions of years in seconds.
Why do mountains not keep getting taller forever?
Because erosion speeds up as mountains get higher and steeper. When the erosion rate grows to match the uplift rate, the height levels off. The crust also sinks under the weight of a high range. The step model in this lesson shows the leveling off as a steady-state height.
How is HS-ESS2-1 different from HS-ESS1-5?
HS-ESS2-1 is about modeling how processes build and wear down landforms and sea-floor features. HS-ESS1-5 asks students to evaluate evidence for past and present plate motions, such as the ages of ocean crust. The two share data like spreading rates, but HS-ESS2-1 focuses on the model of processes and scales.
What comes after HS-ESS2-1?
HS-ESS2-3 develops a model of Earth's interior and the mantle convection that drives the internal processes, and HS-ESS3-1 connects landforms and natural hazards such as volcanoes, landslides and coastal erosion to human activity.
07
Related Standards
6 standards
These standards connect to HS-ESS2-1: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-ESS2-2Prerequisite
Explain how geoscience processes changed Earth's surface at varying time and spatial scales
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