HS-ESS1-5NGSS*ScienceEarth and Space ScienceGrades 9-12
HS-ESS1-5: Plate Tectonics and the Ages of Crustal Rocks
In plain English: HS-ESS1-5 is the NGSS high school performance expectation that asks students to evaluate evidence of past and present crustal movement and use plate tectonics to explain the ages of crustal rocks. Students explain why ocean floor gets older away from mid-ocean ridges and why continents hold much older rock. It is usually taught in Earth and Space Science.
Evaluate evidence of the past and current movements of continental and oceanic crust and the theory of plate tectonics to explain the ages of crustal rocks.
Clarification Statement: Emphasis is on the ability of plate tectonics to explain the ages of crustal rocks. Examples include evidence of the ages oceanic crust increasing with distance from mid-ocean ridges (a result of plate spreading) and the ages of North American continental crust increasing with distance away from a central ancient core (a result of past plate interactions).
Next Generation Science Standards · Disciplinary Core Idea: Earth's Place in the Universe · Official standard
Students evaluate evidence that Earth's crust has moved in the past and is moving now, and use the theory of plate tectonics to explain a striking pattern: the ocean floor is young, while continents hold rocks billions of years old. They analyze the ages of seafloor basalt at different distances from mid-ocean ridges, the symmetric pattern of magnetic stripes, GPS measurements of present-day plate motion, and the ages of rock belts across North America. For each line of evidence they ask what it shows, how strong it is, and how plate tectonics accounts for it.
The NGSS Clarification Statement says: "Emphasis is on the ability of plate tectonics to explain the ages of crustal rocks. Examples include evidence of the ages oceanic crust increasing with distance from mid-ocean ridges (a result of plate spreading) and the ages of North American continental crust increasing with distance away from a central ancient core (a result of past plate interactions)." NGSS lists no Assessment Boundary for HS-ESS1-5, so this lesson keeps the focus that statement sets: evidence for the ages of oceanic and continental crust. Drill-core, magnetic, GPS and transect data sets on this page are invented for teaching and follow the published patterns; well-established values, such as the age of the oldest ocean floor, are marked as approximate. Rates use the fact that 1 km per million years equals 1 mm per year.
Learning Objectives
By the end of this lesson, students will be able to:
Analyze seafloor age and magnetic stripe data to find spreading rates and to test whether spreading is symmetric about a ridge
Evaluate how well each line of evidence (seafloor ages, magnetic stripes, sediment thickness, hotspot tracks, GPS) shows past or current crustal movement
Use plate tectonics, including subduction, to explain why oceanic crust is rarely older than about 200 million years while continental crust can be about 4 billion years old
Explain the pattern of North American crustal ages, oldest in an ancient core and younger toward the edges, as a result of past plate collisions
Write an evidence-based explanation that states a claim, cites data and judges its strength
Prior Knowledge Required
Students should already be comfortable with:
Data on fossils, rocks, continental shapes and seafloor structures as evidence of past plate motions MS-ESS2-3
The geologic time scale and how rock layers record Earth's history MS-ESS1-4
Rates as distance divided by time, and converting between km, m and mm
The layers of Earth and the idea that rock is dated with radioactive decay
Show two approximate numbers side by side: the oldest large areas of ocean floor are about 180 million years old, and the oldest known continental rocks are about 4.0 billion years old.
Warm-Up Prompt
"Oceans cover about 70% of Earth, and the planet is about 4.6 billion years old. Why would the rock under the oceans be so much younger than the rock of the continents? Write one possible explanation and one piece of evidence that could test it."
Collect ideas on the board (the oceans formed late, ocean rock wears away, ocean rock is made and destroyed). Tell students they will evaluate evidence for each idea during the lesson.
Direct Instruction15-20 minutes
How plate tectonics sets the age of crust. At mid-ocean ridges, magma rises and cools into new basalt, so the youngest oceanic crust sits at the ridge axis. As the plates on both sides move apart, that crust is carried away and new crust forms behind it: the age of the ocean floor increases with distance from the ridge. When oceanic crust reaches a trench, it is dense enough to sink back into the mantle (subduction), so old ocean floor is continually destroyed. Continental crust is thicker and less dense, so it resists subduction and survives for billions of years. Continents grow at their edges when island arcs, slivers of crust and other continents collide with them. Use Diagram 1 for seafloor ages and Diagram 2 for North America.
Seafloor ages increase with distance from a ridge
Invented drill-core data east of a ridge: basalt at 0, 100, 200 and 300 km from the axis is 0, 4.0, 8.0 and 12.0 million years old.
Result: Rate = 100 km ÷ 4.0 million years = 25 km per million years = 25 mm/yr. The ages rise steadily with distance, as plate spreading predicts.
Magnetic stripes on both sides of a ridge
The magnetic reversal of about 0.78 million years ago is found 39 km west and 41 km east of an invented ridge.
Result: West: 39 ÷ 0.78 = 50 mm/yr. East: 41 ÷ 0.78 ≈ 53 mm/yr. The mirror-image pattern supports crust forming at the axis and moving out both ways; the ridge spreads at about 103 mm/yr in total.
Why the ocean floor stays young
An invented plate carries crust from a ridge to a trench 9,000 km away at 50 mm/yr.
Result: 9,000 km ÷ 50 km per million years = 180 million years, which is only about 3.9% of Earth's 4.6-billion-year age. Crust older than its trip time has already been subducted.
North American crust ages away from an ancient core
A simplified transect (Diagram 2): 2.7 billion years at the ancient core, then 1.85, 1.1, 0.45 and 0.15 billion years at 700, 1,500, 2,200 and 2,900 km.
Result: The ages fall with distance from the core. Plate tectonics explains the pattern: the core is the oldest piece, and each younger belt was added at the continent's edge by a later collision.
Current motion matches the rock record
GPS stations on opposite sides of the ridge from the first example move apart by about 50 mm each year (invented readings).
Result: Past rate from the ages: 25 mm/yr on each side, so 50 mm/yr in total. Current rate from GPS: 50 mm/yr. The rock record and today's motion agree.
After each example, ask: "Is this evidence of past movement, current movement, or both? What would the data look like if the crust did not move?" Point out that a single data set rarely settles a question; the case for plate tectonics is strong because independent kinds of evidence give the same rates and ages.
Guided Practice15 minutes
Pairs analyze invented drill-core ages from two ridges and plot age against distance, then compare their graph with Diagram 1.
Guided practice data: invented seafloor ages at two ridges
Distance (km)
Ridge A age (million years)
Distance (km)
Ridge B age (million years)
0
0.0
0
0.0
50
4.0
150
2.1
100
8.1
300
4.0
150
11.9
450
6.0
200
16.0
600
7.9
Plot age against distance for both ridges on the same axes.
Find each rate as distance ÷ age. Ridge A moves crust away at about 12.5 mm/yr and Ridge B at about 75 mm/yr.
Explain why the slow ridge gives the steeper line on an age-distance graph.
Evaluate: does the data support steady spreading at each ridge? Name the point that fits least well and suggest a reason (measurement error in dating, or a change in rate).
Independent Practice10 minutes
Each student reads an invented summary of a survey: the oldest basalt recovered in one ocean basin is 152 million years old and lies 3,800 km from the ridge, while granite from the neighboring continent is dated at 2.9 billion years. Students (1) find the average rate at which that crust moved away from the ridge, (2) explain in a short paragraph why the continent holds much older rock than the ocean floor, and (3) name one more measurement that would test their explanation.
Expected result: 3,800 km ÷ 152 million years = 25 mm/yr. A strong explanation names spreading at the ridge, subduction at trenches and the low density of continental crust.
Closure5-10 minutes
Exit ticket: "Basalt 60 km from a ridge is 2.0 million years old. If spreading has been steady, predict the age of basalt 150 km from the ridge on the same side, and name one observation that would show spreading is still happening today." (30 mm/yr, so 5.0 million years.) Return to the warm-up ideas and ask which ones the evidence supports.
Differentiation Strategies
For Struggling Students
Provide a rate table with columns for distance (km), age (million years) and rate (mm/yr), with the first row worked out
Give an evidence-rating frame: "This evidence shows ___ movement (past/current). It is strong/weak because ___."
Use a two-color cross-section of a ridge and a trench so students can trace one piece of crust from its formation to its subduction
For Advanced Students
Ask students to find where the spreading rate changed in a data set whose age-distance line bends, and to suggest what could cause the change
Have students compare seafloor age with ocean depth data and explain why older, cooler crust sits deeper
Ask students to evaluate the claim that the oldest ocean floor would be found next to the oldest continent, using the Atlantic as a test case
Assessment Guidance
What to Look For
Check that students compute rates with the right units (1 km per million years = 1 mm/yr) and tell half-rates from total spreading rates. Look for explanations that link each age pattern to a process: spreading for ocean floor ages, subduction for the missing old ocean floor, and collisions for continental belts. Listen for students who think the oceans are simply younger than the continents, or who treat one data set as proof.
02
Classroom Activities
3 Activities
1
Paper Seafloor: Modeling Magnetic Stripes
25 minGroups of 3
Groups feed two paper strips up through a slot in a sheet of cardboard (the ridge) and pull them apart to the left and right. Every 30 seconds they switch marker colors to record a magnetic reversal. They then use the stripes to measure spreading and to evaluate what the model shows and misses.
Procedure
Tape the two strips together at one end and push the joined end up through the 10 cm slot. One student pulls each strip out sideways at a steady 1 cm every 10 seconds; the third student colors the paper as it comes out of the slot.
Switch colors every 30 seconds for 3 minutes, so each side gets 6 stripes.
Scale: 1 cm on the paper = 5 km, and 30 seconds = 0.2 million years.
Safety: use scissors only to trim the strips, and keep the cardboard edge taped so it does not cut hands.
Expected Results
Each stripe is 3 cm wide, which stands for 15 km of crust formed in 0.2 million years: a rate of 75 mm/yr on each side. After 3 minutes, each strip holds 18 cm of paper, standing for 90 km and 1.2 million years.
Discussion Questions
Where is the youngest "crust" on your model, and where is the oldest? How does that match the drill-core data?
The two sides are mirror images. What would the stripes look like if one student pulled faster?
The model shows spreading but not subduction. Why does that make its ocean floor unrealistically old after many minutes?
Modification for Distance Learning
Students do the model at home with two strips of printer paper taped end to end and a slot cut in a cereal box, then post a photo of their stripes with a calculated rate.
2
Evidence Stations: Past and Present Movement
25 minGroups of 3-4
Four stations each hold one invented data set that follows a real pattern. At each station, groups decide whether the data show past movement, current movement or both, rate the strength of the evidence, and write one sentence on how plate tectonics explains it. Groups rotate every 6 minutes.
Stations
Station 1, GPS time series: a station's distance from a fixed marker on another plate grows by 0, 21, 39, 61, 80 and 101 mm over years 0 to 5.
Station 2, sediment on the ocean floor: sediment is 0, 40, 85 and 120 m thick at 0, 200, 400 and 600 km from a ridge that spreads at 20 mm/yr on each side.
Station 3, continental ages: Diagram 2, the simplified North American transect.
Station 4, matching rocks and fossils: rock belts of the same age and type, with the same fossil reptile, on coasts now 4,000 km apart across an ocean.
Discussion Questions
Which station measures motion that is happening now rather than in the past? What rate does it give?
At Station 2, crust at 200, 400 and 600 km is 10, 20 and 30 million years old. Is sediment piling up at a roughly steady rate of about 4 m per million years? What does that add to the case for seafloor spreading?
Which station gives the strongest evidence that the continent grew by collisions, and why?
If the coasts at Station 4 separated at 20 mm/yr on each side (40 mm/yr in total), how long ago were they joined?
Modification for Distance Learning
Post the four stations as slides. Students rate each one on a shared form and discuss the ratings in a video call.
3
Argument from Evidence: A Fixed Ocean Floor or Plate Tectonics?
20 minPairs, then whole class
Pairs test two competing explanations with one numerical prediction. Explanation 1: the ocean floor formed early and has stayed in place. Explanation 2 (plate tectonics): ocean floor is made at ridges and destroyed at trenches.
Task
Deep-sea clay builds up very slowly: assume about 2 m per million years, a typical value for the open ocean.
Predict the sediment thickness on the oldest ocean floor under each explanation. Explanation 1: 4,000 million years × 2 m = 8,000 m (8 km). Explanation 2: about 180 million years × 2 m = 360 m.
Compare with the observation that deep-ocean sediment is typically hundreds of meters thick, not kilometers.
Write a claim, evidence and reasoning paragraph stating which explanation the data support.
Discussion Questions
The prediction under Explanation 1 is more than 20 times larger than under Explanation 2. Why is a large difference in predictions useful when you evaluate two explanations?
What other data would you want before you accepted either explanation?
Challenge Variation
Pairs research the depth of the ocean at increasing distance from a ridge and add a second, independent test to their argument.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Seafloor Age Against Distance at a Slow and a Fast Ridge
Invented drill-core ages from the guided practice, drawn to scale. At both ridges the crust gets older with distance from the axis, as plate spreading predicts. The slope of each line is the reciprocal of the spreading rate, so the slow ridge (about 12.5 mm/yr) gives a steeper line than the fast one (about 75 mm/yr).
Diagram 2: Simplified Ages of North American Crust Away from the Ancient Core
A simplified age transect drawn to scale, with invented values that follow the published pattern: rocks of the ancient core in the Canadian Shield are more than 2.5 billion years old, and belts toward the edges of the continent are younger. Plate tectonics explains the pattern as crust added to the edges by past plate collisions.
04
Homework Assignment
~30 min
HS-ESS1-5 Homework: Evaluating Evidence for Crustal Ages
Directions: All data sets are invented for practice and follow real patterns. Use 1 km per million years = 1 mm/yr. Show each calculation with units, and end every problem with a claim that names your evidence and says how strong it is.
Part 1: Oceanic Crust (Problems 1-2)
Basalt samples east of a ridge are 2.0, 4.1 and 6.0 million years old at 60, 120 and 180 km. West of the ridge, samples at 60, 120 and 180 km are 2.4, 4.8 and 7.2 million years old. (a) Find the rate on each side. (b) Is spreading symmetric? (c) Predict the age of basalt 300 km east of the ridge. (d) What is the total spreading rate?
The magnetic reversal of about 2.58 million years ago is found 77 km west and 80 km east of a ridge. (a) Find the rate on each side and the total spreading rate. (b) At that total rate, how long would it take for the ocean basin to widen by 1,000 km? (c) Explain why the stripe pattern is evidence of past, not current, movement.
Part 2: Continental Crust (Problems 3-4)
On an invented continent, rocks are 3.1, 2.2, 1.4 and 0.6 billion years old at 0, 500, 1,100 and 1,800 km from its center. A student claims: "This continent grew outward over time as other pieces of crust collided with its edges." (a) Describe the pattern in the data. (b) Evaluate the claim with plate tectonics. (c) Name one observation that would weaken the claim.
Two GPS stations on opposite sides of a ridge move apart at 34 mm/yr. Magnetic stripes show crust 3.4 million years old 58 km from the ridge on each side. (a) Find the total spreading rate from the stripes. (b) Compare it with the GPS rate. (c) What does the comparison tell you about how the plates have moved over time?
Part 3: Explaining the Ages of Crust (Problems 5-6)
The oldest large areas of ocean floor are about 180 million years old, and the oldest known continental rocks are about 4.0 billion years old. (a) How many times older is the oldest continental rock? (b) If deep-sea sediment builds up at 1.5 m per million years, predict the sediment thickness on 180-million-year-old ocean floor and on ocean floor that is 4.0 billion years old. (c) Use plate tectonics to explain the difference in rock ages.
A chain of volcanic islands formed as a plate moved over a fixed hot spot. The islands are 0, 1.8, 3.9 and 7.5 million years old at 0, 150, 330 and 640 km from the active volcano. (a) Find the plate speed from each older island. (b) Is the speed steady? (c) A GPS station on the youngest island moves at 86 mm/yr. Evaluate whether the past and current rates agree.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Analysis of Data
Rates and ages computed correctly with units, and patterns described with numbers
Correct method with one calculation or unit error
Evaluation of Evidence
Says whether each data set shows past or current movement and judges its strength with a reason
Evidence identified but not evaluated
Plate Tectonic Explanation
Explains the ages of crust with spreading, subduction or collisions, as the data require
Names plate tectonics without linking the process to the ages
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented and follow real patterns. Use 1 km per million years = 1 mm/yr. 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
Along a line of drill sites across an ocean basin, where would you expect to find the youngest oceanic crust?
Answer: A
New basalt forms where magma rises at the ridge axis, so the youngest crust is there. Choice C reverses the pattern: trenches are where the oldest ocean floor is subducted. Choice D ignores the drill-core data, which show age rising with distance from the ridge.
Question 2 of 20 · Multiple Choice
Basalt 90 km from a ridge formed at the ridge and has moved away from it at a steady 30 mm/yr. How old is the basalt?
Answer: C
30 mm/yr is 30 km per million years, so the age is 90 ÷ 30 = 3.0 million years. Choice D multiplies instead of dividing. Choice B divides the rate by the distance, and choice A uses twice the rate, as if the total spreading rate applied to one side.
Question 3 of 20 · Multiple Choice
Why is almost no oceanic crust older than about 200 million years?
Answer: B
Oceanic crust is dense, so when it reaches a trench it is subducted and recycled; only crust younger than its trip from ridge to trench survives. Choice A conflicts with evidence of much older marine sediments on land. Choice D is false: older rocks are dated routinely on the continents.
Question 4 of 20 · Multiple Choice
Magnetic stripes on the ocean floor form a mirror-image pattern on the two sides of a ridge. What does this evidence best support?
Answer: D
Each stripe records the field direction when that crust cooled, and matching stripes on both sides mean they formed together at the axis and then moved apart. Choice B contradicts the stripes themselves, which record reversals. Choice A cannot explain why the pattern is centered on the ridge.
Question 5 of 20 · Multiple Choice
Why can continental crust survive for billions of years when oceanic crust cannot?
Answer: A
Continental crust is buoyant compared with oceanic crust, so at a trench the oceanic plate sinks while the continent stays at the surface. Choice C contradicts GPS and rock-record evidence of continental motion. Choice D describes oceanic crust.
Question 6 of 20 · Multiple Choice
Across North America, crust is oldest in an interior core and younger toward the edges. Which explanation best fits plate tectonics?
Answer: B
Island arcs and other crust carried by moving plates collided with the old core at different times, adding younger belts outward. Choice A would remove crust but would not create younger rock at the edges. Choice D does not explain the steady outward decrease in age.
Question 7 of 20 · Multiple Choice
A reversal boundary is found 84 km from a ridge in crust that is 2.0 million years old. What is the rate at which the crust moved away from the ridge?
Answer: D
84 km ÷ 2.0 million years = 42 km per million years = 42 mm/yr. Choice A multiplies instead of dividing. Choice B is off by a factor of 10 in the unit conversion, and choice C halves the answer as if 42 mm/yr were the total rate.
Question 8 of 20 · Multiple Choice
Which kind of evidence measures the movement of plates happening today?
Answer: C
GPS stations measure how far they move from one year to the next, which is present-day motion. The other choices are records of past movement: stripes and basalt ages record when crust formed (choices A and B), and matching fossils (choice D) show that continents were once joined.
Question 9 of 20 · Multiple Choice
At an invented ridge, crust 100 km east of the axis is 5.0 million years old and crust 100 km west is 2.5 million years old. What do the data suggest?
Answer: A
West: 100 ÷ 2.5 = 40 mm/yr. East: 100 ÷ 5.0 = 20 mm/yr. Crust that reached 100 km in less time moved faster, so the west side is twice as fast. Choice B reads the older age as the faster rate, and choice D ignores the difference in ages.
Question 10 of 20 · Multiple Choice
Sediment on the ocean floor gets thicker with distance from a ridge. How does this support plate tectonics?
Answer: D
Sediment settles slowly and steadily, so its thickness acts as a clock: older crust has had more time to collect it. This agrees with the drill-core ages. Choice B has the source wrong: most deep-sea sediment settles from the water above.
Question 11 of 20 · Multiple Choice
An extinct volcanic island is 400 km from the hot spot that formed it and is 5.0 million years old. What was the average plate speed?
Answer: A
400 km ÷ 5.0 million years = 80 km per million years = 80 mm/yr. Choice B divides the age by the distance and misplaces the units, choice C multiplies instead of dividing, and choice D is off by a factor of 10.
Question 12 of 20 · Multiple Choice
A lab reports a basalt sample from the middle of the Pacific Ocean floor that is 3.9 billion years old. How should a scientist evaluate this result?
Answer: C
One result that conflicts with thousands of consistent drill-core ages is more likely an error or a misidentified sample (for example, a piece of continental rock). Choice A ignores the evidence base, and choice D is false because basalt is dated by radioactive decay.
Question 13 of 20 · Multiple Choice
Two continents are now 3,000 km apart across an ocean that has opened at a total rate of 25 mm/yr. About how long ago were they joined?
Answer: B
3,000 km ÷ 25 km per million years = 120 million years. Choice C uses half the rate (12.5 mm/yr), and choice A uses twice the rate. Choice D multiplies, giving an age older than Earth.
Question 14 of 20 · Multiple Choice
Which observation would most weaken the plate tectonic explanation of seafloor ages?
Answer: D
Plate spreading predicts that age increases with distance from the ridge, so equal ages at the ridge and far from it would contradict the model. Choices A, B and C are what plate tectonics predicts, so they support it.
Question 15 of 20 · Short Answer
Invented basalt ages on one side of a ridge are 1.5, 3.0 and 4.5 million years at 54, 108 and 162 km. Find the rate and predict the age of basalt 252 km from the ridge on the same side.
Each 54 km adds 1.5 million years, so the rate is 54 ÷ 1.5 = 36 mm/yr. At 252 km, the age is 252 ÷ 36 = 7.0 million years, if the rate stayed steady.
Question 16 of 20 · Short Answer
A student claims: "The ocean floor is young because the oceans themselves formed only about 200 million years ago." Evaluate the claim with evidence.
The claim is not supported. The pattern of ages (youngest at ridges, older with distance, mirror-image magnetic stripes) shows the ocean floor is continuously made at ridges and destroyed at trenches. Marine sediment and fossils in continental rocks show that oceans existed long before 200 million years ago. The ocean floor is young because it is recycled, not because the oceans are new.
Question 17 of 20 · Short Answer
A GPS station's distance from a marker on a neighboring plate is 0, 12, 23, 37 and 48 mm at years 0, 1, 2, 3 and 4. Find the rate of motion and say whether this is evidence of past or current movement.
The best-fit slope is about 12 mm/yr (48 mm in 4 years). This is evidence of current movement, because it was measured directly over the last few years.
Question 18 of 20 · Short Answer
Explain, using plate tectonics, why the oldest crust of North America lies in its interior while its edges are younger.
The interior is an ancient core that has survived because continental crust resists subduction. Over time, moving plates carried island arcs and other blocks of crust into the edges of the continent, where collisions welded them on, so each added belt is younger than the core it attached to.
Question 19 of 20 · Short Answer
Deep-sea sediment builds up at about 3 m per million years. Predict its thickness on 150-million-year-old ocean floor and on ocean floor that would be 4.0 billion years old if the ocean floor never moved. Which prediction fits observations of a few hundred meters?
150 × 3 = 450 m; 4,000 × 3 = 12,000 m (12 km). Observed thicknesses of a few hundred meters fit the young ocean floor that plate tectonics predicts, not a fixed ancient one.
Question 20 of 20 · Short Answer
GPS stations on opposite sides of a ridge separate at 64 mm/yr. Magnetic stripes show crust 2.0 million years old 62 km from the ridge on each side. Compare the two rates and evaluate what they show.
Stripes: 62 ÷ 2.0 = 31 mm/yr per side, so 62 mm/yr in total. GPS: 64 mm/yr. They differ by about 3%, so the spreading measured today matches the average rate of the last 2 million years: past and current movement agree.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-ESS1-5 mean?
HS-ESS1-5 asks students to weigh the evidence that Earth's crust has moved and is still moving, and to use plate tectonics to explain how old different crustal rocks are. The two key patterns are ocean floor that gets older away from mid-ocean ridges and continents with ancient cores. The code stands for High School, Earth and Space Science, core idea 1 (Earth's Place in the Universe), performance expectation 5.
Is HS-ESS1-5 part of Earth science?
Yes. It is usually taught in a high school Earth and Space Science course, often in a plate tectonics or Earth history unit. Some integrated science courses place it next to HS-ESS2-1, which models how Earth's processes build continents and ocean floor.
Does HS-ESS1-5 have an assessment boundary?
No. NGSS lists no Assessment Boundary for HS-ESS1-5. The Clarification Statement sets the focus instead: using plate tectonics to explain the ages of crustal rocks, with seafloor ages and the ages of North American crust as its two examples.
Why is oceanic crust younger than continental crust?
Oceanic crust is recycled and continental crust is not. It forms at mid-ocean ridges and, being dense, sinks back into the mantle at subduction zones, so nearly all of it is younger than about 200 million years. Continental crust is lighter and floats, which lets some of it last about 4 billion years.
How do magnetic stripes show seafloor spreading?
They record the direction of Earth's magnetic field when each strip of crust cooled. Because the field reverses from time to time, the ocean floor carries bands of normal and reversed magnetism, and the bands match on the two sides of a ridge. Dividing a band's distance from the ridge by the age of its reversal gives the spreading rate.
How do scientists know the ages of seafloor rocks?
They use several independent methods that agree. Basalt from drill cores is dated with radioactive decay, microfossils in the sediment just above the basalt give its age range, and the magnetic stripe pattern can be matched to the dated record of field reversals.
What evidence shows plates are moving today?
GPS is the most direct evidence. Stations fixed to bedrock record their position many times a day, and over a few years they show plates moving a few centimeters per year. Earthquakes along plate boundaries are further evidence of ongoing motion.
What misconceptions do students have about plate tectonics and rock ages?
A frequent one is that the oceans are young, rather than the ocean floor. Other misconceptions are that plates move too slowly to measure, that the oldest ocean floor must be next to a ridge, and that one surprising data point overturns a well-supported theory. Asking students to compare several kinds of evidence addresses all four.
Can HS-ESS1-5 be taught without lab equipment?
Yes. The practice is evaluating evidence, so data tables, graphs and maps do most of the work. A paper model of magnetic stripes, public seafloor age maps and GPS velocity data from geoscience agencies give students real patterns to analyze at little or no cost.
How does HS-ESS1-5 connect to other standards?
It builds on MS-ESS2-3, where students use fossils, rocks and seafloor structures as evidence of past plate motion. At the high school level it pairs with HS-ESS2-1 and HS-ESS2-3 on the processes that move plates, and it leads to HS-ESS3-1, where students connect plate boundaries to natural hazards and resources.
07
Related Standards
5 standards
These standards connect to HS-ESS1-5: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-ESS2-3Prerequisite
Analyze fossil, rock, continent and seafloor data as evidence of past plate motions
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
