HS-ESS2-3NGSS*ScienceEarth and Space ScienceGrades 9-12
HS-ESS2-3: Modeling Earth's Interior and Mantle Convection from Evidence
In plain English: HS-ESS2-3 is the NGSS high school performance expectation that asks students to develop a model of Earth's interior, based on evidence from seismic waves, the magnetic field and high-pressure experiments, that shows how thermal convection cycles matter through the mantle and core. Students build a layered density model and a convection model linked to plate tectonics. It is usually taught in Earth and Space Science.
Develop a model based on evidence of Earth's interior to describe the cycling of matter by thermal convection.
Clarification Statement: Emphasis is on both a one-dimensional model of Earth, with radial layers determined by density, and a three-dimensional model, which is controlled by mantle convection and the resulting plate tectonics. Examples of evidence include maps of Earth's three-dimensional structure obtained from seismic waves, records of the rate of change of Earth's magnetic field (as constraints on convection in the outer core), and identification of the composition of Earth's layers from high-pressure laboratory experiments.
Next Generation Science Standards · Disciplinary Core Idea: Earth's Systems · Official standard
Students build two linked models of Earth's interior and support each one with evidence. The one-dimensional model is a set of radial layers ordered by density: crust, mantle, liquid outer core and solid inner core. The three-dimensional model shows the mantle as hot, solid rock that flows very slowly in convection currents: hot rock rises because it is less dense, cold ocean plates sink at trenches, and the plates on the surface are the top of this cycle. The liquid outer core also convects, much faster, and its flow makes Earth's magnetic field. Students use Earth's average density, seismic wave data, travel-time maps, magnetic field records and results from high-pressure experiments.
The NGSS Clarification Statement says: "Emphasis is on both a one-dimensional model of Earth, with radial layers determined by density, and a three-dimensional model, which is controlled by mantle convection and the resulting plate tectonics. Examples of evidence include maps of Earth's three-dimensional structure obtained from seismic waves, records of the rate of change of Earth's magnetic field (as constraints on convection in the outer core), and identification of the composition of Earth's layers from high-pressure laboratory experiments." There is no official Assessment Boundary for this performance expectation. Physical values on this page are rounded standard values (Earth's mass 5.97 × 1024 kg, radius 6,371 km, core radius 3,480 km); station and experiment data are invented or rounded for teaching and labeled that way. Students do the practice of developing a model: they build it from data, test it with calculations and name its limits.
Learning Objectives
By the end of this lesson, students will be able to:
Use Earth's average density and a layered model to show that the interior must be much denser than surface rock
Interpret seismic evidence (shadow zones and travel-time differences) to identify liquid and solid layers and hot and cold regions of the mantle
Use records of magnetic field change and high-pressure experiment results as evidence about the composition and motion of the core
Develop a model that shows how thermal convection cycles matter between Earth's surface and deep interior, and connect it to plate motion
Prior Knowledge Required
Students should already be comfortable with:
The cycling of Earth's materials and the energy that drives it MS-ESS2-1
Density = mass ÷ volume, and the volume of a sphere, V = (4/3)πr³
How heating changes particle motion and the density of a material MS-PS1-4
Evidence for plate motion from rocks, fossils and sea-floor features MS-ESS2-3
Hold up a closed box with an unknown object inside and let a few students shake and weigh it.
Warm-Up Prompt
"The deepest hole ever drilled went about 12 km down, less than 0.2% of the way to Earth's center. List three ways you could find out what is inside Earth without going there. For each, say what you would measure."
Collect ideas (weigh it, send vibrations through it, test materials under pressure, watch its magnetism). Tell students that geoscientists use all four, and today they will use each one as evidence for a model.
Direct Instruction15-20 minutes
Two models, many kinds of evidence. Earth's mass (from gravity) and size give its average density. Seismic waves from earthquakes travel through the interior: P waves pass through solids and liquids, and S waves pass only through solids, and their speed depends on the rock's temperature and composition. Maps of travel times build three-dimensional pictures of the mantle: waves slow down in hotter rock and speed up in colder rock. Changes in the magnetic field over years and decades show fast flow of liquid iron in the outer core. High-pressure laboratory experiments squeeze iron and mantle minerals to deep-Earth pressures, measure their densities, and show, for example, that the mineral olivine changes to denser crystal structures at the pressures found near 410 km and 660 km deep, the depths where seismic speeds jump. Use Diagrams 1 and 2, then the examples.
1D model: Earth's average density
Earth's mass is 5.97 × 1024 kg and its radius is 6,371 km. Crust rocks have densities of 2.7-3.0 g/cm³.
Result: V = (4/3)π(6.371 × 106 m)³ = 1.083 × 1021 m³, so the average density is 5.97 × 1024 ÷ 1.083 × 1021 ≈ 5,510 kg/m³ = 5.51 g/cm³, about twice that of crust rock. The interior must be much denser than the surface.
1D model: a two-layer Earth
Model Earth as a mantle with an average density of 4.5 g/cm³ around a core of radius 3,480 km. The core fills (3,480 ÷ 6,371)³ = 0.163 of Earth's volume.
Result: 5.51 = 0.163 × (core density) + 0.837 × 4.5, so the core density is (5.51 - 3.77) ÷ 0.163 ≈ 10.7 g/cm³, far denser than rock and close to iron squeezed at high pressure.
Seismic evidence: the S-wave shadow
Direct S waves from an earthquake are not recorded more than about 104° around Earth from it. A simple model draws the ray that just misses the core as a straight line (chord).
Result: A straight chord spanning 104° comes within 6,371 × cos 52° ≈ 3,920 km of the center. The real core radius is 3,480 km: the straight-line model overestimates it, because real rays curve as wave speed changes with depth. The shadow itself shows the outer core is liquid, since S waves cannot pass through liquid.
Seismic evidence: a travel-time map
Invented data: P waves on two 1,000 km paths through the lower mantle are expected to take 100.0 s at 10.0 km/s. One path takes 102.0 s, and the other 98.0 s.
Result: Average speeds: 1,000 ÷ 102.0 ≈ 9.80 km/s (2% slow) and 1,000 ÷ 98.0 ≈ 10.20 km/s (2% fast). The slow region is hotter rock, likely rising; the fast region is colder rock, likely a sinking plate.
Magnetic evidence: flow in the outer core
A feature of the magnetic field at the top of the core drifts west by about 0.2° of longitude per year. The circumference at the core surface is 2π × 3,480 km ≈ 21,900 km.
Result: Speed ≈ (0.2 ÷ 360) × 21,865 km ≈ 12 km/yr, hundreds of thousands of times faster than mantle flow of a few cm/yr. Only a liquid can flow that fast, so the outer core is convecting liquid metal.
After each example ask: "Which model does this evidence support, the layered one or the convecting one, and what would change in the model if the numbers were different?"
Guided Practice15 minutes
Pairs analyze which seismic stations record direct P and S waves from one earthquake. The pattern is rounded from real observations; distances are measured as angles around Earth from the earthquake.
Guided practice data: direct waves recorded at stations
Distance from earthquake
Direct P recorded?
Direct S recorded?
30°
yes
yes
60°
yes
yes
90°
yes
yes
110°
no
no
130°
no
no
150°
yes
no
170°
yes
no
Sketch Earth and mark each station. Shade the distances where no direct S wave arrives.
S waves need a solid to travel through. Which layer stops them, and what state is it in?
P waves reach stations at 150° and 170° but not at 110° or 130°. Draw how bending (refraction) at the core boundary could leave a gap.
Add the liquid outer core to the class model, and write the evidence next to it.
Independent Practice15 minutes
Each student tests a three-layer model of Earth by computing the mass of each layer and comparing the total with Earth's measured mass of 5.97 × 1024 kg. Densities are rounded averages.
Three-layer model (rounded averages)
Layer
From radius (km)
To radius (km)
Average density (g/cm³)
Crust and mantle
3,480
6,371
4.5
Outer core
1,220
3,480
10.9
Inner core
0
1,220
12.9
Students use V = (4/3)π(router³ - rinner³) for each shell, convert to kilograms, and find the percent difference between the model total and the measured mass. Then they name one improvement to the model and the evidence that would support it.
Closure5 minutes
Exit ticket: "Draw one loop that follows a piece of ocean plate from a spreading ridge, down a trench, through the mantle and back up. Label where it is hot and less dense and where it is cold and denser, and name one piece of evidence for the sinking part."
Differentiation Strategies
For Struggling Students
Give a blank cross-section with the layer boundaries already drawn to scale, and a word bank of layer names and states
Provide an evidence card for each data type (density, seismic, magnetic, laboratory) with one sentence on what it measures
Do the density and volume calculations in scientific notation with a calculator template before the full three-layer model
For Advanced Students
Ask students to explain why the straight-ray estimate of the core radius is too large, using a sketch of a curved ray
Have students estimate how long one loop of a mantle convection cell takes, using a cell size and a flow speed they justify
Ask students to compare the pressure and temperature at the core boundary with what laboratory presses can reach, and explain why experiments can test the model
Assessment Guidance
What to Look For
Check that students treat the mantle as solid rock that flows slowly, not as a sea of magma, and that the evidence for this (S waves pass through the mantle) appears in their models. Look for density used correctly (mass ÷ volume) and for volume fractions of shells computed with cubes of radii. Listen for the link between the two models: denser layers sit deeper, and within the mantle, temperature differences change density and drive convection.
02
Classroom Activities
3 Activities
1
Density Column: A One-Dimensional Earth
20 minGroups of 3-4
Groups measure the density of four household liquids, predict their order, and pour them into one clear cup to build a layered column. They compare the column with the layered model of Earth and list what the model gets right and wrong.
Procedure
Measure 50 mL of each liquid in a graduated cylinder and weigh it on the scale (subtract the cylinder's mass).
Compute each density and predict the order from bottom to top.
Pour the liquids slowly down the side of the cup in order from densest to least dense, then drop in a small steel nut and a plastic bead and see where each settles.
Safety: wear goggles, do not taste anything, and wipe up oil and soap spills at once because they make floors slippery.
Sample Data (invented)
Mass of 50 mL: honey 71.0 g, dish soap 53.0 g, water 50.0 g, vegetable oil 46.0 g.
Discussion Questions
Compute the four densities. Did the layers form in the order you predicted?
Which liquid layer plays the part of the core, and which the crust? What does the steel nut stand for?
Name two ways Earth is unlike the column (for example, most of Earth is solid, and pressure makes deep layers denser).
Modification for Distance Learning
Students build the column at home in a clear glass with liquids they have, or they compute the densities from the sample data and draw the column.
2
Convection Tank: Modeling the Moving Mantle
25 minGroups of 3-4
Groups set a clear tank of room-temperature water on two stacks of blocks, with a mug of hot tap water under one end and a mug of ice water under the other. Drops of food coloring placed on the bottom show how warm water rises, spreads, cools and sinks.
Procedure
Fill the tank about 10 cm deep and let the water settle for 2 minutes.
Slide the mugs under the ends. With a dropper, release one drop of food coloring on the bottom above each mug.
Time how long the colored water above the hot mug takes to rise 8 cm, and sketch the flow every 30 seconds.
Safety: use hot tap water only, never boiling water, a stove or an open flame. Wear goggles, carry the tank empty, and wipe spills at once.
Sample Data (invented)
The colored water above the hot mug rose 8 cm in 20 s, spread along the surface, and sank above the ice-water mug about 60 s after the drop was released.
Discussion Questions
Find the rising speed in cm/s. Real mantle rock moves a few centimeters per year. About how many times faster is the model?
Which part of the tank stands for the hot core boundary, a rising plume, and a cold sinking plate?
The mantle is solid rock, not water. Why can a solid still convect, and why does it take so long?
Modification for Distance Learning
Students watch a recorded demonstration or run the model in a clear glass dish at home, then annotate a screenshot with arrows for rising and sinking flow.
3
Evidence Stations: Building the 3D Model
25 minGroups of 3-4
Four stations each hold one kind of evidence about Earth's interior. At each station, groups analyze the data, add one feature to a large class cross-section, and write the evidence on a sticky note next to it. Groups rotate every 6 minutes.
Station Data (invented or rounded)
Station 1, seismic travel-time map: wave-speed differences from average below an ocean trench are +1.5%, +1.2% and +0.8% at 300, 900 and 1,500 km deep; below a hot-spot volcano they are -2.0%, -1.2% and -1.0% at 300, 1,500 and 2,700 km deep.
Station 2, magnetic records: a magnetic feature at the top of the core sat at 20°E, 15°E and 10°E longitude in 1950, 1970 and 1990.
Station 3, high-pressure experiments (rounded values): pure liquid iron at the pressure and temperature of the top of the outer core has a density of about 10.9 g/cm³; seismic models give 9.9 g/cm³ for the outer core there.
Station 4, plates and slabs: an ocean plate has sunk at a trench at 6 cm/yr for 40 million years, and the travel-time map shows its cold slab reaching 1,200 km deep.
Discussion Questions
At Station 1, which column shows a cold sinking slab and which a hot rising plume? Explain using the signs of the numbers.
At Station 2, find the drift rate in degrees per year and the flow speed at the core surface.
At Station 3, by what percent is the outer core less dense than pure iron, and what does that suggest about its composition?
At Station 4, how much plate has gone down the trench, and why is that length greater than the slab's depth?
Modification for Distance Learning
Post each station as a slide and give each group a shared cross-section drawing to annotate during breakout rooms.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Earth's Interior, Layers and Convection
A cross-section with radii drawn to scale. The right half is the one-dimensional model: layers ordered by density, with their states and rounded densities. The left half is the three-dimensional model: slow convection loops in the solid mantle between the core boundary and the plates, which are too thin to draw. The dashed circle marks 660 km deep.
Diagram 2: Density Against Depth
Rounded densities from a standard reference Earth model, drawn to scale. Density rises with depth inside each layer because of pressure, and it jumps where composition or state changes, most of all at the core boundary 2,890 km down. Most of the mantle is below the whole-Earth average, so the core must be well above it.
04
Homework Assignment
~30 min
HS-ESS2-3 Homework: Testing Models of Earth's Interior
Directions: Data are rounded standard values or invented for practice. Use Earth's radius 6,371 km, core radius 3,480 km and average density 5.51 g/cm³ where needed. Show each calculation, and for every problem say which model (layered or convecting) the evidence supports.
Part 1: The Layered Model (Problems 1-2)
In a two-layer model, the core fills 0.163 of Earth's volume. (a) Find the core density if the mantle averages 4.3 g/cm³. (b) Repeat for a mantle average of 4.7 g/cm³. (c) Laboratory data suggest iron alloys at core pressures have densities of about 10-13 g/cm³. Do both mantle guesses give a believable core? What does this tell you about how sensitive the model is?
Invented station records for one earthquake: direct P and direct S both arrive at 50°, 80° and 100°; neither arrives at 120°; P arrives but S does not at 145° and 160°. (a) What do the records show about the state of the outer core? (b) Why can P waves reach 145° but not 120°? (c) Draw a cross-section model that explains the whole pattern.
Part 2: Seismic and Magnetic Evidence (Problems 3-4)
Two P waves travel 1,500 km through the lower mantle, where the expected speed is 12.0 km/s. (a) Find the expected travel time. (b) The waves arrive after 127.5 s and 123.0 s. Find each average speed and its percent difference from 12.0 km/s. (c) Which path crosses hotter rock? Is that rock more likely rising or sinking, and why?
A magnetic feature at the top of the core drifts 0.3° of longitude per year. (a) Find its speed in km/yr, using a core-surface circumference of 21,865 km. (b) How many times faster is this than a plate moving 5 cm/yr? (c) Explain why this evidence supports a convecting liquid outer core.
Part 3: Laboratory Evidence and the Convection Model (Problems 5-6)
Rounded high-pressure results: pure iron at inner-core pressure and temperature would have a density of about 13.4 g/cm³, while seismic models give the inner core about 12.9 g/cm³. (a) By what percent is the inner core less dense than pure iron? (b) The outer core is about 9% less dense than pure liquid iron at its own pressure and temperature. Which part of the core contains a larger share of lighter elements, and how do you know? (c) Why do geoscientists need experiments as well as seismic data to answer this?
Develop a model of one mantle convection cell. (a) Draw a labeled cross-section that shows where rock is hot and rising, cold and sinking, and moving sideways under the plates. (b) If one full loop is 12,000 km long and rock moves 4 cm/yr on average, how long does one loop take? (c) Name the evidence for the sinking part and for the rising part.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Correct densities, speeds, times and percent differences with units
Correct method with one arithmetic or unit error
Model
Cross-sections show layers by density and convection in the solid mantle, with every feature labeled
Model has layers or convection but not both, or labels are missing
Evidence and Reasoning
Each claim names the evidence (seismic, magnetic, laboratory or density) and explains how it supports the model
Evidence named but not connected to the model
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Values are rounded standard values or invented data. Use density = mass ÷ volume and time = distance ÷ speed. 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
In the one-dimensional model of Earth, what mainly sets the order of the layers from the center outward?
Answer: A
As Earth formed and heated, denser material such as iron sank toward the center and less dense rock rose. Choice C is wrong because temperature rises with depth. Choice B confuses interior layers with rock layers laid down at the surface.
Question 2 of 20 · Multiple Choice
Earth's average density is about 5.5 g/cm³, while crust rocks are about 2.7-3.0 g/cm³. What does this comparison show?
Answer: C
If the outer layer is lighter than the average, something deeper must be heavier to bring the average up. Choice D would make the average equal to the crust value. Choice B would make the average lower than the crust value, not higher.
Question 3 of 20 · Multiple Choice
On an invented rocky planet, seismometers record direct S waves at every distance from every quake. What does this suggest about the planet?
Answer: B
S waves cannot travel through liquid, so a large liquid layer would block them and leave a shadow zone. Recording them everywhere suggests no such layer. Choices A and C both describe a liquid layer the S waves could not cross. Choice D goes too far: a solid core would still let S waves pass.
Question 4 of 20 · Multiple Choice
A P wave travels 2,400 km at an average speed of 12 km/s. How long does the trip take?
Answer: D
Time = distance ÷ speed = 2,400 ÷ 12 = 200 s. Choice A multiplies instead of dividing. Choice C divides speed by distance. Choice B slips a factor of 10.
Question 5 of 20 · Multiple Choice
A travel-time map shows that seismic waves pass through one region of the mantle more slowly than average. What is the best interpretation?
Answer: C
Waves slow down in hotter rock, and hot rock is less dense, so it tends to rise. Choice A matches fast regions. Choice B goes too far: S waves still cross the mantle, so it is mostly solid.
Question 6 of 20 · Multiple Choice
A magnetic feature at the top of the core drifts 0.15° of longitude per year. The circumference there is about 21,865 km. About how fast is the flow?
Answer: A
Speed = (0.15 ÷ 360) × 21,865 ≈ 9.1 km/yr. Choice B multiplies the circumference by 0.15 without dividing by 360. Choices C and D are off by a factor of 10.
Question 7 of 20 · Multiple Choice
Why does hot rock deep in the mantle rise?
Answer: B
Heating makes rock expand, so the same mass takes up more volume and its density drops; the denser rock around it sinks and pushes it up. Choice A is wrong because the mantle stays solid and flows slowly. Choices C and D name forces that do not drive mantle flow.
Question 8 of 20 · Multiple Choice
Which is an example of evidence from high-pressure laboratory experiments about Earth's interior?
Answer: C
Experiments recreate deep-Earth pressures and measure the properties of materials, such as the density of iron. Choice A is seismic evidence, choice B is magnetic evidence, and choice D is sea-floor evidence for plate motion.
Question 9 of 20 · Multiple Choice
Seismic models say the outer core is several percent less dense than pure iron would be at the same pressure and temperature. What is the best conclusion?
Answer: B
An iron-rich liquid with some lighter elements (such as oxygen, sulfur or silicon) would be a little less dense than pure iron. Choice A is ruled out because rock is far less dense than the core. Choice D contradicts the S-wave shadow evidence.
Question 10 of 20 · Multiple Choice
A cold slab of ocean plate sinks 2,000 km through the mantle at an average of 2 cm/yr. About how long does that take?
Answer: C
2,000 km = 2 × 108 cm, and 2 × 108 ÷ 2 = 108 years, or 100 million years. Choices A, B and D are each off by factors of 10 from a slip in the unit conversion.
Question 11 of 20 · Multiple Choice
In the three-dimensional convection model, which feature is the cold, sinking part of the cycle?
Answer: D
Old ocean plate is cold and dense, so it sinks back into the mantle at trenches. Choices A and B are places where hot material rises. Choice C is not part of mantle convection.
Question 12 of 20 · Multiple Choice
A two-layer model has a core that fills 0.16 of the volume with density 12.0 g/cm³ and a mantle with density 4.4 g/cm³. What average density does the model give?
Answer: B
Weight each density by its share of the volume: 0.16 × 12.0 + 0.84 × 4.4 = 1.92 + 3.696 ≈ 5.62 g/cm³, a little above the measured 5.51, so this core density is slightly too high. Choice A is a plain average that ignores volume. Choice C swaps the two shares. Choice D adds the densities.
Question 13 of 20 · Multiple Choice
What does the three-dimensional model of Earth add that the one-dimensional model leaves out?
Answer: C
The one-dimensional model assumes each depth is the same everywhere. The three-dimensional model adds sideways differences, hot rising and cold sinking regions, which drive plate motion. Choices A, B and D are already in the layered model.
Question 14 of 20 · Multiple Choice
In a high-pressure experiment, a mineral sample has a mass of 8.8 g and a volume of 2.0 cm³. Which part of Earth has a density like this?
Answer: A
Density = 8.8 ÷ 2.0 = 4.4 g/cm³, which matches the top of the lower mantle. Choice B multiplies mass by volume. Choice C halves the correct value. Choice D divides volume by mass.
Question 15 of 20 · Short Answer
In a two-layer model, the core fills 0.163 of Earth's volume and the mantle averages 4.6 g/cm³. Earth's average density is 5.51 g/cm³. Find the core density and say whether it fits an iron-rich core.
5.51 = 0.163 × ρ + 0.837 × 4.6, so ρ = (5.51 - 3.85) ÷ 0.163 ≈ 10.2 g/cm³. That is far denser than rock and close to the density of compressed iron, so the model supports an iron-rich core.
Question 16 of 20 · Short Answer
A P wave crosses 1,200 km of upper mantle where the expected speed is 8.0 km/s. It arrives after 153 s. Find the expected time, the measured average speed and the percent difference, and interpret the result.
Expected time = 1,200 ÷ 8.0 = 150 s. Measured speed = 1,200 ÷ 153 ≈ 7.84 km/s, about 2% slower than expected. The wave crossed hotter rock than average, which is less dense and likely rising, for example above a plume.
Question 17 of 20 · Short Answer
Develop a model in words or a labeled sketch: describe how matter from an ocean plate cycles through the mantle by thermal convection, and give one piece of evidence for two different steps.
A strong answer: new plate forms where hot mantle rises and melts at a ridge; the plate cools and becomes denser as it moves away; at a trench the cold, dense plate sinks; it heats slowly deep in the mantle, and hot, less dense rock rises elsewhere to close the loop. Evidence: fast (cold) slabs on travel-time maps below trenches for sinking; slow (hot) columns below hot-spot volcanoes for rising; sea-floor ages for spreading. Rubric: 1 point for a closed loop, 1 for density and temperature at each step, 1 for two correct pieces of evidence.
Question 18 of 20 · Short Answer
Magnetic observatories show Earth's field changing noticeably within a few decades. Explain why this is evidence about the outer core and not the mantle. Support your answer with a comparison of how far each moves in 50 years.
In 50 years, mantle rock moving about 3 cm/yr moves only 1.5 m, far too little to change the field noticeably. Flow at the core surface of about 12 km/yr moves roughly 600 km in 50 years. Fast changes in the field therefore come from the fast-moving liquid iron of the outer core.
Question 19 of 20 · Short Answer
A student says: "The mantle must be liquid magma, because it convects." Use seismic evidence to evaluate the claim.
The claim is not supported. S waves, which cannot travel through liquids, pass through the whole mantle, so the mantle is solid. Solid rock that is hot and under great pressure can still flow very slowly, a few centimeters per year, which is enough for convection over millions of years. Only small pockets melt, for example below ridges and volcanoes.
Question 20 of 20 · Short Answer
Earth's core fills about 16% of Earth's volume but holds about 32% of its mass. Use these numbers to estimate the core's average density, and explain what the result tells you.
The core's density divided by Earth's average density equals its mass share divided by its volume share: 0.32 ÷ 0.16 = 2. So the core is about twice as dense as the average: 2 × 5.51 ≈ 11 g/cm³. That is far denser than any rock and fits a core made mostly of iron.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-ESS2-3 mean?
HS-ESS2-3 asks students to develop a model of Earth's interior, based on evidence, that describes how thermal convection cycles matter. Students build a layered model ordered by density and a model of convection in the mantle and core, and they support both with seismic, magnetic and laboratory evidence. The code means High School, Earth and Space Science, core idea 2 (Earth's Systems), performance expectation 3.
Is HS-ESS2-3 taught in Earth science or physics?
It is usually taught in a high school Earth and Space Science course, often in a unit on plate tectonics. It uses physical science ideas (density, heat transfer, waves), so it can also connect to Physics or Chemistry.
Does HS-ESS2-3 have an assessment boundary?
No. NGSS lists no Assessment Boundary for HS-ESS2-3. The Clarification Statement sets the emphasis: a one-dimensional model with layers set by density and a three-dimensional model controlled by mantle convection and plate tectonics, supported by seismic, magnetic and laboratory evidence.
How do scientists know what is inside Earth?
Mostly from indirect evidence, because no one can drill more than a small fraction of the way down. Earth's mass and size give its average density; seismic waves reveal layers, states and temperature differences; changes in the magnetic field show flow in the liquid core; and high-pressure experiments show how iron and minerals behave at deep-Earth conditions.
Is the mantle liquid?
No. The mantle is solid rock, as shown by S waves passing through it. Because it is hot and under high pressure, the rock flows very slowly, a few centimeters per year, like an extremely stiff putty. Only small amounts melt, mainly under ridges and volcanoes. The liquid layer is the outer core.
What is the difference between the 1D and 3D models of Earth?
The one-dimensional model describes how properties change with depth only: layers stacked by density. The three-dimensional model adds differences from place to place at the same depth, such as cold sinking slabs and hot rising plumes, which come from mantle convection and drive plate tectonics.
What drives mantle convection?
Heat from Earth's interior, from the planet's formation and from radioactive decay. Rock heated from below and within expands, becomes less dense and rises; rock cooled near the surface, especially old ocean plate, becomes denser and sinks. The plates are the cold top layer of this cycle.
How does Earth's magnetic field give evidence about the core?
The field is made by flowing liquid iron in the outer core. Records from observatories and old ship logs show the field changing over years and decades, and features drifting at rates that imply flow of kilometers per year. Such fast change needs a convecting liquid, which constrains models of the outer core.
What do high-pressure experiments show about Earth's layers?
Presses such as diamond-anvil cells squeeze tiny samples to the pressures of the mantle and core. They show that mantle minerals change to denser crystal structures at depths where seismic speeds jump, and they measure the density of iron at core pressures so it can be compared with the core densities found from seismic waves.
What comes after HS-ESS2-3?
HS-ESS1-5 evaluates evidence for past and present plate motions, and HS-ESS2-1 models how the internal processes powered by convection, together with surface processes, shape continents and sea floors. HS-ESS3-1 connects plate-driven hazards such as earthquakes and volcanoes to human activity.
07
Related Standards
5 standards
These standards connect to HS-ESS2-3: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-ESS2-1Prerequisite
Model the cycling of Earth's materials and the flow of energy that drives it
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.
