HS-ESS1-6NGSS*ScienceEarth and Space ScienceGrades 9-12
HS-ESS1-6: Reconstructing Earth's Formation and Early History
In plain English: HS-ESS1-6 is the NGSS high school performance expectation that asks students to use evidence from ancient Earth materials, meteorites and other planetary surfaces to construct an account of Earth's formation and early history. Students use radiometric ages, planet compositions and crater records to show Earth formed with the solar system about 4.6 billion years ago. It is usually taught in Earth and Space Science.
Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth's formation and early history.
Clarification Statement: Emphasis is on using available evidence within the solar system to reconstruct the early history of Earth, which formed along with the rest of the solar system 4.6 billion years ago. Examples of evidence include the absolute ages of ancient materials (obtained by radiometric dating of meteorites, moon rocks, and Earth's oldest minerals), the sizes and compositions of solar system objects, and the impact cratering record of planetary surfaces.
Next Generation Science Standards · Disciplinary Core Idea: Earth's Place in the Universe · Official standard
Students act like planetary scientists who cannot watch Earth form but can read the evidence it left behind. They use radiometric ages of meteorites, Moon rocks and Earth's oldest minerals, the sizes and densities of solar system objects, and the cratering record of planetary surfaces to build an account of how Earth formed and what its first few hundred million years were like. Along the way they explain why Earth's own surface keeps so little of that record, so much of the evidence comes from elsewhere in the solar system.
The NGSS Clarification Statement says: "Emphasis is on using available evidence within the solar system to reconstruct the early history of Earth, which formed along with the rest of the solar system 4.6 billion years ago. Examples of evidence include the absolute ages of ancient materials (obtained by radiometric dating of meteorites, moon rocks, and Earth's oldest minerals), the sizes and compositions of solar system objects, and the impact cratering record of planetary surfaces." NGSS lists no Assessment Boundary for HS-ESS1-6, so this lesson stays with evidence from within the solar system. Published ages and planet data are rounded standard values: U-235 half-life 0.704 billion years, U-238 half-life 4.47 billion years, K-40 half-life 1.25 billion years. Dating problems assume a closed sample with no daughter atoms at the start. Crater counts and class data are invented and labeled as invented.
Learning Objectives
By the end of this lesson, students will be able to:
Use half-lives and parent-daughter ratios to calculate the radiometric ages of meteorites, Moon rocks and Earth minerals
Explain why meteorites and the Moon preserve older records than Earth's surface, using plate tectonics and erosion
Use crater densities to rank the relative ages of planetary surfaces and explain how dated samples calibrate them
Use the sizes, masses and densities of solar system objects as evidence of how Earth formed and separated into layers
Construct a written account of Earth's formation and early history that cites at least three independent lines of evidence
Prior Knowledge Required
Students should already be comfortable with:
How rock strata and the geologic time scale organize Earth's 4.6-billion-year history MS-ESS1-4
Scale properties of objects in the solar system, such as size and distance MS-ESS1-3
Atoms, isotopes and the idea that some nuclei are unstable and decay
Density as mass divided by volume, and the volume of a sphere, V = 4/3 πr³
Show a photo of the Moon's heavily cratered highlands beside a photo of a green, farmed landscape on Earth.
Warm-Up Prompt
"The Earth and the Moon sit in the same part of space and have been hit by space rocks for billions of years. Why does the Moon look battered while Earth's surface shows almost no craters? If you wanted to know what happened on Earth 4.5 billion years ago, where would you look for evidence?"
List students' answers (weather, oceans, plants, volcanoes, moving plates) and the places they would look (the Moon, meteorites, very old rocks). The lesson tests each of these sources.
Direct Instruction15-20 minutes
Three kinds of evidence.Absolute ages come from radioactive decay: a parent isotope such as uranium-235 turns into a daughter (lead-207) at a known rate. After each half-life, half of the remaining parent atoms have decayed, so the parent fraction is (1/2)n after n half-lives, and the daughter-to-parent ratio is 2n - 1. Sizes and compositions tell us how material sorted itself: dense, rocky planets formed near the Sun and giant planets rich in gas and ice formed farther out, and a planet whose average density is higher than its surface rocks must have a dense metal core. Crater records give relative ages: an older surface has been hit more times, so it carries more craters per unit area. Earth's surface is constantly recycled by plate tectonics, erosion and weathering, so meteorites and the Moon preserve records that Earth has erased. Use Diagram 2 for decay and Diagram 1 for the timeline.
Meteorites: dating the birth of the solar system
The oldest solid grains in a stony meteorite contain about 89 atoms of lead-207 for every atom of uranium-235 left (half-life 0.704 billion years).
Result: Daughter ÷ parent = 2n - 1, so 2n = 90 and n = log2 90 ≈ 6.49 half-lives. Age ≈ 6.49 × 0.704 ≈ 4.57 billion years: the age of the solar system.
Earth's oldest minerals: a zircon crystal
A zircon grain from Western Australia contains about 0.98 atoms of lead-206 for every atom of uranium-238 left (half-life 4.47 billion years).
Result: 2n = 1.98, so n ≈ 0.985 and the age ≈ 0.985 × 4.47 ≈ 4.4 billion years. Solid crust existed on Earth less than 200 million years after the solar system formed.
Other planetary surfaces: counting craters on the Moon
Invented counts: a 20,000 km² area of lunar highlands has 480 craters wider than 4 km, and a 20,000 km² area of dark mare has 60.
Result: Highlands: 24 craters per 1,000 km². Mare: 3 per 1,000 km², 8 times fewer. The highlands are older, which matches Apollo samples: highland rocks are older than about 4 billion years, and mare basalts are about 3.1-3.9 billion years old.
Sizes and compositions: what density reveals
Earth has mass 5.97 × 10²⁴ kg and radius 6,371 km. Jupiter has mass 1.90 × 10²⁷ kg and radius 69,911 km. Rocks at Earth's surface are about 2.7-3.0 g/cm³.
Result: Earth: 5.97 × 10²⁴ ÷ (4/3 π (6.371 × 10⁶)³) ≈ 5,510 kg/m³ = 5.51 g/cm³, about twice its surface rocks, so Earth has a dense iron core. Jupiter: about 1.33 g/cm³, a planet made mostly of hydrogen and helium.
Putting the evidence together
Oldest meteorite solids: 4.567 billion years. Oldest Earth zircon: about 4.4 billion years. Oldest Earth rock: about 4.0 billion years.
Result: Earth formed with the rest of the solar system about 4.6 billion years ago. Its first crust formed within about 170 million years (4.567 - 4.4), but almost none of it survives as rock: plate tectonics, erosion and early impacts recycled it.
After each example, ask: "Which body did this evidence come from, and why couldn't we get the same evidence from Earth's surface?" Stress that the conclusion is strong because independent methods (meteorite ages, Moon rock ages, zircons, crater counts and planet densities) fit one account.
Guided Practice15 minutes
Pairs date four invented samples from their parent fraction, then place them on Diagram 1 and compare them with the oldest known Earth materials.
Guided practice data: invented samples
Sample
Parent isotope (half-life)
Parent remaining
1: Moon highland rock
U-235 (0.704 billion years)
1.4%
2: Moon mare basalt
K-40 (1.25 billion years)
16%
3: Canadian gneiss
U-238 (4.47 billion years)
53.7%
4: Stony meteorite
U-238 (4.47 billion years)
49.3%
Find the number of half-lives with n = log2(100 ÷ percent remaining), then multiply by the half-life.
Expected ages: about 4.3, 3.3, 4.0 and 4.56 billion years.
Place each sample on the timeline in Diagram 1 and label the body it came from.
Explain why the meteorite is older than any Earth rock, and why the Moon still has rocks as old as Sample 1 when Earth does not.
Independent Practice10 minutes
Each student compares Venus and Mars with Earth using published values: Venus has mass 4.87 × 10²⁴ kg and radius 6,052 km; Mars has a heavily cratered southern hemisphere and much smoother northern lowlands. Students compute the density of Venus (about 5.24 g/cm³), then write a paragraph that uses both planets as evidence about how rocky planets like Earth formed and why the oldest planetary surfaces are found off Earth.
Closure5-10 minutes
Exit ticket: "A sample has 1/8 of its original parent atoms left, and the parent has a half-life of 1.3 billion years. How old is it, and could it be a piece of Earth's oldest crust?" (3 half-lives, 3.9 billion years; it is younger than Earth's oldest minerals and rocks, so it is not.) Return to the warm-up and ask which evidence sources the class used.
Differentiation Strategies
For Struggling Students
Use whole numbers of half-lives first (50%, 25%, 12.5%) and read ages from the decay curve in Diagram 2 before using logarithms
Give an evidence organizer with three columns (Earth materials, meteorites, other planetary surfaces) and one row per claim
Provide sentence starters for the account: "Earth formed about ___ ago. We know this because ___."
For Advanced Students
Ask students to explain why the U-238 and U-235 clocks in the same zircon give a check on each other, and what a disagreement would mean
Have students research the giant-impact hypothesis for the Moon and evaluate which observations support it and which remain open questions
Ask students to estimate how the crater density of a surface would change if its impact rate had been much higher early in solar system history
Assessment Guidance
What to Look For
Check that students count half-lives correctly (parent fraction (1/2)n, not 1/n) and that their ages fall within Earth's 4.6-billion-year history. Look for accounts that name evidence from all three sources (Earth materials, meteorites, other planetary surfaces) and explain why Earth's own record is incomplete. Listen for students who think Earth's oldest rock gives the age of Earth, or that the Moon was hit more often than Earth.
02
Classroom Activities
3 Activities
1
Penny Half-Life Model
20 minGroups of 3
Groups model radioactive decay with 100 pennies in a shoebox. Each shake stands for one half-life. They graph their data, compare it with Diagram 2, and use the model to date a meteorite.
Procedure
Put 100 pennies heads up in the box (parent atoms), close the lid and shake gently.
Remove every penny that lands tails up (it has "decayed" into a daughter atom) and record how many parent pennies remain.
Repeat until fewer than 3 pennies remain, then pool class data.
Safety: keep lids closed while shaking, pick up dropped coins right away so no one slips, and wash hands after handling coins.
Sample Data (invented)
Parent pennies after 0-6 shakes: 100, 52, 27, 13, 7, 4, 2. Students compare each value with the prediction 100 × (1/2)n: 100, 50, 25, 12.5, 6.25, 3.1, 1.6.
Discussion Questions
After 2 shakes, the group had 27 pennies instead of 25. Why is a small group of "atoms" noisier than the billions in a real mineral?
A mineral grain has 12.5% of its parent left. How many half-lives have passed? How would you turn that into an age?
Why can you not predict which penny will "decay" next, even though you can predict how many will?
Modification for Distance Learning
Students use 30 coins or a free online coin-flip simulator at home, record five rounds, and post their decay graph to the class discussion board.
2
Craters as Clocks
25 minGroups of 3-4
Groups make impact craters in a tray of flour, then count craters on printed images of the Moon and use an invented calibration from dated samples to estimate the age of a lunar surface.
Procedure
Fill a baking tray with 3 cm of flour and dust the top with a thin layer of cocoa powder so the ejected material shows.
Drop a marble from 0.5 m and then from 1.0 m, and measure each crater diameter. Drop a few more marbles close to earlier craters and watch how new craters cut across old ones, a clue to which formed first.
Count craters wider than a set size on two printed Moon images, one of highlands and one of mare, and divide by the area shown.
Safety: wear goggles, drop marbles from no higher than 1 m while standing on the floor, never throw them, and wipe up spilled flour so the floor is not slippery. Use dry sand instead of flour for any student with a wheat allergy.
Calibration and Sample Results (invented)
Calibration from dated Moon samples, in craters wider than 4 km per 1,000 km²: 3 craters on a 3.3-billion-year-old surface, 8 on a 3.8-billion-year-old surface, 24 on a 4.2-billion-year-old surface. Tray results: craters 4.0 cm wide from 0.5 m and 5.0 cm wide from 1.0 m. Unknown lunar region: 15 craters per 1,000 km².
Discussion Questions
Doubling the drop height made the crater only about 25% wider. What does that suggest about using crater size to judge the size of the impactor?
Between which two calibration ages does the unknown region fall? Why can crater counting alone rank surfaces but not give them an age in years?
Why would the same method fail on most of Earth's surface?
Challenge Variation
Groups predict, then test, whether a marble dropped at an angle makes a round crater, and explain what that means for reading impact directions on the Moon.
3
Evidence Cards: Build Earth's First Chapter
25 minGroups of 3-4
Groups receive eight evidence cards, sort them by source (Earth materials, meteorites, other planetary surfaces), arrange them on a timeline, and write a group account of Earth's formation and early history.
The Eight Cards
1. The oldest solid grains in meteorites are 4.567 billion years old.
2. Iron meteorites are pieces of metal cores from small early bodies that melted and separated into layers.
3. Zircon grains from Western Australia are up to about 4.4 billion years old.
4. The oldest known Earth rock, the Acasta Gneiss in Canada, is about 4.0 billion years old.
5. The oldest Moon highland rocks are about 4.3-4.5 billion years old, and mare basalts are about 3.1-3.9 billion years old.
6. The Moon's highlands are covered by overlapping craters; Earth has only about 200 confirmed impact structures.
7. Mercury, Venus, Earth and Mars are small and dense; Jupiter, Saturn, Uranus and Neptune are large and much less dense.
8. Moon rocks are similar in composition to Earth's mantle, and the Moon's average density is much lower than Earth's.
Task
Sort the cards by source and place the dated ones on a timeline from 4.6 to 3.0 billion years ago.
Write a group account of at least six sentences, citing a card number for each claim.
Mark each card as direct evidence (a measured age or property) or indirect evidence (an inference from a pattern).
Discussion Questions
Card 1 is older than every Earth material by more than 150 million years. Why do scientists still say Earth is about 4.6 billion years old?
Which two cards together best support the idea that Earth melted and formed an iron core early?
What might explain the gap between the oldest zircons (Card 3) and the oldest rock (Card 4)?
Modification for Distance Learning
Share the cards as a slide deck. Students drag them onto a shared timeline and write their account in a shared document.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Timeline of the Oldest Dated Materials
Approximate published ages placed to scale on a timeline from 4.6 to 3.0 billion years ago. Meteorites record the formation of the solar system, zircon crystals record Earth's first crust, and Moon rocks record the Moon's early surface and its later lava flows. Earth's surface keeps very little rock from its first 500 million years.
Diagram 2: Radioactive Decay of a Parent Isotope
The percent of parent atoms remaining after each half-life, drawn to scale: 100 × (1/2)n. The same curve fits every radioactive isotope; only the length of the half-life changes. Reading the fraction left in a sample gives the number of half-lives, and multiplying by the half-life gives the age.
04
Homework Assignment
~30 min
HS-ESS1-6 Homework: Reading Earth's Early History
Directions: Use the half-lives U-235 = 0.704, U-238 = 4.47 and K-40 = 1.25 billion years. Assume each sample started with no daughter atoms and has not gained or lost any. Data for invented samples and crater counts are labeled. Show each calculation, and end every problem with a sentence that states what the evidence tells you about Earth's early history.
Part 1: Radiometric Ages (Problems 1-2)
An invented meteorite grain that formed a little after the oldest solids has 1.02 atoms of lead-206 for every atom of uranium-238. (a) Find the number of half-lives. (b) Find the age of the grain. (c) Compare it with the age of Earth's oldest zircon and explain what the difference means.
An invented rock from Greenland has 2.4% of its original uranium-235 left. (a) Find its age. (b) Explain why Earth rocks this old are rare, while meteorites older than 4.5 billion years are common in collections.
Part 2: Planetary Surfaces and Compositions (Problems 3-4)
Invented crater counts on Mars (craters wider than 1 km): Region A has 1,080 craters on 30,000 km²; Region B has 240 on 40,000 km²; Region C, on the flank of a large volcano, has 12 on 24,000 km². (a) Find the crater density of each region per 1,000 km². (b) Rank the regions from oldest to youngest. (c) Explain what extra evidence is needed to turn the ranking into ages in years.
Use published values: Mercury has mass 3.30 × 10²³ kg and radius 2,440 km; the Moon has mass 7.35 × 10²² kg and radius 1,737 km. (a) Compute the average density of each in g/cm³. (b) Compare them with Earth (5.51 g/cm³). (c) Evaluate the claim that the Moon formed mostly from rocky material like Earth's mantle rather than from iron-rich material.
Part 3: Constructing an Account (Problems 5-6)
Place these on a timeline: oldest meteorite solids 4.567 billion years, an invented Moon highland rock 4.46 billion years, oldest Earth rock 4.03 billion years. (a) How many million years separate the first and second, and the second and third? (b) Write a four-sentence account of what was happening to Earth and the Moon during those two intervals, citing the evidence.
A student claims: "Earth is 4.0 billion years old, because that is the age of its oldest rock." Write a claim, evidence and reasoning response that uses evidence from Earth materials, meteorites and at least one other planetary surface.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Radiometric and Density Calculations
Half-lives, ages and densities computed correctly with units
Correct method with one calculation or unit error
Use of Evidence
Uses evidence from Earth materials, meteorites and other planetary surfaces, and says what each shows
Uses only one or two sources, or lists evidence without interpreting it
Account and Reasoning
Account of Earth's formation is logical and explains why Earth's own record is incomplete
Account stated but reasoning is missing or unclear
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Use the half-lives U-235 = 0.704, U-238 = 4.47 and K-40 = 1.25 billion years, and assume each sample started with no daughter atoms. Invented data are labeled. 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
Why do scientists date meteorites to find when the solar system formed, instead of dating the oldest rocks on Earth?
Answer: C
Most meteorites come from small asteroids that never had plate tectonics, weathering or erosion, so their oldest grains keep the clock that started when solids first formed. Choice D is false: Earth rocks are dated the same way, but its earliest crust has been recycled. Choice B is wrong because meteorites formed in our own solar system.
Question 2 of 20 · Multiple Choice
A mineral grain has 25% of its original potassium-40 left (half-life 1.25 billion years). How old is it?
Answer: B
25% is (1/2)², so 2 half-lives have passed: 2 × 1.25 = 2.5 billion years. Choice A divides the half-life by 4. Choice C reads the fraction 1/4 as 4 half-lives, instead of 1/4 = (1/2)² = 2 half-lives. Choice D is one half-life, which leaves 50%.
Question 3 of 20 · Multiple Choice
A mineral grain has 1/32 of its original parent atoms left. How many half-lives have passed?
Answer: D
(1/2)⁵ = 1/32, so 5 half-lives have passed. Choice A reads the fraction 1/32 as 32 half-lives, as if the fraction left were 1/n instead of (1/2)n, choice B is half of 32, and choice C counts one half-life too many (1/64).
Question 4 of 20 · Multiple Choice
Which explanation best accounts for the small number of impact craters on Earth compared with the Moon?
Answer: A
Earth is a larger target with stronger gravity, so it has been hit at least as often. Its surface is recycled at plate boundaries and worn down by water, wind and ice, so old craters are destroyed. Choice B contradicts this, and choice C gets gravity backward.
Question 5 of 20 · Multiple Choice
Invented counts: Region P on Mercury has 30 craters per 1,000 km² and Region Q has 6 per 1,000 km². What can you conclude?
Answer: C
An older surface has collected impacts for longer, so the region with 5 times more craters per unit area is older. Choice A reverses the logic. Choice D does not follow, because the counts say how many craters there are, not how large the impactors were.
Question 6 of 20 · Multiple Choice
Earth's average density is about 5.5 g/cm³, but the rocks at its surface are about 2.7-3.0 g/cm³. What does this evidence best support?
Answer: B
If the average is much higher than the surface, the interior must be much denser. Iron sank to the center when early Earth was hot enough to melt, a process also recorded in iron meteorites. Choice A would lower the average density, and choice D conflicts with Jupiter's density of about 1.3 g/cm³.
Question 7 of 20 · Multiple Choice
An invented lunar lava sample has 6.25% of its original uranium-235 left (half-life 0.704 billion years). How old is it?
Answer: C
6.25% = (1/2)⁴, so 4 half-lives: 4 × 0.704 ≈ 2.82 billion years. Choice A multiplies 0.704 by 6.25, the percent left, instead of the number of half-lives. Choice B divides by 4, and choice D counts only 2 half-lives.
Question 8 of 20 · Multiple Choice
Zircon grains 4.4 billion years old are found inside a sedimentary rock that is about 3 billion years old. What does this tell you?
Answer: D
Sedimentary rock is made of grains worn from older rocks, so its grains can be older than the rock itself. The zircons record crust that existed by 4.4 billion years ago, even though that crust has not survived. Choice B misunderstands how sedimentary rock forms.
Question 9 of 20 · Multiple Choice
Apollo samples show that the Moon's heavily cratered highlands are older than 4 billion years, while the smoother dark maria are about 3.1-3.9 billion years old. How does this support crater counting?
Answer: A
The measured ages agree with the crater pattern: more craters, older surface. That lets scientists use dated samples to turn crater densities into approximate ages elsewhere. Choice C is wrong because the maria have craters, just fewer of them.
Question 10 of 20 · Multiple Choice
The inner planets are small, rocky and dense, while the outer planets are large and made mostly of gas and ice. What does this pattern suggest about how the planets formed?
Answer: C
Solar system bodies formed from one disk of gas and dust, and temperature sorted the material: rock and metal near the Sun, ices and gas farther out. Choice B conflicts with the similar meteorite and planetary ages, and choice A cannot explain the sorting.
Question 11 of 20 · Multiple Choice
A mineral has 7 atoms of lead-207 for every atom of uranium-235 left (half-life 0.704 billion years). What is its age?
Answer: A
Daughter ÷ parent = 2n - 1 = 7, so 2n = 8 and n = 3 half-lives: 3 × 0.704 ≈ 2.11 billion years. Choice B multiplies the ratio 7 by the half-life, choice C divides the half-life by 7, and choice D counts only 2 half-lives.
Question 12 of 20 · Multiple Choice
Which observation supports the leading hypothesis that the Moon formed from debris after a large body collided with the early Earth?
Answer: A
Debris blasted mostly from Earth's outer layers would be rocky and poor in iron, matching Moon rocks and the Moon's low average density. Choice B is true of many bodies and says nothing about origin. Choice C describes its orbit, not its formation.
Question 13 of 20 · Multiple Choice
What do iron meteorites suggest about bodies in the early solar system?
Answer: B
Iron meteorites look like the metal core of a differentiated body that was later broken apart by collisions. That supports the idea that early bodies, including Earth, were heated enough to melt and sort into layers. Choice A ignores stony meteorites, and choice C is not supported by their composition.
Question 14 of 20 · Multiple Choice
The oldest meteorite grains are 4.567 billion years old, and the oldest known Earth rock is about 4.0 billion years old. Which conclusion is best supported by all the evidence?
Answer: B
Meteorites date the formation of the solar system's first solids, 4.4-billion-year zircons show Earth had crust soon after, and Moon rocks give similar early ages. The missing record between 4.567 and 4.0 billion years is explained by recycling of Earth's surface. Choice A mistakes the oldest surviving rock for the age of the planet.
Question 15 of 20 · Short Answer
An invented highland sample has 1.25% of its original uranium-235 left (half-life 0.704 billion years). Find its age and say which body it most likely came from.
n = log2(100 ÷ 1.25) = log2 80 ≈ 6.32 half-lives, so the age ≈ 6.32 × 0.704 ≈ 4.45 billion years. That fits the Moon's highlands (or a meteorite): no known Earth rock is that old.
Question 16 of 20 · Short Answer
Invented counts: a 30,000 km² region on the Moon has 540 craters, and a second 30,000 km² region has 120. Find the crater density of each per 1,000 km² and state which surface is older and by how many times its crater density is larger.
Region 1: 540 ÷ 30 = 18 per 1,000 km². Region 2: 120 ÷ 30 = 4 per 1,000 km². Region 1 is older, with 4.5 times the crater density.
Question 17 of 20 · Short Answer
Mars has mass 6.42 × 10²³ kg and radius 3,390 km. Compute its average density and compare it with Earth's 5.51 g/cm³. What does the comparison suggest?
V = 4/3 π (3.39 × 10⁶ m)³ ≈ 1.63 × 10²⁰ m³, so density ≈ 6.42 × 10²³ ÷ 1.63 × 10²⁰ ≈ 3,930 kg/m³ = 3.93 g/cm³. Mars is rocky like Earth but less dense, so it has a smaller iron core relative to its size and is less compressed by its own gravity.
Question 18 of 20 · Short Answer
In four to six sentences, construct an account of Earth's formation and first 600 million years. Cite at least one piece of evidence from Earth materials, meteorites and another planetary surface.
A strong answer: Earth formed about 4.6 billion years ago from the same disk of dust and gas as the rest of the solar system, as shown by 4.567-billion-year-old meteorite grains. It grew hot enough to melt, and iron sank to form a core, which explains its high average density and matches iron meteorites. Solid crust existed by about 4.4 billion years ago (zircons). Impacts were frequent, as the Moon's cratered highlands show, but plate tectonics and erosion have erased that record on Earth, so the oldest surviving rock is only about 4.0 billion years old.
Question 19 of 20 · Short Answer
A student says: "Mars's southern highlands have many more craters per square kilometer than its northern lowlands, so more space rocks must have hit the south." Evaluate the claim and give a better explanation.
The claim is not the best explanation. Impacts strike both hemispheres at about the same rate, so a difference in crater density points to a difference in surface age: the southern highlands are older and have collected craters for longer, while the northern lowlands were later resurfaced (for example by lava flows or sediment) and have had less time to collect craters.
Question 20 of 20 · Short Answer
Five invented meteorite grains give ages of 4.564, 4.566, 4.565, 4.567 and 4.568 billion years. Find the mean and the range, and explain what the result shows.
Mean = 22.830 ÷ 5 = 4.566 billion years; range = 4.568 - 4.564 = 0.004 billion years (4 million years). Different grains agree closely, which shows the first solids of the solar system formed within a few million years of each other and gives a reliable starting date for Earth's history.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-ESS1-6 mean?
HS-ESS1-6 asks students to use evidence from old Earth minerals, meteorites and the surfaces of other planets and moons to explain how Earth formed and what its early history was like. The heart of it is reasoning from evidence, not memorizing dates. The code stands for High School, Earth and Space Science, core idea 1 (Earth's Place in the Universe), performance expectation 6.
Is HS-ESS1-6 Earth science or astronomy?
It is usually taught in a high school Earth and Space Science course, often in a unit on Earth history or the solar system. It uses both geology (rocks and minerals) and planetary science (meteorites, the Moon and other planets), which is why it fits well between an astronomy unit and a plate tectonics unit.
Does HS-ESS1-6 have an assessment boundary?
No. NGSS lists no Assessment Boundary for HS-ESS1-6. The Clarification Statement sets the focus on evidence from within the solar system and names three examples: absolute ages from radiometric dating, the sizes and compositions of solar system objects, and impact cratering records.
How do we know Earth is 4.6 billion years old if its oldest rock is younger?
The age comes from the solar system as a whole. Meteorites, which formed with the planets and were never recycled, give ages of about 4.57 billion years, and Moon rocks and Earth's oldest zircon crystals are only slightly younger. Earth's surface rocks are younger because plate tectonics and erosion have destroyed the earliest crust.
What is radiometric dating in simple terms?
It is a clock based on radioactive decay. Some atoms change into other atoms at a steady, known rate, measured by the half-life. By measuring how much of the original (parent) isotope is left compared with the new (daughter) isotope, scientists work out how many half-lives have passed and so how long ago the mineral formed.
What math do students need for HS-ESS1-6?
Powers of one half, density (mass divided by volume), rates per unit area and reading graphs. Logarithms (n = log2 of 1 ÷ the fraction left) help when the number of half-lives is not a whole number, but students can also read ages from a decay curve or use a spreadsheet.
What do impact craters tell us about the early solar system?
Crater density works as a relative clock: surfaces with more craters per unit area are older. On the Moon, dated Apollo samples calibrate the count, and the heavily cratered highlands show that impacts were frequent early in solar system history. Other bodies, such as Mercury and Mars, preserve similar old surfaces.
What misconceptions do students have about Earth's early history?
A frequent one is that the oldest rock on Earth gives the age of Earth. Others are that radioactive decay makes the whole sample disappear after two half-lives, that the Moon was hit more often than Earth, and that planets formed one at a time over billions of years. Each can be tested against the evidence on this page.
Can students do HS-ESS1-6 without lab equipment?
Yes. Pennies or dice model decay, a tray of flour and a marble model cratering, and free image archives of the Moon and Mars let students count craters. The core practice is constructing an account from evidence, which works with data tables and evidence cards.
How does HS-ESS1-6 connect to other standards?
It builds on MS-ESS1-4, where students use rock strata to organize Earth history. At the high school level it pairs with HS-ESS1-5 on the ages of crustal rocks and HS-PS1-8 on radioactive decay, and it leads to HS-ESS2-7 on how Earth's systems and life have changed together.
07
Related Standards
5 standards
These standards connect to HS-ESS1-6: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-ESS1-4Prerequisite
Explain how rock strata are used to organize Earth's 4.6-billion-year history
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