HS-ESS2-7NGSS*ScienceEarth and Space ScienceGrades 9-12
HS-ESS2-7: Arguing for the Coevolution of Earth and Life
In plain English: HS-ESS2-7 is the NGSS high school performance expectation that asks students to construct an argument from evidence that Earth's systems and life have changed together, each driving changes in the other. Examples include photosynthetic microbes adding oxygen to the air and coral reefs reshaping coastlines. It is usually taught in Earth and Space Science, and it connects to Biology.
Construct an argument based on evidence about the simultaneous coevolution of Earth systems and life on Earth.
Clarification Statement: Emphasis is on the dynamic causes, effects, and feedbacks between the biosphere and Earth's other systems, whereby geoscience factors control the evolution of life, which in turn continuously alters Earth's surface. Examples of include how photosynthetic life altered the atmosphere through the production of oxygen, which in turn increased weathering rates and allowed for the evolution of animal life; how microbial life on land increased the formation of soil, which in turn allowed for the evolution of land plants; or how the evolution of corals created reefs that altered patterns of erosion and deposition along coastlines and provided habitats for the evolution of new life forms.
Assessment Boundary: Assessment does not include a comprehensive understanding of the mechanisms of how the biosphere interacts with all of Earth's other systems.
Next Generation Science Standards · Disciplinary Core Idea: Earth's Systems · Official standard
Students build arguments from evidence that life and the rest of the Earth system have changed each other over billions of years. The lesson follows three chains from the standard: photosynthetic microbes put oxygen into the air and oceans, which sped up weathering and allowed animals to evolve; microbes on land helped form soil, which allowed land plants; and corals built reefs that changed how coastlines erode and gave new species places to live. Students weigh rock and fossil evidence, add simple calculations, and answer counterclaims.
The NGSS Clarification Statement says: "Emphasis is on the dynamic causes, effects, and feedbacks between the biosphere and Earth's other systems, whereby geoscience factors control the evolution of life, which in turn continuously alters Earth's surface. Examples of [sic] include how photosynthetic life altered the atmosphere through the production of oxygen, which in turn increased weathering rates and allowed for the evolution of animal life; how microbial life on land increased the formation of soil, which in turn allowed for the evolution of land plants; or how the evolution of corals created reefs that altered patterns of erosion and deposition along coastlines and provided habitats for the evolution of new life forms." The Assessment Boundary says: "Assessment does not include a comprehensive understanding of the mechanisms of how the biosphere interacts with all of Earth's other systems." So students argue from the evidence for each link in a chain; they do not need the full chemistry of every interaction. Dates are rounded, and ages for early events carry uncertainties of tens of millions of years or more. All lab and field data sets are invented and labeled that way. Students do the practice of arguing from evidence: they make a claim, choose evidence, explain the reasoning and rebut a counterclaim.
Learning Objectives
By the end of this lesson, students will be able to:
Construct an argument with a claim, evidence and reasoning that life and Earth's other systems have changed each other over time
Interpret rock and fossil evidence, such as banded iron formations, ancient soils, root traces and fossil reefs, as support for a link in a coevolution chain
Describe the oxygen, soil and coral reef chains as feedbacks in which a change in life alters an Earth system, which then allows new life
Use rates, time spans and percentages from data to strengthen an argument
Evaluate a counterclaim and write a rebuttal based on evidence
Prior Knowledge Required
Students should already be comfortable with:
Using rock strata and the geologic time scale to organize Earth's history MS-ESS1-4
Patterns in the fossil record that show how life has changed MS-LS4-1
The role of photosynthesis in the cycling of matter and energy MS-LS1-6
How geoscience processes such as weathering and erosion change Earth's surface MS-ESS2-2
"Beavers dam a stream and turn it into a pond. The pond floods the valley, and frogs, ducks and new plants move in. Did the beavers change the land, or did the land change which animals live there? Give one example of each direction."
Collect answers on a T-chart labeled "life changes Earth" and "Earth changes life". Point out that both columns fill up. Today's standard asks for the same two-way reasoning over billions of years, with rocks and fossils as evidence.
Direct Instruction15-20 minutes
Coevolution and the shape of an argument. Coevolution of Earth systems and life means that changes in living things alter the atmosphere, hydrosphere or geosphere, and those changes then control which new life can evolve. Model the argument structure: a claim (a statement that can be tested), evidence (observations from rocks, fossils or measurements) and reasoning (why the evidence supports the claim). Then add a counterclaim and a rebuttal. Use Diagram 1 for the timeline and Diagram 2 for the three chains.
Photosynthesis changes the atmosphere
Claim: oxygen made by photosynthetic microbes, not a nonliving source, built up in the air about 2.4 billion years ago. Evidence: fossil microbial mats (stromatolites) are known from about 3.5 Ga; banded iron formations, layers of iron oxide laid down in seawater, are common from 2.8 to 1.8 Ga; grains of pyrite and uraninite, minerals that break down when oxygen is present, are found in river sand older than about 2.4 Ga but not in younger river sand.
Result: Reasoning: oxygen made in the ocean first reacted with dissolved iron and settled out as iron oxide, so it did not reach the air at once. Once these oxygen sinks could no longer keep up, oxygen collected in the air and began to destroy pyrite grains during weathering.
Oxygen changes weathering, then animals evolve
After oxygen built up, weathering on land began to oxidize minerals such as pyrite, sending more sulfate and nutrients to the sea. Oxygen high in the atmosphere also formed an ozone layer. Large animals appear in the fossil record at about 575 Ma, in the Ediacaran.
Result: Earth is about 4,540 million years old, so large animals have existed for 575 ÷ 4,540 ≈ 13% of Earth's history. The argument: large, active animals need oxygen-rich water, and that condition came from billions of years of photosynthesis. Here the Earth system (the atmosphere) controls the evolution of life.
Microbes build soil, then plants follow
An invented field study compares plots on the same kind of rock. Plots with a microbial crust (bacteria, algae and fungi on the surface) gain soil at 0.025 mm per year; bare plots gain 0.005 mm per year.
Result: The crust speeds soil formation 0.025 ÷ 0.005 = 5 times. At these rates, 20 cm (200 mm) of soil takes 200 ÷ 0.025 = 8,000 years with the crust and 40,000 years without it. Rooted plants need that soil, so microbial life prepared the land for the first land plants, about 470 Ma.
Land plants change rivers and the air
In rocks older than about 450 Ma, river deposits show mostly wide, braided channels of sand and gravel. After land plants with roots spread in the Silurian and Devonian, river deposits more often show single, winding channels with muddy banks and fossil roots.
Result: Roots held banks together and trapped mud, so the pattern of erosion and deposition changed. Roots and soil acids also sped up rock weathering, which removes CO2 from the air. Life changed the geosphere and the atmosphere, and the new landscapes gave other organisms new places to live.
Corals change a coastline
Invented wave-gauge data: waves 2.0 m high offshore are 0.8 m high in the lagoon behind a reef. Wave energy is proportional to the square of wave height.
Result: Energy behind the reef = (0.8 ÷ 2.0)² = 0.16 of the offshore value, so the reef removes about 84% of the wave energy. Calm water lets sand and mud settle in the lagoon and protects the shore from erosion, and the reef's cracks and branches become habitat for fish, crabs and other species.
After each example, ask two questions: "Which part of the chain is life changing Earth, and which part is Earth changing life?" and "What evidence would a skeptic ask for?" Remind students that dates for events billions of years ago are estimates, and that an argument can be strong even when some mechanisms are still debated.
Guided Practice15 minutes
Pairs sort six pieces of evidence. For each one, they write what it shows and which direction of the chain it supports. The first row is done as a model.
Guided practice: sorting evidence for coevolution
Evidence
What it shows
Direction
Stromatolites, layered mounds built by microbial mats, in rocks about 3.5 Ga old
Microbial communities lived in shallow water very early
Evidence of early life (sets up both directions)
Banded iron formations, most 2.8-1.8 Ga
? (pairs fill in)
?
Ancient soils (paleosols) older than land plants with carbon from microbes
?
?
Burrows and large animal fossils appear after oxygen rose, about 575-540 Ma
?
?
Fossil tree roots in river bank deposits of Devonian age
?
?
A fossil reef with fine lagoon mud behind it and beach sand in front
?
?
Fill in the table. Mark each row "life changes Earth", "Earth changes life" or both.
Choose two rows that form one chain and write a two-sentence argument that links them with "which in turn".
Trade with another pair. Each pair names the weakest link in the other pair's argument and says what evidence would make it stronger.
Independent Practice10-15 minutes
Each student writes a claim, evidence and reasoning paragraph for the soil chain, using the invented data below from a study of volcanic rock surfaces of known age.
Independent practice: soil depth on rock surfaces of different ages (invented)
Surface age (years)
Soil depth with microbial crust (cm)
Soil depth, bare rock (cm)
2,000
4.0
0.8
4,000
8.0
1.6
6,000
12.0
2.4
Students should find rates of 0.02 mm per year with the crust and 0.004 mm per year without it, a factor of 5, and connect the faster soil formation to the later evolution of rooted plants. Ask them to add one limitation (for example, that modern crusts may not behave like ancient ones).
Closure5 minutes
Exit ticket: "Write one 'which in turn' sentence for the coral reef chain. Then write one piece of evidence you would want to see to test it." Look for a sentence that goes from corals to a change in erosion or deposition to new life, and for evidence that could be observed, such as sediment behind a fossil reef.
Differentiation Strategies
For Struggling Students
Give an argument frame: "I claim that ___. The evidence is ___. This supports the claim because ___. Someone might argue ___, but ___."
Provide the evidence cards with a short "what it shows" line on the back so students focus on linking evidence to a claim
Work through one chain (oxygen) as a class before students write about the soil or reef chain on their own
For Advanced Students
Ask students to rank the evidence for the oxygen chain from strongest to weakest and defend the ranking
Have students research how scientists date a banded iron formation or a fossil reef and explain one source of uncertainty in the date
Challenge students to propose a fourth chain from a different time in Earth's history, such as grasses and grazing animals, and outline the evidence it would need
Assessment Guidance
What to Look For
Check that every argument has both directions of the chain: life changing an Earth system, and that change allowing or shaping new life. Look for evidence that names a real observation (a rock type, a fossil, a measurement) rather than a restated claim. Listen for students who say the atmosphere "wanted" oxygen or that animals appeared because they "needed" to; steer them to cause and effect. Students do not need the full chemistry of weathering or reef growth.
02
Classroom Activities
3 Activities
1
Steel Wool Lab: Modeling Iron as an Oxygen Sink
25 minGroups of 3-4
Groups model why oxygen from early photosynthesis did not build up in the air at once. Iron in steel wool reacts with oxygen in trapped air, just as dissolved iron in early seawater reacted with oxygen and settled out as banded iron formations. One tube has iron in it; the other has none, like an ocean whose dissolved iron has already been used up.
Procedure
Wear goggles and gloves. Dip a 2.0 g piece of plain steel wool in white vinegar for 1 minute to remove any coating, then rinse with water.
Push the wool to the bottom of a dry test tube or 25 mL graduated cylinder (tube A). Leave a second, identical tube empty (tube B). Measure the length of the air column in each tube.
Turn each tube upside down in a beaker with 3 cm of water. Mark the water level with a marker.
Leave the tubes in a safe place until the next class, then measure how far the water has risen and look at the steel wool.
Safety: steel wool splinters, so handle it with gloves. It can catch fire: keep it away from flames, heat sources and batteries (a battery touching steel wool can ignite it). Vinegar is a weak acid: rinse splashes with water. Wipe up spilled water, and throw rusted steel wool in the trash, not the sink.
Sample Data (invented)
Tube A (steel wool): air column 20.0 cm, water rose 1.9 cm after 6 hours and 4.1 cm after one day, then stopped; part of the wool is still gray. Tube B (no iron): air column 20.0 cm, water rose 0.0 cm.
Discussion Questions
What fraction of the air in tube A was used up? Compare it with the 21% oxygen in today's air.
Tube A stopped rising even though some iron was left. What ran out?
Which tube is a model of the ocean before about 2.4 Ga, when dissolved iron removed oxygen as fast as microbes made it? Which models the time after, when oxygen could collect?
Name one way this model is different from the early ocean (for example, the source of oxygen, the timescale or the form of the iron).
Modification for Distance Learning
Students analyze the sample data and a teacher photo of both tubes, then write a paragraph linking the model to banded iron formations.
2
Wave Tank: How Reefs Change a Coastline
25 minGroups of 3-4
Groups build a model coastline in a plastic bin and test whether a reef changes erosion and deposition. They compare a beach with no reef and a beach with a line of flat stones standing in for a reef.
Procedure
Pile damp sand at one end of the bin into a sloping beach about 15 cm long. Add water 5 cm deep. Measure the distance from the end of the bin to the water line.
Trial 1 (no reef): push a flat paddle forward and back 20 times at a steady rate to make waves. Measure the new water line and note where sand settled.
Rebuild the beach. Trial 2 (reef): place a row of flat stones across the bin 20 cm from the beach, reaching just below the water surface, and repeat the 20 waves.
Safety: fill the bin where it will sit so no one carries a full bin. Wipe up spills at once so no one slips, keep water away from outlets and electronics, and wash hands after handling sand.
Sample Data (invented)
No reef: the water line moved 4.5 cm into the beach, and sand spread across the bottom of the bin. With the reef: the water line moved 1.2 cm, and a thin layer of fine sand settled in the calm water between the stones and the beach.
Discussion Questions
By what percent did the reef reduce beach erosion? (4.5 - 1.2 = 3.3 cm less, about 73% less.)
Where did sand settle in each trial, and why?
Real reefs are built by living corals over thousands of years. Use your data to argue how the evolution of corals changed coastlines, and what new habitats the calm water behind a reef provides.
What does the model leave out (reef growth, tides, living organisms, the scale of real waves)?
Challenge Variation
Leave gaps in the reef and predict, then test, where erosion and deposition change. Relate the result to channels through real reefs.
3
Evidence Card Argument: Who Changed Whom?
25 minGroups of 4 (two pairs)
Each group gets 8 evidence cards. One pair argues "life changed Earth's systems"; the other argues "Earth's systems controlled the evolution of life". After a first round, both pairs must write a joint claim that uses evidence from both sides.
Evidence Cards
Stromatolites about 3.5 Ga old show that microbial mats lived in shallow seas.
Banded iron formations are common from 2.8 to 1.8 Ga.
River sand older than about 2.4 Ga contains pyrite grains that break down when oxygen is present.
Ancient soils from before land plants contain carbon left by microbes.
The first spores of land plants are found in rocks about 470 Ma old.
Large animal fossils appear about 575 Ma, after a second rise in oxygen.
Devonian river deposits show fossil roots in muddy, winding channel banks.
Fossil reefs have fine lagoon mud on the landward side and many species of fossil shells living among the corals.
Structure
Round 1 (8 minutes): each pair chooses at least three cards and writes a claim, evidence and reasoning statement.
Round 2 (6 minutes): each pair presents for 2 minutes and the other pair offers one counterclaim.
Round 3 (8 minutes): the group writes a joint claim using "which in turn" at least twice, with at least four cards as evidence.
Debrief (3 minutes): which cards did both pairs use, and why?
Discussion Questions
Cards 2 and 3 are about minerals, not fossils. How can nonliving evidence support a claim about life?
Which cards show a gap of hundreds of millions of years between a change and the life that followed? What might explain the gap?
Did any card fit only one side? Defend your answer.
Modification for Distance Learning
Put the cards on a shared slide. Pairs work in breakout rooms, then post their joint claim to a class discussion thread and reply to one other group.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Timeline of Earth and Life
Key events on a to-scale timeline from Earth's formation to today (dates rounded; early dates are uncertain by tens of millions of years or more). Oxygen-related rock evidence clusters around 2.4 Ga, while animals, land plants, forests and modern reef-building corals all fall in the last 13% of Earth's history.
Diagram 2: Three Chains of Coevolution
The three examples in the NGSS Clarification Statement, drawn as chains: a change in life alters an Earth system, and that change allows new life. The dashed arrows show that the new life keeps changing Earth's surface.
04
Homework Assignment
~30 min
HS-ESS2-7 Homework: Arguing from Evidence About Earth and Life
Directions: All data sets are invented for practice, and dates are rounded. For every problem, state a claim, cite the evidence and explain your reasoning. Show calculations with units.
Part 1: Evaluating Evidence (Problems 1-2)
River sand samples of different ages were checked for pyrite grains (grains per kilogram of sand): 3.0 Ga: 40; 2.8 Ga: 35; 2.6 Ga: 38; 2.45 Ga: 20; 2.3 Ga: 0; 2.1 Ga: 0. Red, iron-stained sandstones appear only in the 2.1 Ga sample. (a) By what percent did the pyrite count drop from 2.6 to 2.45 Ga? (b) Make a claim about when oxygen collected in the air, and support it with both kinds of evidence. (c) What would a counterclaim need to explain?
An invented banded iron formation is 150 m thick and was laid down over 3 million years. (a) Find the average rate of deposition in mm per year. (b) Explain what each iron oxide layer tells you about the oxygen and the dissolved iron in the ocean at that time. (c) Explain how this rock is evidence that life changed the hydrosphere.
Part 2: Chains of Cause and Effect (Problems 3-4)
Soil depths on invented test surfaces of known age: with microbial crust, 1.5 cm at 1,000 years, 4.5 cm at 3,000 years and 7.5 cm at 5,000 years; bare, 0.5 cm, 1.5 cm and 2.5 cm. (a) Find the rate of soil formation for each surface in mm per year. (b) How many times faster is soil formation with the crust? (c) Write a two-sentence argument that uses the result to connect microbial life to the evolution of land plants.
An invented study compares two small watersheds on the same granite. Stream water from the forested watershed carries 12 mg of dissolved calcium per liter; stream water from a bare, rocky watershed carries 4 mg per liter. (a) How many times more calcium does the forested stream carry? (b) Explain how plant roots could cause the difference. (c) Faster weathering removes CO2 from the air. Build a chain from the evolution of land plants to a change in the atmosphere.
Part 3: Constructing Arguments (Problems 5-6)
Invented wave data: waves 1.8 m high arrive at a reef, and waves 0.6 m high reach the beach behind it. Wave energy is proportional to the square of wave height. (a) What fraction of the wave energy reaches the beach? (b) By what percent does the reef reduce wave energy? (c) Use the result to argue how the evolution of corals changed patterns of erosion and deposition and provided habitats for new life.
Write a full argument (claim, three pieces of evidence, reasoning, counterclaim and rebuttal) for this claim: "Earth's systems and life have evolved together, each changing the other." Use evidence from at least two of the three chains in Diagram 2. The counterclaim to answer: "Life only adapted to Earth; it did not change the planet."
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Claim
Clear, testable claim that names both directions of change
Claim names only one direction or is vague
Evidence
Specific observations or calculated values from the data, correctly computed
Evidence is general, or a calculation has an error
Reasoning
Explains how each piece of evidence supports the claim, linking cause and effect
Evidence and claim are listed without a clear link
Counterclaim and Rebuttal
States a real counterclaim and answers it with evidence
Counterclaim stated but not answered with evidence
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented and dates are rounded. 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
What does "coevolution of Earth systems and life" mean?
Answer: B
Coevolution works in both directions: life changes the atmosphere, oceans or land, and those changes control which new life can evolve. Choice A leaves out life changing Earth. Choice C confuses coevolution with the timing of Earth's formation.
Question 2 of 20 · Multiple Choice
A red sandstone formed on land 2.2 billion years ago. Its sand grains are coated with iron oxide. What does this suggest about the environment where it formed?
Answer: A
Iron oxide forms when iron reacts with oxygen, so red coatings on land-deposited grains point to oxygen in the air. Choice B contradicts the iron oxide. Choice C ignores that the rock formed on land, and choice D has no support: animals did not yet exist.
Question 3 of 20 · Multiple Choice
In a steel wool tube with a 25.0 cm air column, the water has risen 2.5 cm after 3 hours, and the wool is still mostly gray. What percent of the trapped air has been used so far, and what do you predict by the next day?
Answer: C
2.5 ÷ 25.0 = 0.10, so 10% of the air has been used so far. Iron is left and oxygen is left, so the reaction keeps going until the oxygen, about one fifth of air, is used up. Choice A treats centimeters as a percent. Choice D ignores that both reactants remain, and choice B is the part of the air not yet used.
Question 4 of 20 · Multiple Choice
Which new finding would most weaken the claim that photosynthetic life caused oxygen to build up in the air?
Answer: D
A cause must come before its effect, so oxygen that built up before any oxygen-making life would undercut the claim. Choices A, B and C fit the existing argument and would strengthen it.
Question 5 of 20 · Multiple Choice
Waves 1.2 m high reach a reef, and waves 0.3 m high reach the beach behind it. Wave energy is proportional to the square of wave height. By about what percent does the reef reduce the wave energy?
Answer: B
Energy fraction = (0.3 ÷ 1.2)² = 0.0625, so the reef removes about 94% of the energy. Choice A uses the height ratio without squaring. Choice D is the fraction that gets through, not the fraction removed, and choice C is the height fraction.
Question 6 of 20 · Multiple Choice
Which sequence describes the soil chain from the Clarification Statement?
Answer: D
Microbes on bare land sped up weathering and added organic matter, building soil that rooted plants later needed. Choice A reverses the order. Choice C mixes the reef chain into the soil chain.
Question 7 of 20 · Multiple Choice
Modern reef-building corals appeared about 240 Ma, and large animals about 575 Ma. For roughly what percent of the time since large animals appeared have modern reef-building corals existed?
Answer: C
240 ÷ 575 ≈ 0.42, about 42%. Choice B is the remaining 58%. Choice D divides the wrong way (575 ÷ 240 ≈ 2.4), and choice A divides by the age of Earth (240 ÷ 4,540 ≈ 5%) instead of by the time since large animals appeared.
Question 8 of 20 · Multiple Choice
How does a reef change deposition along a coastline?
Answer: A
By breaking waves, a reef leaves a quieter lagoon where fine sediment can settle instead of being carried away. Choice B reverses the effect on waves. Choice D ignores the wave data.
Question 9 of 20 · Multiple Choice
A student claims that the oxygen in the air came from volcanoes, not from life. Which is the best rebuttal?
Answer: D
Volcanoes release very little free oxygen, and some of their gases remove it, so they cannot explain an oxygen-rich atmosphere; photosynthesis releases O2 directly. Choice B is false, since volcanoes have erupted through all of Earth's history. Choices A and C are not supported by evidence.
Question 10 of 20 · Multiple Choice
Soil forms at 0.04 mm per year under a microbial crust. How long would it take to form 36 cm of soil?
Answer: A
36 cm = 360 mm, and 360 ÷ 0.04 = 9,000 years. Choice B uses 36 without converting centimeters to millimeters, and choice C adds a zero. Choice D multiplies 360 × 0.04 instead of dividing.
Question 11 of 20 · Multiple Choice
Which statement describes an Earth system shaping the evolution of life, rather than life changing Earth?
Answer: D
Here the ocean-atmosphere system is the cause and the evolution of animals is the effect. Choices A, B and C all have life as the cause of a change in an Earth system.
Question 12 of 20 · Multiple Choice
Which evidence would best support the claim that early land plants changed how rivers erode and deposit sediment?
Answer: A
The claim is about change over time, so the evidence must come from the rock record and link the new river pattern to plants. Choice B is a modern observation that shows a pattern but not a change. Choice C does not involve plants or channel shape.
Question 13 of 20 · Multiple Choice
Which reasoning statement best links the evidence "banded iron formations are common from 2.8 to 1.8 Ga" to the claim "early photosynthesis changed the oceans"?
Answer: B
Good reasoning explains why the evidence supports the claim: the layers record a reaction that needs oxygen, and oxygen came from photosynthesis. Choice D argues from age alone, which does not connect to oxygen. Choices A and C are not about the claim.
Question 14 of 20 · Multiple Choice
An invented banded iron formation is 60 m thick and formed over 2 million years. What was its average rate of deposition?
Answer: C
60 m = 60,000 mm, and 60,000 ÷ 2,000,000 = 0.03 mm per year. Choices A and B come from errors in the powers of ten when converting meters to millimeters, and choice D skips that conversion.
Question 15 of 20 · Short Answer
Write a claim, two pieces of evidence and reasoning for this question: How did the evolution of corals change coastlines and life along them?
Claim: corals built reefs that changed coastal erosion and deposition and created new habitats. Evidence: fossil reefs have fine lagoon mud on their landward side; wave measurements show much smaller waves behind reefs; fossil reefs contain many species living among the corals. Reasoning: reefs break waves, so less wave energy reaches the shore, erosion slows and fine sediment can settle; the reef structure and calm lagoon give organisms new places to live, where new species could evolve.
Question 16 of 20 · Short Answer
In an invented oxygen budget, photosynthesis adds 100 units of oxygen per year to the ocean and dissolved iron removes 99 units per year. Later, the iron runs low and removes only 60 units per year. How much faster does oxygen build up later? Explain what this model says about the timing of oxygen in the air.
Early: 100 - 99 = 1 unit per year. Later: 100 - 60 = 40 units per year, so oxygen builds up 40 times faster. The model shows that oxygen could be made for a long time without collecting, because iron removed almost all of it. Oxygen appeared in the air only after the sinks weakened, which explains a delay between oxygen-making life and oxygen in the air.
Question 17 of 20 · Short Answer
The Clarification Statement says life and Earth systems change "simultaneously" and "continuously". Explain what this means, using the oxygen chain.
The changes are not one-time events: while microbes added oxygen, the oxygen was already changing weathering and the chemistry of the oceans, and those changes affected which organisms could live there, which in turn changed how much oxygen was made. Each part of the system responds to the others at the same time, over long periods, so the atmosphere and life changed together.
Question 18 of 20 · Short Answer
A classmate says: "The atmosphere changed first, and life simply adapted to it." Write a rebuttal using at least two pieces of evidence.
The rock record shows life changing the atmosphere, not only adapting. Stromatolites show microbial life more than a billion years before oxygen built up; banded iron formations and the loss of pyrite grains from river sand after about 2.4 Ga show oxygen being added by that life. Oxygen-rich air then allowed animals to evolve, so change went in both directions.
Question 19 of 20 · Short Answer
Plan a comparison that would test the claim "microbial crusts speed up soil formation." Name what you would measure, what you would compare and what you would keep the same.
Compare soil depth (or the amount of fine, weathered material) on rock surfaces with and without microbial crust. Keep the same rock type, age of surface, climate and slope, and use several plots of each kind. Measure soil depth at many points in each plot. If the crusted plots have deeper soil for the same age, the data support the claim.
Question 20 of 20 · Short Answer
In an invented wave tank test, 12 cm³ of fine sand settled in the calm zone behind a model reef, compared with 3 cm³ in the same zone with no reef. Compute the ratio and write a one-sentence claim that uses it.
Ratio = 12 ÷ 3 = 4 times as much sand. Claim: the model reef made the water behind it calm enough that four times as much fine sand was deposited, which supports the idea that coral reefs change patterns of deposition along coastlines.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-ESS2-7 mean?
HS-ESS2-7 asks students to construct an argument, backed by evidence, that Earth's systems and life have changed together, each affecting the other. The focus is on the argument: a claim, evidence from rocks and fossils, reasoning and a response to counterclaims. The code stands for High School, Earth and Space Science, core idea 2 (Earth's Systems), performance expectation 7.
Is HS-ESS2-7 taught in Earth science or biology?
It is an Earth and Space Science performance expectation and is usually taught there, but it pairs well with the evolution unit of Biology. It uses fossil evidence from biology and rock evidence from geology, so it works as a bridge between the two courses.
What is the assessment boundary for HS-ESS2-7?
The boundary says assessment does not include a comprehensive understanding of the mechanisms of how the biosphere interacts with all of Earth's other systems. Students need to argue from evidence for each link in a chain, such as oxygen and weathering, but not explain every chemical reaction or every interaction.
What was the Great Oxidation Event?
It is the time, around 2.4-2.3 billion years ago, when oxygen first built up in Earth's atmosphere. Before then, the air had almost no free oxygen. Scientists link it to oxygen made by photosynthetic microbes, and the exact timing and causes of the delay are still being studied.
Does coevolution mean Earth is alive?
No. Coevolution here means that living and nonliving systems affect each other, as when plants change soil and soil changes which plants can grow. The standard does not require any idea that Earth is a living organism, and a lesson can stay with evidence of cause and effect.
Why do dates for events like the first land plants differ between sources?
Dates depend on which fossils or rocks are found and how they are dated, and new finds can push a date earlier. Early events are also dated with larger uncertainties. This page uses rounded dates; students should expect small differences between textbooks and focus on the order of events.
How do I teach argumentation for this standard?
Use a claim-evidence-reasoning structure and add a counterclaim and rebuttal. Give students real types of evidence, such as rock layers, fossils and invented measurements, and ask them to link each piece to the claim with "because". Short, structured debates with evidence cards help students hear and answer counterclaims.
What safety steps do the labs on this page need?
For the steel wool lab, wear goggles and gloves, keep steel wool away from flames, heat and batteries because it can ignite, and rinse vinegar splashes with water. For the wave tank, fill the bin where it sits, wipe up spills to prevent slips and keep water away from outlets. Wash hands after both labs.
How does HS-ESS2-7 connect to the carbon cycle and climate?
Many coevolution chains move carbon: photosynthesis takes CO2 from the air, roots speed up weathering that removes CO2, and corals store carbon in limestone. Those links connect this standard to the carbon cycle model in HS-ESS2-6 and to the climate model in HS-ESS2-4.
How should I grade a coevolution argument?
Grade the claim, evidence, reasoning and rebuttal separately, as in the rubric on this page. A strong argument names both directions of change, uses specific evidence and explains how it supports the claim. Length matters less than whether each piece of evidence is tied to the claim.
07
Related Standards
5 standards
These standards connect to HS-ESS2-7: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-ESS1-4Prerequisite
Use rock strata to explain how the geologic time scale organizes Earth's history
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