MS-ESS1-4NGSS*ScienceEarth and Space ScienceGrades 6-8
MS-ESS1-4: Using Rock Strata to Explain the Geologic Time Scale
In plain English: MS-ESS1-4 is the NGSS middle school performance expectation that asks students to construct a scientific explanation, based on evidence from rock strata, of how the geologic time scale organizes Earth's 4.6-billion-year history. Students order rock layers, faults and fossils by relative age and match layers between sites. It is usually taught in middle school Earth and space science.
Construct a scientific explanation based on evidence from rock strata for how the geologic time scale is used to organize Earth's 4.6-billion-year-old history.
Clarification Statement: Emphasis is on how analyses of rock formations and the fossils they contain are used to establish relative ages of major events in Earth's history. Examples of Earth's major events could range from being very recent (such as the last Ice Age or the earliest fossils of homo sapiens) to very old (such as the formation of Earth or the earliest evidence of life). Examples can include the formation of mountain chains and ocean basins, the evolution or extinction of particular living organisms, or significant volcanic eruptions.
Assessment Boundary: Assessment does not include recalling the names of specific periods or epochs and events within them.
Next Generation Science Standards · Disciplinary Core Idea: Earth's Place in the Universe · Official standard
Students construct scientific explanations, based on evidence from rock strata (layers of rock), of how the geologic time scale organizes Earth's 4.6-billion-year history. The geologic time scale is a calendar of Earth's past that splits it into long spans of time, from eons down to eras, periods and epochs. Students learn the rules geologists use to find relative ages (which rocks and events came first, without a number of years): younger layers lie on top of older ones, a crack or a body of cooled magma is younger than the rocks it cuts through, and the same fossils or the same ash layer mark rocks of the same age in different places. They read cross-sections, match layers between sites, and then see how dated layers turn the order into numbers of years.
The NGSS Clarification Statement says: "Emphasis is on how analyses of rock formations and the fossils they contain are used to establish relative ages of major events in Earth's history. Examples of Earth's major events could range from being very recent (such as the last Ice Age or the earliest fossils of homo sapiens) to very old (such as the formation of Earth or the earliest evidence of life). Examples can include the formation of mountain chains and ocean basins, the evolution or extinction of particular living organisms, or significant volcanic eruptions." The Assessment Boundary says: "Assessment does not include recalling the names of specific periods or epochs and events within them." So the page names a few divisions in tables for reference, but no quiz or homework item asks students to remember names: every item gives the data. Dates are published values, rounded. Cross-sections and data marked invented are made up for teaching. How labs measure ages with radioactive elements is beyond this standard.
Learning Objectives
By the end of this lesson, students will be able to:
Use superposition, cross-cutting relationships and erosion surfaces to put the rock layers and events in a cross-section in order
Match layers between sites using fossils and volcanic ash layers, and explain why this lets geologists build one record for the whole Earth
Explain how changes in fossils and dated layers are used to divide Earth's history into the units of the geologic time scale
Build a scale model of Earth's 4.6-billion-year history and place very old and very recent events on it
Construct a written explanation with a claim, evidence from strata and reasoning
Prior Knowledge Required
Students should already be comfortable with:
Patterns in rock layers and fossils show how a landscape changed over time 4-ESS1-1
Fossils show what kinds of organisms lived long ago and where 3-LS4-1
Sediment (sand, mud, shells) settles in layers and can harden into rock
Reading large numbers (millions and billions) and computing percents
Before class, stack four colors of modeling clay into a layered block, one color at a time, while students watch. Then push a pencil straight down through the whole stack.
Warm-Up Prompt
"I made this block one layer at a time and then pushed a pencil through it. Without asking me, how can you tell which layer I put down first and which last? Did the pencil go in before or after the top layer? Explain how you know."
Collect answers. Students usually say the bottom layer went down first because each new layer had to rest on something. Some say the pencil came last because it goes through every layer. Name these two ideas as tools geologists use, and say that today students will use them, plus fossils, to read millions of years of Earth's history from real rock layers.
Direct Instruction15 minutes
Key words.Sedimentary rock forms when sediment settles in flat layers and hardens. Superposition: in layers that have not been flipped over, each layer is younger than the one below it. Cross-cutting: a fault (a crack where rocks have moved) or a dike (magma that pushed into a crack and cooled) is younger than every layer it cuts. An unconformity is an old erosion surface, a gap in the record where rock was worn away before new layers formed. An index fossil is a fossil of an organism that lived for a short time but over a wide area, so it marks rocks of the same age. A key bed, such as a volcanic ash layer, does the same job. Use Diagram 1 with the second example and Diagram 2 with the third.
Superposition and an unconformity in the Grand Canyon
In the Grand Canyon, flat sedimentary layers about 510 million years old (the Tapeats Sandstone) lie directly on top of tilted, much older rock that formed about 1.7 billion years ago (the Vishnu Schist). The boundary between them is an old erosion surface, called the Great Unconformity.
Result: The lower rock is older (superposition), and the erosion surface shows that rock was worn away before the sandstone formed. The gap is about 1,700 - 510 = 1,190 million years, roughly 1.2 billion years with no rock record at that spot. Strata are a record with missing pages, so geologists combine many places to fill the gaps.
Reading a cross-section: faults, erosion and dikes
In Diagram 1 (an invented cross-section), the fault breaks layers A, B, C and D, but not layer E. The dike cuts through layers A to E, but layer F covers it. A wavy erosion surface runs along the top of D.
Result: Layers A, B, C and D formed first, bottom to top. Then the fault moved them (it cuts them, so it is younger). Then erosion wore down the top, cutting off the fault. Next E was laid down, then the dike pushed through A to E, and last F formed on top. The full order is A, B, C, D, fault, erosion, E, dike, F.
Matching layers between two sites
Diagram 2 shows two invented rock columns 25 km apart. Both have a thin volcanic ash layer and, below it, a limestone with the same kind of trilobite fossils (trilobites were sea animals that lived from about 521 to 252 million years ago). Site 1 also has a shale with ammonite fossils above the ash; Site 2 has gravel there instead.
Result: The ash fell over a wide area in days, so the two ash layers formed at the same time, and the trilobite limestones below them match too. Site 2's shale and siltstone, below its limestone, are older than any layer at Site 1 that can be matched. Putting the columns together gives a longer record than either site alone.
An ash layer as a time marker
About 630,000 years ago, a huge eruption at Yellowstone spread a layer of ash (the Lava Creek ash) across much of the western and central United States. Labs have dated this ash. Geologists find it in lake and river deposits hundreds of kilometers apart.
Result: Wherever the ash is found, the layers below it are older than about 630,000 years and the layers above it are younger, even at sites with no fossils. A significant volcanic eruption becomes a line drawn across the whole region at one moment in time.
Why the time scale has boundaries where it does
In rock layers around the world, the fossils of most ocean species disappear at the same level, which dated ash layers place at about 252 million years ago. The layers above contain many new kinds of fossils.
Result: Geologists put a major boundary of the time scale at that level, between two eras. The time scale is organized by changes in the fossils found in strata, such as the first appearance or the extinction of groups of organisms, and dated layers add the numbers. That is why its units have very different lengths.
Selected major events in Earth's history (published ages, rounded; years before today)
Event
Age
Earth forms
4.6 billion years
Oldest evidence of life: stromatolites (layered mounds built by microbes)
at least 3.5 billion years
Oxygen begins to build up in the air
about 2.4 billion years
Animals with shells and skeletons become common in rock layers
about 539 million years
Appalachian Mountains reach their full height as continents collide
about 300 million years
Largest mass extinction, at the time of huge volcanic eruptions in Siberia
about 252 million years
First dinosaur fossils
about 230 million years
Pangaea begins to split; the Atlantic Ocean basin starts to open
about 200 million years
Asteroid impact; dinosaurs other than birds go extinct
66 million years
Himalayas begin to rise as India collides with Asia
about 50 million years
Earliest fossils of Homo sapiens (modern humans)
about 300,000 years
Last Ice Age ends
about 11,700 years
The largest divisions of the geologic time scale, for reference only (names are not to be memorized)
Division
Time span (millions of years ago)
Precambrian time
4,600 to 539
Paleozoic Era
539 to 252
Mesozoic Era
252 to 66
Cenozoic Era
66 to today
Ask: "Which division is longest? Why might the oldest part have so few divisions?" Help students see that animals with hard parts, which leave many fossils, appear only about 539 million years ago, so earlier rocks have far fewer fossils to mark boundaries.
Guided Practice15 minutes
Pairs use Diagram 1 and Diagram 2 to write a full scientific explanation. A lab has dated the volcanic ash in layer C of Diagram 1 at about 400 million years old (invented value). Pairs answer the question: "What can the rocks in Diagram 1 tell us about when the trilobites in layer B lived and when the fault moved?"
Claim: write one sentence that answers the question.
Evidence: list at least three observations from the diagram (which layers the fault cuts, where the fossils are, where the ash is).
Reasoning: name the rule that links each observation to the claim (superposition, cross-cutting, key bed).
Check your explanation against Diagram 2: what would you need to find at a second site to show that its trilobite layer has the same age?
Model explanation: Claim: the trilobites in layer B lived more than about 400 million years ago, and the fault moved less than about 400 million years ago. Evidence: layer B lies below the ash in layer C; the fault breaks layers A to D, including the ash; layer E is not broken. Reasoning: by superposition, B is older than the ash above it; by cross-cutting, the fault is younger than the ash it breaks, and older than E. A second site would need the same trilobite species, or the same ash layer, to match its layers to these.
Independent Practice10-15 minutes
Clay strata challenge. Each group builds a block of clay strata in secret: at least four layers, one "fault" made by slicing the block with a plastic knife and sliding one side down, and one "dike" made by pushing a pencil-thin roll of a new color through some layers. They may add a top layer after the fault. Groups trade blocks, cut a cross-section with the knife, draw what they see, and write the order of events with the rule that supports each step. Builders check the answer. Safety: use plastic knives only, and wash hands after handling clay.
Closure5 minutes
Return to the warm-up clay block and ask students to restate their reasoning using today's words: superposition and cross-cutting. Exit ticket: "In one or two sentences, explain how rock layers in many different places can be combined into one time scale for the whole Earth." Look for answers that mention matching fossils or ash layers between places and dating some layers to add numbers.
Differentiation Strategies
For Struggling Students
Give a cut-apart set of event cards for Diagram 1 (A, B, C, D, fault, erosion, E, dike, F) to put in order before writing
Provide the frame: "I claim ___. My evidence is ___. This shows ___ because the rule of ___ says ___."
Use the clay block from the warm-up as a model students can touch while reading the diagram
For Advanced Students
Ask students to sketch what Diagram 1 would look like if the fault had moved after layer F formed
Have students explain why an index fossil works best when the organism lived only a short time but spread over a wide area
Ask students to explain why rocks older than about 4 billion years are so rare on Earth, and what other evidence scientists use for Earth's age
Assessment Guidance
What to Look For
Check that explanations have a claim, evidence taken from the strata (not from memory) and reasoning that names a rule. Watch for students who think a fault or dike is as old as the layers it cuts, who order layers by thickness instead of position, or who treat an erosion surface as a layer. When students match sites, check that they use the same fossils or the same ash, not the same rock type alone. Do not grade recall of period names: names in a question are always given.
02
Classroom Activities
3 Activities
1
Rock Column Correlation Cards
20 minGroups of 3-4
Each group gets cards showing rock columns from four invented sites in one region. They match layers between sites using index fossils and an ash layer, then tape the cards into one combined column that is longer than any single site.
Procedure
Lay the four column cards side by side. Color every ash layer gray and every fossil type its own color.
Draw lines between layers that match. Use fossils and ash first; use rock type only as extra support.
Cut and tape the pieces into one combined column, oldest at the bottom.
Mark any place where a layer is missing at one site, and suggest why (erosion, or no sediment settled there).
Discussion Questions
Why is an ash layer a better match than two layers that are both sandstone?
Your combined column is longer than any one site. What does that tell you about how the geologic time scale was built?
One site has a layer with fossils found nowhere else. Where can it go in the combined column, and what evidence would you need?
Modification for Distance Learning
Groups drag the column pieces into place on a shared slide and add text boxes that name the matching evidence.
2
Earth's History on a 4.6-Meter Tape
20 minGroups of 3
Groups make a timeline of Earth's history on 4.6 m of adding-machine tape, at 1 m for every billion years (1 mm for every million years), and place major events from the table on it.
Procedure
Mark "Earth forms" at one end and "today" at the other. Mark every half meter.
Place these events, measuring from "today": oldest evidence of life (3.5 m), oxygen builds up (2.4 m), animals with shells common (53.9 cm), largest mass extinction (25.2 cm), Pangaea begins to split (20 cm), dinosaurs go extinct (6.6 cm).
Shade the part of the tape before animals with shells became common, then measure it.
Discussion Questions
About 4.06 m of the 4.6 m tape comes before animals with shells became common. What does that tell you about where most of Earth's fossils come from?
Why are the recent events so crowded at one end?
Which events on your tape are known from rock strata, and which needed other evidence?
Challenge Variation
Groups add the four largest divisions of the time scale from the reference table as colored bands and explain why the youngest bands are the narrowest yet have the most named subdivisions.
3
Mountains, Ocean Basins and Eruptions in the Rock Record
20 minPairs
Pairs analyze evidence cards about mountain building, ocean basins and a giant volcanic eruption, and write an explanation of how strata record these events.
Evidence Cards
Card 1: In the Rocky Mountains of Colorado, sedimentary layers as young as about 70 million years old are tilted up steeply against the mountains, while layers younger than about 50 million years lie flat on top of them (simplified summary of published findings).
Card 2: Matching rock layers and the same fossil plants and reptiles are found in South America and Africa, on opposite sides of the Atlantic Ocean.
Card 3: Thick salt layers along both coasts of the South Atlantic formed when early seawater dried up in a narrow, young ocean basin (simplified summary).
Card 4: In India, stacks of lava flows more than 2 km thick (the Deccan Traps) were erupted close to 66 million years ago, near the level in the strata where fossils of dinosaurs other than birds end.
Task
For each card, write what event the strata record and whether the evidence gives a relative age, a number of years, or both. Then write one explanation of how strata let geologists place mountain building and ocean basin formation on the time scale.
Discussion Questions
Why does a tilted layer have to be older than the tilting?
How can rock layers on two continents show that an ocean basin opened between them later?
Modification for Distance Learning
Pairs work on a shared document with the four cards and record a two-minute explanation.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: An Invented Cross-Section with a Fault and a Dike
An invented cross-section for practice. Layers A to F are sedimentary, except C, a volcanic ash layer. The red line is a fault: the left side was pushed up. The dark wavy line is an erosion surface. The dark band is a dike of cooled magma. Use the rules of superposition and cross-cutting to put the events in order.
Diagram 2: Matching Layers Between Two Sites
Two invented rock columns 25 km apart, oldest at the bottom. The volcanic ash layer and the limestone with trilobites appear at both sites, so dashed lines join them. Thicknesses differ between sites, and some layers appear at only one site.
04
Homework Assignment
~30 min
MS-ESS1-4 Homework: Explaining Earth's History from Rock Strata
Directions: Every problem gives the data you need; you do not need to remember any names from the time scale. Ages are published values, rounded; cross-sections and data marked invented are made up for practice. Answer each explanation with a claim, evidence from the strata and reasoning that names a rule.
Part 1: Reading Rock Layers (Problems 1-3)
An invented cliff, from bottom to top: granite (cooled magma), then an erosion surface, then sandstone with no fossils, shale with fish fossils, a dark lava flow, and limestone with coral fossils on top. A fault breaks the granite, the sandstone and the shale, but stops at the lava flow. (a) Sketch the cliff. (b) List all the events in order, from oldest to youngest, including the fault and the erosion. (c) For two of your steps, name the rule that supports it.
Three invented sites in one region. Site X, bottom to top: limestone with species-P fossils, ash, sandstone. Site Y: shale, limestone with species-P fossils, ash. Site Z: ash, sandstone, shale with species-Q fossils. (a) Match the layers and draw one combined column. (b) Which layer in the region is the oldest? Which is the youngest? (c) Explain why no single site shows the whole record.
A team counted the kinds of fossils in five layers at one site (invented data). From bottom to top: 48, 51, 46, 9 and 22 kinds. A thin clay layer lies between the third and fourth layers. (a) Make a bar graph. (b) Describe the change. (c) Use the data to explain why geologists might put a boundary of the time scale at the clay layer, and what else they would need to check at other sites.
Part 2: Organizing Earth's History (Problems 4-6)
Squeeze Earth's 4.6-billion-year history into one calendar year, with Earth forming at the first moment of January 1 and today at midnight on December 31. (a) Find the date for each event: oldest evidence of life (3.5 billion years ago), oxygen builds up (2.4 billion), animals with shells common (539 million), first dinosaurs (230 million) and Pangaea begins to split (200 million). (b) In which months does the whole record of animals with shells fall? (c) What does the model show about how the time scale is organized?
Use these data. Folded layers in the Appalachian Mountains contain fossils up to about 300 million years old. Folded layers high in the Himalayas contain sea fossils as young as about 50 million years old. Construct an explanation, with a claim, evidence and reasoning, for which mountain chain began forming first.
The three most recent eras run from 539 to 252 million years ago, from 252 to 66 million years ago, and from 66 million years ago to today. (a) Find the length of each era. (b) Find each one as a percent of the 539 million years. (c) Make a bar graph, and explain what event in the fossil record marks the line between each pair of eras, using the table of major events.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Claim
States a clear claim that answers the question
Claim is present but vague or only partly answers the question
Evidence from Strata
Uses specific observations from the layers, fossils, faults or ash given in the problem
Uses general statements or evidence not from the problem
Reasoning
Names the rule (superposition, cross-cutting, matching fossils or ash) that links evidence to claim
Gives a reason but does not connect it to a rule
Calculations and Models
Dates, lengths, percents and graphs are correct and labeled
Method is right but a value or label is wrong
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Every question gives the data you need, so you do not have to remember any names from the geologic time scale. Ages are published values, rounded; cross-sections marked invented are made up for practice. 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
A road cut shows five flat sedimentary layers that have never been folded or flipped. Which layer is the oldest?
Answer: A
By superposition, each layer was laid down on top of the one below, so the bottom layer is oldest. Choice B confuses thickness with age: a thick layer may form quickly. Choice C is the youngest. Choice D confuses how many fossils a layer holds with when it formed.
Question 2 of 20 · Multiple Choice
In an invented cliff, a dike of cooled magma cuts through layers 1, 2 and 3 (1 at the bottom) but not layer 4 on top. When did the magma push in?
Answer: D
By cross-cutting, the dike is younger than every layer it cuts, so it came after layer 3. It does not cut layer 4, so layer 4 formed later and covered it. Choice A ignores that the dike cuts layer 1. Choice B would mean the dike cuts layer 4 too. Choice C ignores that it also cuts layers 2 and 3.
Question 3 of 20 · Multiple Choice
Which of these fossils would be the best index fossil for matching rock layers of the same age?
Answer: D
A good index fossil lived for a short time but over a wide area, so finding it pins a layer to a narrow span of time in many places. Choice A lived far too long. Choice B lived briefly but in only one lake, so it can't match distant sites. Choice C lived both too long and in too small an area.
Question 4 of 20 · Multiple Choice
In an invented cross-section, a fault breaks layers A, B and C. Layer D lies on top, unbroken. Which statement is supported?
Answer: C
By cross-cutting, the fault is younger than the layers it breaks (A, B and C), and layer D, which is not broken, formed after the fault moved. Choices A and D reverse the rule. Choice B ignores that C had to exist before it could be broken.
Question 5 of 20 · Multiple Choice
Pangaea began to split about 200 million years ago. About what percent of Earth's 4.6-billion-year history has passed since then?
Answer: B
200 ÷ 4,600 ≈ 0.043, or about 4.3%. Choice A treats 200 million as part of 1 billion. Choice C misplaces the decimal point. Choice D is the part of history before the split (100% - 4.3% = 95.7%).
Question 6 of 20 · Multiple Choice
If Earth's 4.6-billion-year history were one calendar year, about when would the dinosaurs (other than birds) go extinct, 66 million years ago?
Answer: A
66 ÷ 4,600 × 365 ≈ 5.2 days before the end of the year, so about December 26. Choice B counts 66 days back instead of 5.2. Choice C puts the event in the last day, which is where events of the last 12 million years or so belong. Choice D is about one day before the end, where an event about 13 million years ago would go.
Question 7 of 20 · Multiple Choice
Two sites 80 km apart each have a thin ash layer from the same eruption. At Site 1, a sandstone lies just below the ash. At Site 2, a shale lies just below it. What can you conclude?
Answer: C
By superposition, each layer below the ash is older than the ash, and the ash marks the same moment at both sites. The data don't show which of the two lower layers is older, so choices A and B go beyond the evidence. Choice D reverses superposition.
Question 8 of 20 · Multiple Choice
At one site, flat rock layers about 150 million years old sit on an erosion surface cut into tilted layers about 400 million years old. About how much time is missing from the record there?
Answer: D
400 - 150 = 250 million years passed between the youngest tilted rock and the oldest flat rock, and no rock from that time is left at this spot. Choice A adds the ages. Choices B and C give one of the ages instead of the gap.
Question 9 of 20 · Multiple Choice
Stromatolites, mounds built by microbes, are found in rock layers about 3.5 billion years old. Fossils of animals with shells first become common in layers about 539 million years old. Which conclusion do these data best support?
Answer: A
3.5 billion - 539 million ≈ 2.96 billion, so microbes left a record about 3 billion years before shelled animals became common. Choice B ignores the 3-billion-year gap. Choice C claims something the strata do not show: there is no evidence for it. Choice D confuses the age of shelled animal fossils with the age of the oldest microbe mounds.
Question 10 of 20 · Multiple Choice
At sites around the world, a thin clay layer rich in the rare metal iridium is dated at 66 million years. Dinosaur fossils other than birds are found below it but never above it. What does this evidence show?
Answer: B
Dinosaur fossils stop at the clay everywhere, so these dinosaurs disappeared at the time it formed, 66 million years ago. Choice A reverses superposition. Choice C ignores the dinosaur fossils below the clay. Choice D ignores that the clay is dated at the same age at every site.
Question 11 of 20 · Multiple Choice
In an invented mountain, a layer with fossils of species that lived 300 million years ago sits on top of a layer with fossils of species that lived 100 million years ago. What is the best explanation?
Answer: C
Mountain building can fold layers so far that some end up upside down, and fossils of known ages reveal it. Choice A goes too far: superposition applies to layers that have not been overturned, and the fossils show these were. Choice B contradicts the given ages. Choice D is not how fossils form.
Question 12 of 20 · Multiple Choice
Limestone with fossils of sea animals is found high in a mountain range. Which explanation do the strata support?
Answer: A
Limestone with sea fossils forms on a sea floor, so these rocks formed underwater and were later raised as the mountains were built, showing the sea came before the mountains. Choice B is not something sea animals can do. Choice C would need far more water than Earth has. Choice D can't explain fossils inside solid rock layers.
Question 13 of 20 · Multiple Choice
A lake lays down about 1 cm of mud every 10 years. A core drilled from the lake bottom has 2.4 m of mud. About how many years does it record?
Answer: C
2.4 m = 240 cm, and 240 × 10 years = 2,400 years. Choice A uses 2.4 m as if it were 2.4 cm and multiplies by 10. Choice B forgets to multiply by 10. Choice D multiplies by 100 instead of 10.
Question 14 of 20 · Multiple Choice
Earth's oldest known rocks are about 4.0 billion years old, yet Earth is about 4.6 billion years old. Which statement best explains the difference?
Answer: C
Plate motions, melting and erosion have destroyed or recycled almost all of Earth's first rocks, so the age of Earth comes from other evidence, such as meteorites and the oldest mineral grains. Choice A contradicts the data. Choice B has no basis. Choice D ignores gaps such as unconformities.
Question 15 of 20 · Short Answer
An invented cross-section, from bottom to top: layer 1 (sandstone), layer 2 (shale with fish fossils), layer 3 (limestone). A dike cuts layers 1 and 2 but stops at an erosion surface on top of layer 2. Layer 3 lies on the erosion surface. Write the order of events and explain each step.
Order: layer 1, layer 2, dike, erosion, layer 3. Layers 1 and 2 formed first, bottom to top (superposition). The dike cuts both, so it is younger than both (cross-cutting). It stops at the erosion surface, so erosion wore down the top of layer 2 and the dike after the dike formed. Layer 3 lies on the erosion surface, so it formed last. The fish in layer 2 lived before the dike and before layer 3 formed.
Question 16 of 20 · Short Answer
Two invented sites. Site A, bottom to top: sandstone, limestone with species-K fossils, ash. Site B, bottom to top: limestone with species-K fossils, ash, shale with species-M fossils. Which layer is the oldest in the region and which is the youngest? Explain with evidence.
Match the limestone with species K and the ash at both sites. Then Site A's sandstone is the oldest, because it lies below the matched limestone. Site B's shale with species-M fossils is the youngest, because it lies above the matched ash. Reasoning: matching fossils and the ash mark the same time at both sites, and superposition orders the layers above and below them.
Question 17 of 20 · Short Answer
On the 4.6-meter tape model (1 mm for every million years), where would the earliest fossils of Homo sapiens (about 300,000 years ago) and the end of the last Ice Age (about 11,700 years ago) go? What does this show about recent events on the time scale?
300,000 years is 0.3 million years, so 0.3 mm from the "today" end. 11,700 years is 0.0117 million years, about 0.01 mm, thinner than the pencil line marking "today." All of human history fits in less than half a millimeter of a 4.6 m tape. Recent events, known in great detail from young layers, take up a tiny part of Earth's history.
Question 18 of 20 · Short Answer
Drilling shows that the oldest sediment layers on the floor of the Atlantic Ocean, just above the volcanic rock of the seafloor, are about 180 million years old near the coasts of North America and northwest Africa. Toward the middle of the ocean, the oldest sediment layers get younger and younger, down to almost zero at the ridge in the middle. Construct an explanation of what these strata show about when and how the Atlantic Ocean basin formed.
Claim: the Atlantic Ocean basin began to form about 180 million years ago and has been growing wider from the middle ever since. Evidence: sediment can only settle on seafloor that already exists, so the oldest sediment at each spot tells when the seafloor there formed. The oldest layers, about 180 million years old, are near the coasts, and they get younger toward the middle ridge. Reasoning: by superposition, the bottom sediment is the oldest at each spot, so the seafloor near the coasts is oldest and new seafloor was added later at the ridge. This fits the table: Pangaea began to split about 200 million years ago, and the ocean basin opened afterward.
Question 19 of 20 · Short Answer
A student says, "Early humans hunted dinosaurs." Use these data to evaluate the claim: the dinosaurs other than birds went extinct 66 million years ago, and the earliest fossils of Homo sapiens are about 300,000 years old.
The claim is not supported. 66,000,000 - 300,000 = 65,700,000, so about 65.7 million years passed between the last of these dinosaurs and the first modern humans. The dinosaur extinction is about 220 times as long ago as the first Homo sapiens fossils (66,000,000 ÷ 300,000 = 220). In strata, dinosaur fossils lie far below any layers with human fossils.
Question 20 of 20 · Short Answer
In Fort Rock Cave in Oregon, archaeologists found woven sandals buried under a layer of ash from the eruption of Mount Mazama, which formed Crater Lake about 7,700 years ago. Using only the ash, what can you say about the age of the sandals? Explain your reasoning.
The sandals are older than about 7,700 years. They lie below the ash, and by superposition anything below a layer was there before the layer fell. The ash is a key bed with a known age, so it gives a limit on the sandals' age even without dating the sandals themselves. (Lab dating of the sandals later showed they are about 9,000-10,000 years old, which fits.)
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-ESS1-4 mean?
MS-ESS1-4 asks middle school students to explain, using evidence from rock layers, how the geologic time scale organizes Earth's 4.6-billion-year history. The code stands for Middle School, Earth and Space Science, core idea 1 (Earth's Place in the Universe), performance expectation 4. The practice is constructing an explanation: a claim backed by evidence from strata and reasoning.
Do students need to memorize the geologic periods for MS-ESS1-4?
No. The Assessment Boundary says assessment does not include recalling the names of specific periods or epochs and events within them. Students should be able to read a time scale or a table that gives the names and use rock evidence to explain how the scale is organized. Tests should give any names they use.
What is the law of superposition?
Superposition is the rule that, in layers that have not been overturned, each layer is younger than the layer below it. Sediment settles on top of what is already there, so the order of layers is the order of time. It is the first tool geologists use to read a cliff or a canyon wall.
What is the difference between relative age and absolute age?
Relative age is the order of events (this layer is older than that one); absolute age is a number of years. MS-ESS1-4 emphasizes relative ages from rock layers and fossils. Absolute ages come from lab dating of some layers, such as volcanic ash, which then gives numbers to the layers above and below. The lab methods are beyond this standard.
How do fossils help build the geologic time scale?
Fossils let geologists match layers of the same age in different places and mark big changes in life. When the same short-lived, widespread species turns up at two sites, those layers formed at about the same time. Where many kinds of fossils disappear or new kinds appear across the world, geologists draw boundaries between units of the time scale.
What is an unconformity in rock layers?
An unconformity is a buried erosion surface: a gap in the rock record where layers were worn away, or never formed, before new layers were laid on top. The Great Unconformity in the Grand Canyon is a famous example. Unconformities are one reason geologists must combine strata from many places to build a complete time scale.
What events can students use for MS-ESS1-4?
The Clarification Statement suggests events from very recent (the last Ice Age, the earliest fossils of Homo sapiens) to very old (the formation of Earth, the earliest evidence of life), plus the formation of mountain chains and ocean basins, the evolution or extinction of organisms, and significant volcanic eruptions. This page uses the Grand Canyon, the Appalachians and Himalayas, the opening of the Atlantic, ash layers and two mass extinctions.
What mistakes do students make when reading rock layers?
Frequent mistakes include ordering layers by thickness, treating a fault or dike as the same age as the layers it cuts, ignoring erosion surfaces, and matching layers between sites only because they are the same rock type. Asking students to name the rule behind each step of their order catches most of these.
Is MS-ESS1-4 Earth science or life science?
It is an Earth and space science standard, but it uses fossils, so it connects closely to life science. It pairs well with MS-LS4-1, which asks students to analyze patterns in the fossil record, and with MS-ESS2-3, which uses fossils and rocks as evidence of plate motions.
What comes after MS-ESS1-4?
In high school, HS-ESS1-6 uses evidence from ancient Earth materials and meteorites to reconstruct Earth's earliest history, and HS-ESS1-5 explains the ages of crustal rocks with plate tectonics. Both use lab dating, which is beyond this standard.
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Related Standards
5 standards
These standards connect to MS-ESS1-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
4-ESS1-1Prerequisite
Use patterns in rock layers and fossils to explain changes in a landscape
Lesson coming soon
3-LS4-1Prerequisite
Analyze fossil data for evidence of past organisms and their environments
Lesson coming soon
Alongside
MS-LS4-1Parallel
Analyze patterns in the fossil record of life's existence, diversity, extinction and change
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