Earth Systems Science · Module 5

How much time is in a cliff, and how fast can we spend it?

A few metres of cliff can hold millions of years. People can use up coal, oil, and groundwater in decades.

These slides teach both clocks: how to read deep time, and how to measure our use.

Start → Jump to my project Formula sheet
Two clocks: a cliff that took millions of years, and wells that empty in decades A cliff cross-section, not to scale. From the top down: limestone, a thin volcanic ash bed whose crystals can be dated, shale with shells, and sandstone, all lying flat. Under a wavy unconformity lie older tilted layers, cut by a dike that stops at the unconformity. The oldest rock is at the bottom. On the right is the fast clock: an oil well pumps oil that took millions of years to form, and a water well draws groundwater. People can use both up in decades. SLOW CLOCK layers pile up over millions of years limestone ash bed · its crystals date it shale with shells sandstone unconformity: missing time dike: younger than the layers it cuts oldest FAST CLOCK people use it up in decades groundwater oil oil took millions of years to form not to scale
Read the cliff from the bottom up. Every cut and every gap is part of the story.

Start here · The big picture

Read the slow clock, then measure the fast one

Four parts of Module 5, from the rock record to human use Four panels joined by arrows. Part 1, Layer Detectives, reads the order of rock layers and fossils. Part 2, Time Keepers, puts numbers on that order with half-lives. Part 3, Aquifer Lab, compares how fast resources form with how fast we use them. Part 4, Footprint Lab, measures the marks that use leaves on land, air, and energy. An arrow underneath runs from the slow clock of the rock record to the fast clock of human use. Read the record Part 1 Layer Detectives Put numbers on time Part 2 Time Keepers Resources and rates Part 3 Aquifer Lab Human footprint Part 4 Footprint Lab slow clock: the rock record fast clock: human use

Two clocks, four parts, one museum.

Your team leads one part and teaches it. Your exhibit needs all four.

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Part 1 · Layer Detectives lead this part

Reading the rock record

  • Put layers, cuts, and gaps in order.
  • Explain why most living things never become fossils.
  • Match far-apart layers with index fossils.
  • Bracket an age between two dated layers.
A layered cliff with fossils, a dike, and a buried erosion surfaceA cliff of layers. A top layer, a fossil-bearing layer and a sandstone layer sit on a wavy buried erosion surface, which cuts across tilted older layers below. A dike cuts up through the tilted layers and stops at the erosion surface.

Part 1 · Key idea · Reading layers in order

In an undisturbed stack, the bottom layer formed first

Layers settle one on top of another Three snapshots of a tank of water. First, sand settles to the bottom. Next, mud settles on top of the sand. Last, shells settle on top of the mud. The finished stack has the oldest layer, sand, at the bottom and the youngest layer, shells, at the top. 1 · sand settles 2 · mud on top 3 · shells last youngest ↑ oldest ↓ time

Superposition: in a stack nobody has tilted, flipped, or broken, each layer is younger than the one under it.

It gives you order, not years.

Deep Time MuseumLead visitors through your era from the bottom layer up.

Part 1 · Key idea

Layers start flat, so a tilt came later

Flat layers, then a tilt, then a new flat layer Three snapshots. First, sandstone, shale, and limestone are laid down flat. Next, the stack is tilted about 30 degrees and its top is worn down flat by erosion. Last, a volcanic ash layer settles flat across the tilted, worn-down layers. The flat ash proves the tilting and erosion happened before it. 1 · laid down flat 2 · tilted, then eroded flat ash on top 3 · new layer, flat The line under the ash is an angular unconformity.

Original horizontality: sediment settles in flat sheets. Layers you find tilted or folded were moved after they formed.

So the tilt is its own, later event on your timeline.

Deep-Time Column labInvestigation 1: tilt three layers, erode, then lay ash flat on top.

Part 1 · Key idea

Whatever cuts a rock is younger than that rock

A sealed dike and an unsealed dike Two cross-sections of layers A, B, and C. Left: a dike cuts A, B, and C and is cut off flat by an erosion surface; layer D lies across the top of it. D seals the dike, so D is younger than the dike. Right: a dike rises through A and tapers to a point inside B. Layer C above is not cut, but nothing seals the dike, so this picture alone cannot tell whether C formed before or after the dike. DCBA dike Sealed dike stops flat at D's base D is younger than the dike CBA dike tip Not sealed dike dies out inside B C's order is unknown here

Cross-cutting: a dike (a sheet of cooled magma), a fault, or an erosion surface is younger than every layer it cuts.

A layer above is younger only if it seals the cut: the dike stops flat at that layer's base.

Part 1 · Key idea

An unconformity is missing time

The Great Unconformity in Grand Canyon A Grand Canyon wall, not to scale. At the bottom are the Vishnu Basement Rocks, metamorphic rock about 1.8 billion years old with steep bands. Above a wavy surface called the Great Unconformity sit flat layered Paleozoic rocks, up to the Kaibab Formation at the rim, 270 million years old. A bracket at the unconformity shows about 1.2 billion years of missing record at Granite Gorge, about a quarter of Earth's history. Kaibab Formation · 270 million years layered Paleozoic rocks Tonto Group sandstone Vishnu Basement Rocks about 1.8 billion years Great Unconformity ≈ 1.2 billion years missing ≈ 25% of Earth's history, in a surface with no thickness not to scale · Granite Gorge

An unconformity is a buried erosion surface: rock was worn away, or never laid down, before new layers covered it.

It has no thickness. In Grand Canyon one hides about 1.2 billion years.

Exhibit hallShow your era's gaps. Never smooth them over.

Part 1 · Key idea

A piece inside a rock is older than the rock

Two kinds of inclusions Left: granite worn down at the surface, then covered by sandstone whose bottom holds rounded granite pebbles. The pebbles are older than the sandstone. Right: magma pushed up through layered rock and swallowed chunks of it. The chunks are older than the cooled magma around them. sandstone (younger) granite (older) Pebbles in sandstone the pebbles came first magma (younger) Chunks in magma the chunks came first

An inclusion is a piece of one rock trapped inside another.

The piece had to exist first, so it is older than the rock around it.

Magma that swallows chunks of wall rock is younger than that wall rock.

Part 1 · Worked example · Practice Gym skill

Put seven events in order

Layers A to D with a dike, a fault, and an eroded top Layers A at the bottom up to D at the top. A dike cuts A and B and stops flat at the base of C. A fault offsets A, B, and C, dropping the right side, and D lies across the fault unbroken. The top of D is a wavy erosion surface. DCBA CBA dike fault erosion surface The dike's flat top is C's base: C seals it.
Layers
A (bottom), B, C, D (top)
Dike
cuts A and B; stops flat at C's base
Fault
offsets A, B, C; D covers it unbroken
Top
D is worn down by erosion
  1. SuperpositionLayers in order: A, B, C, D.
  2. DikeIt cuts B, and C seals it: after B, before C.
  3. FaultIt cuts C, and D seals it: after C, before D.
  4. ErosionIt cuts the top of D, so it comes last.
Answer

A, B, dike, C, fault, D, erosion. Check: each cut sits after everything it cuts and before whatever seals it.

Practice Gym skill “Relative dating with cross-cutting relations” (classroom generator): a feature visibly truncated and sealed by the base of a layer formed before that layer; not crossing a layer alone would not show this. Rule: NPS, Cross-cutting Relationships.

Part 1 · Key idea · How fossils form

Most living things never become fossils

Two paths after an animal dies Top row, a shallow sea: a clam dies on the sea floor, mud buries it quickly, and its hard shell is preserved in rock as a fossil. Bottom row, dry land: a small animal dies on the ground, scavengers and decay break it apart, and nothing is left to fossilize. HARD PARTS + FAST BURIAL clam dies mud buries it fast fossil shell SOFT BODY ON DRY LAND animal dies eaten, rots no fossil

A fossil is preserved evidence of past life: a shell, bone, print, or track.

Hard parts and fast burial help. Soft bodies left on land usually rot or get eaten.

So most living things never become fossils, and the record has gaps.

Part 1 · Key idea · Index fossils

Fossils appear in the same order everywhere

How long five fossil groups lasted A range chart from 550 million years ago on the left to today on the right, using the Deep-Time Column lab's rounded teaching ranges. Trilobite group: 521 to 252 million years ago, a 269-million-year span. Graptoloid group: 478 to 419, 59 million years. Ammonoid group: 409 to 66, 343 million years. Fusulinid group: 323 to 252, 71 million years. Nummulites: 56 to 34, 22 million years. The shorter the range, the more precisely the fossil dates a layer. 5004003002001000 millions of years ago (Ma) Trilobite groupGraptoloid groupAmmonoid groupFusulinid groupNummulites 269 Myr59 Myr343 Myr71 Myr22 Myr: sharpest clock Deep-Time Column lab rounded teaching ranges; single species give tighter ones.

Faunal succession: life changed in one direction, so fossil kinds appear in the same order everywhere.

An index fossil lived a short time but spread widely. The shorter its range, the sharper the date it gives.

Part 1 · Key idea

Match layers by fossils and age, not by thickness

Two measured sections 30 kilometres apart, tied by fossils Section A, drawn to physical thickness, from the bottom: limestone 505 to 485 Ma with trilobites, 44 units thick; shale 468 to 448 Ma with graptoloids and trilobites, 76 units; limestone 336 to 320 Ma with fusulinids, 38 units; shale 160 to 145 Ma with ammonoids, 68 units; limestone 55 to 45 Ma with Nummulites, 34 units. Section B: sandstone 472 to 452 Ma with graptoloids and trilobites, 34 units; limestone 334 to 319 Ma with fusulinids, 82 units; sandstone 158 to 143 Ma with ammonoids, 45 units. Three tie lines join layers that share a fossil and have overlapping age windows, even though their thicknesses differ. Section A Section B 30 km apart 505–485468–448336–320160–14555–45 472–452334–319158–143 T G T F A N G T F A T trilobite · G graptoloid · F fusulinid · A ammonoid · N Nummulites Ages in Ma. Height = thickness, not time. Deep-Time Column lab sections.

Correlation means showing that layers in two places are the same age.

A tie line needs a shared fossil and age windows that overlap. Tied layers can differ in thickness: 76 units here, 34 there.

Sections and tie rule: Deep-Time Column lab, Fossils scene, Correlation mode (classroom data). Same fossils, same age: USGS, Fossil Succession.

Part 1 · Key idea · Past environments

Fossils also tell you what the place was like

Three settings and the fossils they leave Three panels. A shallow sea leaves limestone packed with shells. A river floodplain leaves mud with bones and leaves. A swamp forest leaves coal with fern prints. Shallow sea shells in limestone River floodplain bones, leaves in mud coal Swamp forest fern prints, coal

The kind of fossil records the setting, not just the time.

A layer packed with shells formed under the sea. Coal with fern prints formed in a swamp forest.

Exhibit hallPair every “when” with a “where” your fossils support.

Part 1 · Worked example · Layer Detectives' calculation

How old is the dike, and how big is the gap?

A dike between two dated ash beds Left, a cliff from the bottom up: sandstone, an ash bed dated 62 Ma, shale, a wavy erosion surface, and an ash bed dated 48 Ma. A dike cuts the sandstone, the lower ash, and the shale and is cut off at the erosion surface. Right, a time bar: the dike must fall between 62 and 48 Ma, a window 14 million years wide, and the erosion gap fits inside that same window. ash · 48 Ma shale ash · 62 Ma sandstone dike erosion surface cuts the dike 44 Ma66 Ma 48 Ma (seals) 62 Ma (cut) dike in here window 14 Myr older ↓
Stack
sandstone, ash 62 Ma, shale, erosion surface, ash 48 Ma
Dike
cuts the lower three; ends at the erosion surface
  1. Older limitIt cuts the 62 Ma ash: younger than 62 Ma.
  2. Younger limitThe 48 Ma ash seals it: older than 48 Ma.
  3. Width62 − 48 = 14 million years.
  4. The gapErosion fell inside the same window: under 14 million years.
Answer

Dike: 62 to 48 Ma, a 14 Myr bracket. Gap: under 14 Myr. Check: the dike lies between the two ashes, and so does its age.

Layer Detectives' calculation; Practice Gym skill “Bracketing an intrusion between dated ashes” (classroom generator). Bracketing: USGS.

Part 1 · Worked example · Layer Detectives' calculation

When could two far-apart layers both have formed?

Overlap of two age windows A time line from 480 Ma on the left to 440 Ma on the right. The Section A shale spans 468 to 448 Ma. The Section B sandstone spans 472 to 452 Ma. The two bars overlap from 468 to 452 Ma, a shared window 16 million years wide. 480470460450440 Ma older younger Section A shale · 468–448 Section B sandstone · 472–452 shared: 468–452 · 16 Myr
Section A shale
468 to 448 Ma
Section B sandstone
472 to 452 Ma
  1. Older edgeThe overlap starts at the younger of the two old ages: 468 Ma.
  2. Younger edgeIt ends at the older of the two young ages: 452 Ma.
  3. Width468 − 452 = 16 million years.
Answer

Shared window: 468 to 452 Ma, 16 million years wide. Check: it fits inside both layers' windows.

Layer Detectives' team calculation; layer windows from the Deep-Time Column lab, Fossils scene (classroom data). In Ma, a bigger number is older.

Part 1 · Common mistakes

Three rock-record mistakes that cost points

A thrust fault stacks older rock on topThree bands: older rock on top, pushed along a thrust fault over younger rock, which lies on older rock. older (pushed up)youngerolder
✗ Mistake

“The deepest layer is always the oldest.”

✓ Fix

Only in an undisturbed stack. Folds and thrust faults can put older rock on top.

A dike that tapers out is not sealedA dike rises through two layers and tapers to a point below layer C, which nothing seals. C tip, no seal
✗ Mistake

“The dike stops below C, so C is younger.”

✓ Fix

Only if C seals it, with the dike cut off flat at C's base. Dikes can just taper out.

A broad fossil group dates looselyThe trilobite group's bar spans 269 million years; the Nummulites bar spans 22 million years. trilobite group · 269 Myr Nummulites · 22 Myr
✗ Mistake

“Both layers hold trilobites, so they are the same age.”

✓ Fix

The group spans 269 million years. Use a short-lived species and overlapping age windows.

Overturned and thrust stacks: Module 5 trap card. Fossil ranges: Deep-Time Column lab (classroom teaching values).

Part 1 · Check yourself

Your turn: when did the fault form?

Layers A to E with a fault Five layers, A at the bottom to E at the top. A fault offsets A, B, and C. It is cut off flat at the base of D, and D and E lie across it unbroken. EDCBA fault D lies across the fault unbroken.

A fault cuts A, B, and C and stops flat at D's base. How many layers existed when it formed?

Show the answer

B, 3. The fault cuts A, B, and C, so all three were already there. D seals it, so D and E came later. A forgets that C was cut. C counts D, which only covers the fault. D counts every layer.

Part 2 · Time Keepers lead this part

Putting numbers on time

  • Find an age from the fraction of parent atoms left.
  • Explain what a date needs before you trust it.
  • Build Earth's history to scale.
  • Place the five mass extinctions on the time line.
Parent atoms halving, one half-life at a timeFive bars, each half as tall as the one before, labelled 1, ½, ¼, ⅛ and 1/16: the fraction of parent atoms left after each half-life. 1½¼⅛1/16

Part 2 · Key idea · Radiometric dating and half-life

Each half-life, half of the parent atoms left decay

Sixteen atoms through four half-lives Five grids of 16 atoms. At the start all 16 are parent atoms. After one half-life 8 are parent and 8 are daughter. After two, 4 parent. After three, 2 parent. After four, 1 parent and 15 daughter. The parent fraction goes 1, 1/2, 1/4, 1/8, 1/16. start1 half-life234 11/21/41/81/16 fraction of parent atoms left parent atom daughter atom Each step costs the same time: one half-life.

Unstable parent atoms decay into stable daughter atoms at a steady rate.

A half-life is the time for half of the parent atoms that are left to decay.

Each halving costs one whole half-life.

Part 2 · Key idea

Decay never pauses between half-lives

The decay curve is smooth A smooth curve of the fraction of parent left against half-lives elapsed, from 1 at zero down through 0.5 at one half-life, 0.25 at two, 0.125 at three, and 0.0625 at four. Two in-between points are marked: half a half-life leaves 0.707, and 1.74 half-lives leaves 0.30. 10.750.50.250 01234 half-lives elapsed (t ÷ T) parent left ½ half-life → 0.707 left 1.74 half-lives → 0.30 left

The clock runs smoothly, so an age can be 1.74 half-lives, not just 1 or 2.

After half a half-life, 0.707 of the parent is left, not 0.75.

Any fractiont = T × log₂(N₀ ÷ N). N₀ is the parent at the start; N is the parent now.

Part 2 · Key idea

A date is only as good as its closed system

A closed crystal and a leaky crystal Left: a sealed crystal holds its parent and daughter atoms, so their ratio gives a true age since the crystal formed and cooled. Right: a cracked crystal is losing daughter atoms through cracks. With daughter atoms missing, the clock reads too young. Closed nothing got in or out age is trustworthy Leaky daughter atoms escaped age reads too young parent daughter

Radiometric dating reads the parent and daughter atoms in a crystal to give an age in years.

It needs a closed system: no parent or daughter atoms got in or out since the crystal formed and cooled.

Every date carries a ±.

Mostly igneous rocks, such as ash beds, are dated directly; sedimentary layers are bracketed: USGS, Radiometric Time Scale. Closed system and starting daughter: the Deep-Time Column lab's Datability box.

Part 2 · Key idea

Pick a clock whose half-life fits the age

Half-lives of real dating isotopes, on a log scale A log-scale chart of half-lives from USGS. Carbon-14 to nitrogen-14: 5,730 years, useful only for the past 50,000 years. Uranium-235 to lead-207: 704 million years. Potassium-40 to argon-40: 1.25 billion years. Uranium-238 to lead-206: 4.5 billion years. Thorium-232 to lead-208: 14.0 billion years. Markers show the end of the dinosaurs at 66 million years and Earth's age at 4,567 million years. carbon-14 range dinosaurs gone Earth's age Carbon-14 → nitrogen-14 · 5,730 yr Uranium-235 → lead-207 · 704 million yr Potassium-40 → argon-40 · 1.25 billion yr Uranium-238 → lead-206 · 4.5 billion yr Thorium-232 → lead-208 · 14.0 billion yr 1,000 yr1 million1 billion100 billion each tick mark is 1,000 times the one before (log scale)

An isotope is one form of an element. Each radioactive isotope has its own fixed half-life.

Carbon-14 reaches back only 50,000 years: never dinosaurs or most rock.

Classroom clocksPractice Gym and lab half-lives are made-up classroom values, not real isotopes.

Part 2 · Worked example · Time Keepers' calculation

How old is a crystal with 1/8 of its parent left?

Parent fraction against age when the half-life is 1.3 million years Bars for 0, 1, 2, 3, and 4 half-lives with a half-life of 1.3 million years: parent fraction 1 at 0, 1/2 at 1.3, 1/4 at 2.6, 1/8 at 3.9, and 1/16 at 5.2 million years. The 1/8 bar at 3.9 million years is highlighted. Each step adds 1.3 million years. 11/21/41/81/16 01.32.63.95.2 age in millions of years (+1.3 each step)
Half-life T
1.3 million years (classroom value)
Parent left
1/8
  1. Count halvings1 → 1/2 → 1/4 → 1/8: n = 3 half-lives.
  2. Agen × T = 3 × 1.3 Myr = 3.9 Myr.
  3. Daughter1 − 1/8 = 7/8 of the atoms.
  4. RatioD:P = 7/8 ÷ 1/8 = 7:1.
Answer

3.9 million years; D:P = 7:1. Check: 1/16 left would be 5.2 Myr, one more T, not double.

Time Keepers' team calculation; Practice Gym skill “Age from remaining parent fraction” (classroom generator); Deep-Time Column lab, investigation 3 (idealized T = 1.3 Ma, not a named isotope).

Part 2 · Worked example · Practice Gym skill

How many parent atoms are left after 15,000 years?

6,400 parent atoms halving every 5,000 years Bars drawn to scale: 6,400 parent atoms at the start, 3,200 after 5,000 years, 1,600 after 10,000 years, and 800 after 15,000 years. 6,4003,2001,600800 051015 thousands of years
Start
6,400 parent atoms
Half-life
5 thousand years
Time passed
15 thousand years
  1. Half-lives15 ÷ 5 = 3 half-lives.
  2. Halve three times6,400 → 3,200 → 1,600 → 800.
  3. Same thing in one line6,400 × (1/2)³ = 6,400 ÷ 8 = 800.
Answer

800 parent atoms remain. Check: 800 × 8 = 6,400.

Practice Gym skill “Remaining parent after k half-lives” (classroom generator).

Part 2 · Worked example · Practice Gym skill

Read half-lives from a daughter-to-parent ratio

A 15 to 1 ratio is 16 parts, 1 still parent Sixteen squares: fifteen daughter atoms and one parent atom. One sixteenth of the original parent is left, which is four halvings. P 15 daughter : 1 parent 16 parts, all parent at the start 1/16 left = 4 halvings 1 → 1/2 → 1/4→ 1/8 → 1/16 Assumes the crystal held no daughter atoms when it formed.
Ratio D:P
15:1
Assume
no daughter atoms at the start
  1. Total parts15 + 1 = 16 parts, all parent at the start.
  2. Parent left1 part of 16 = 1/16.
  3. Count halvings1 → 1/2 → 1/4 → 1/8 → 1/16: n = 4.
Answer

4 half-lives. Check: 2⁴ − 1 = 15, which matches 15:1.

Practice Gym skill “Daughter-to-parent ratio ↔ half-lives” (classroom generator). The no-starting-daughter assumption: Deep-Time Column lab, radiometric clock box.

Part 2 · Worked example

When the fraction is not a clean half, use log₂

Reading 0.30 parent left off the decay curve The decay curve from 0 to 3 half-lives, with the half-life T equal to 1.3 million years. A dashed line at 0.30 parent left meets the curve at 1.74 half-lives, which is 2.26 million years, between 1.3 and 2.6 million years. 10.50.300.250 01 T2 T3 T 1.3 Myr2.6 Myr3.9 Myr 1.74 T = 2.26 Myr
Half-life T
1.3 million years
Parent left
0.30 (30%)
  1. RatioN₀ ÷ N = 1 ÷ 0.30 = 3.33
  2. Half-livesn = log₂ 3.33 = log 3.33 ÷ log 2 = 1.74
  3. Aget = 1.74 × 1.3 Myr = 2.26 Myr
Answer

About 2.3 million years. Check: 0.30 is between 1/2 and 1/4, so the age is between 1.3 and 2.6 Myr.

Non-whole half-lives: Module 5 slide correction and the Deep-Time Column lab, which treat t ÷ T as continuous. Practice Gym questions use whole halvings only.

Part 2 · Key idea

The time scale is built where the record changes

The Phanerozoic eon and its three eras, to scale The Phanerozoic eon runs from 538.8 million years ago to today. It holds three eras, drawn to scale: the Paleozoic from 538.8 to 251.9 Ma, the Mesozoic from 251.9 to 66.0 Ma, and the Cenozoic from 66.0 Ma to today. Both era boundaries fall at mass extinctions. Before the Phanerozoic come three older eons: Hadean, Archean, and Proterozoic. EON Phanerozoic · 538.8 Ma to now ERAS Paleozoic Mesozoic Cenozoic ↓ 251.9 Ma Permian–Triassic extinction 66.0 Ma end-Cretaceous extinction Older eons (Hadean, Archean, Proterozoic) fill the 4 billion years before.

An eon holds eras, and eras hold periods, like floors holding rooms.

Boundaries sit where the fossils change sharply, often at a mass extinction. They are not evenly spaced.

Part 2 · Key idea · A scaled model of deep time

Drawn to scale, the Precambrian fills 88% of Earth's story

Earth's 4,567 million years on one line, and on one calendar year A proportional bar from Earth's start, 4,567 million years ago, to today. The Precambrian takes 88.2 percent of the bar and the Phanerozoic only 11.8 percent at the right end. Below, the same history squeezed into one calendar year: the Phanerozoic begins on November 18, non-avian dinosaurs vanish on December 26, and our genus, Homo, appears at about 6:38 pm on December 31. TO SCALE Precambrian · 88.2% Phanerozoic · 11.8% 4,567 Ma AS ONE CALENDAR YEAR JFMAMJJASOND Nov 18: Phanerozoic begins Dec 26: dinosaurs vanish Dec 31, 6:38 pm: genus Homo

Draw Earth's 4,567 million years to scale and the Precambrian fills 88.2% of the line.

On a one-year calendar, the Phanerozoic starts November 18, dinosaurs vanish December 26, and our genus arrives at 6:38 pm on December 31.

Ages: ICS chart v2026/06 (4,567 Ma; 538.8 Ma; 66.0 Ma). Genus Homo, 2.8 Ma: Deep-Time Column lab, Time Spiral (teaching value). Calendar: 1 day = 4,567 ÷ 365 = 12.5 million years.

Part 2 · Worked example · Time Keepers' calculation

Build the time line: 1 mm for every million years

A 4.567-metre time line tape A strip of tape drawn to scale with Today at the right end. Earth's start is 4,567 millimetres away, 4.567 metres. The Phanerozoic is the last 538.8 millimetres; the Precambrian is the other 4,028.2 millimetres. Metre marks run along the tape. 0 m1 m2 m3 m4 m Earth's start · 4,567 mm Today Precambrian · 4,028.2 mm Phanerozoic · 538.8 mm
Scale
1 mm = 1 million years
Earth's start
4,567 Ma
Phanerozoic start
538.8 Ma
  1. Whole tape4,567 Myr × 1 mm/Myr = 4,567 mm = 4.567 m
  2. Precambrian4,567 − 538.8 = 4,028.2 mm
  3. Share4,028.2 ÷ 4,567 = 0.882
  4. Percent0.882 × 100 = 88.2%
Answer

Tape: 4.567 m. Precambrian: 4,028.2 mm, 88.2% of it. Check: 4,028.2 + 538.8 = 4,567.

Part 2 · Key idea · Mass extinctions

Five mass extinctions break the fossil record

The five mass extinctions: when, and how many species were lost A chart of species lost against time, from 500 million years ago to today. Ordovician–Silurian, 443 Ma, about 85 percent. Devonian, 374 Ma, about 75 percent. Permian, 250 Ma, more than 95 percent. Triassic, 200 Ma, about 80 percent. Cretaceous, 66 Ma, 78 percent. A dashed line marks the 75 percent threshold. Two of the five end eras: the Permian extinction ends the Paleozoic, and the Cretaceous extinction ends the Mesozoic. 75% line 100%75%50%25%0 species lost ~85%~75%>95%~80%78% 44337425020066 millions of years ago Ordovician–SilurianDevonianPermianTriassicCretaceous ends Paleozoicends Mesozoic

A mass extinction wipes out about 75% of species in less than 2.8 million years.

The record shows five. Two mark era boundaries: Paleozoic to Mesozoic, and Mesozoic to Cenozoic.

Part 2 · Common mistakes

Three dating mistakes that cost points

Half gone takes one whole half-lifeA bar half filled, labelled one half-life, not half of one. 1/2 left = 1 T, not 0.5 T
✗ Mistake

“Half the parent is gone, so it is half a half-life old.”

✓ Fix

Half gone means one whole half-life has passed.

Each halving adds one half-lifeFrom 1/8 at 3.9 million years to 1/16 at 5.2 million years, not 7.8. 1/8 → 3.9 Myr 1/16 → 5.2 Myr ✓ 1/16 → 7.8 Myr ✗
✗ Mistake

“1/16 left is twice as old as 1/8 left.”

✓ Fix

Each halving adds one T. With T = 1.3 Myr: 3.9 → 5.2 Myr, not 7.8.

Carbon-14 cannot reach the dinosaursOn a log time line, carbon-14's 50,000-year reach ends far short of the dinosaurs at 66 million years. C-14: 50,000 yr dinosaurs: 66 million yr
✗ Mistake

“Carbon-14 dated the dinosaur bones.”

✓ Fix

Carbon-14 reaches only 50,000 years. Date ash beds near the bones with uranium or potassium instead.

Part 2 · Check yourself

Your turn: date the clock

A crystal with one quarter of its parent atoms left Four squares: one parent atom and three daughter atoms, so one quarter of the parent is left. The half-life is 1.3 million years. P DDD 1/4 parent left T = 1.3 million years age = ?

A mineral has 1/4 of its parent atoms left. Its half-life is 1.3 million years. How old is its clock?

Show the answer

B, 2.6 million years. 1 → 1/2 → 1/4 is two halvings: 2 × 1.3 = 2.6. A halves T, the “half a half-life” trap. C counts three halvings, which is 1/8. D treats 1/4 as four half-lives.

Part 3 · Aquifer Lab lead this part

Resources and rates

  • Sort resources by rate, not by size.
  • Explain how fuels and metal ores form.
  • Find total use from people × use per person.
  • Predict what overdraft does to a water table.
A tank with water flowing in and outA water tank with an inflow labelled replaced and an outflow labelled used; the water level is what is stored. replaced used

Part 3 · Key idea · Natural resources

Renewable is a rate, not a size

Two stores of a resource: one in balance, one draining Left: a small tank whose inflow arrow is as wide as its outflow arrow, so its level holds steady. It behaves as renewable. Right: a huge tank with a thin dotted inflow that takes millions of years and a wide outflow, so its level falls. It behaves as nonrenewable, however big it is. in: 10 a year out: 10 a year Level holds acts renewable level last year in: over millions of years out: fast Level falls acts nonrenewable, however big

A natural resource is anything from Earth that people use.

A renewable resource is replaced at least as fast as we use it. A nonrenewable resource takes millions of years to form.

The test is a rate, not a size.

Part 3 · Key idea

Fuels and metal ores form in different ways

Fossil fuels from buried remains; metal ores from concentrating processes Left panel, fossil fuels: plant and plankton remains are buried under layers of sediment, then heat and pressure over millions of years turn them into coal, oil, and natural gas. Right panel, metal ores, three ways: hot water flowing through cracks near magma leaves metal-rich veins; heavy minerals settle out inside a cooling magma chamber; and weathering frees heavy grains such as gold that collect in stream gravel, called a placer. FOSSIL FUELS more layers pile on buried remains heat + pressure for millions of years coal, oil, natural gas METAL ORES · THREE WAYS hot-water veins settle in magma stream placers

Fossil fuels (coal, oil, natural gas) form when buried plant and plankton remains are heated and squeezed for millions of years.

Most metal ores form another way: hot water, cooling magma, or weathering and streams gather the metal in one place.

Part 3 · Key idea · Populations and resource use

Total use = people × use per person

Total water use as an area: people times litres per person Two rectangles drawn to scale. Width is the number of people and height is litres per person per day, so area is the town's total daily use. Now: 5,000 people at 400 litres each, 2,000,000 litres a day. Later: 10,000 people at 300 litres each, 3,000,000 litres a day. The later rectangle is shorter but much wider, so its area is one and a half times larger. 2,000,000 L a day 3,000,000 L a day 5,000 people 10,000 people 400 L each 300 L each NOW LATER width = people · height = use per person · area = total use

Total use = number of people × use per person.

More people, or more use each, means a bigger draw on the same aquifer.

Real numbersUSGS: indoor home use is about 80–100 gallons (300–380 L) per person each day.

Part 3 · Worked example · Aquifer Lab's calculation

The town doubles and saves water. Does total use fall?

Daily water use before and after the town grows A bar chart. Now: 2,000,000 litres a day. Later: 3,000,000 litres a day, an increase of 1,000,000 litres a day even though each person uses less. 01 M2 M3 M 2,000,000 3,000,000 +1,000,000 now later litres of water a day (M = million)
Now
5,000 people × 400 L per person a day
Later
10,000 people × 300 L per person a day
  1. Now5,000 × 400 L = 2,000,000 L a day
  2. Later10,000 × 300 L = 3,000,000 L a day
  3. Change3,000,000 − 2,000,000 = 1,000,000 L a day more
Answer

No. Use still grows by 1,000,000 L a day. Check: people × L per person a day gives L a day.

Aquifer Lab's team calculation (classroom numbers). For scale, USGS puts indoor home use at about 300–380 L per person a day.

Part 3 · Key idea · Water and human impacts

Groundwater fills the spaces between grains

An aquifer under the ground, with a well A cross-section, not to scale. Rain soaks into the ground: this is recharge. Near the top the spaces between grains hold air and some water. Below the water table, every space is full of water: this is groundwater. A sand and gravel aquifer lies on a clay layer that water barely moves through. A well reaches down into the aquifer and pumps water up. The Gulf Coast Aquifer under Houston averages about 1,000 feet of fresh water. rain soaks in: recharge spaces hold air and some water water table aquifer: sand and gravel every space full of groundwater clay: water barely moves Gulf Coast Aquifer under campus: ≈ 1,000 ft of fresh water well not to scale

Groundwater fills the spaces between grains below the water table.

An aquifer is a layer that holds and passes enough water to pump. Rain soaking in refills it: recharge.

Under campus: the Gulf Coast Aquifer.

Part 3 · Key idea

Pump faster than recharge and the water table falls

Before and after years of overdraft Left, before: the water table sits high and the ground is level. Right, after years of pumping more than recharge: the water table has dropped into a cone around the well, and the clay layers have squeezed together, so the ground surface has sunk. Around Houston, water levels fell as much as 350 feet and the land sank up to 10 feet. Before water table After overdraft table drops land sinks Houston area: water levels fell as much as 350 ft; the land sank up to 10 ft (about 3 m).

Overdraft is pumping more than recharge. The water table falls, and stored water runs down like a mine.

Around Houston, heavy pumping dropped water levels as much as 350 ft and sank the land up to 10 ft.

Part 3 · Key idea

What spills on the ground can reach your well

A pollution plume moving down to a well A cross-section. At the surface, a leaking fuel tank and fertilized lawn release pollution. Rain carries it straight down to the water table. There it spreads sideways as a plume, and a pumping well pulls the polluted groundwater in. leaking tank fertilized lawn pumping well plume spreads in the groundwater clay water table

Rain carries spilled fuel, lawn fertilizer, and septic leaks down to the water table.

A pumping well pulls nearby groundwater toward it, pollution and all.

Protect the land above an aquifer to protect the water in it.

Part 3 · Worked example · Aquifer Lab's calculation

How long until the aquifer runs dry?

Stored water falling 30 units a year A line chart of water stored in the aquifer against years. It starts at 1,200 units and falls 30 units each year: 900 after 10 years, 600 after 20, 300 after 30, and zero after 40 years. 03006009001,200 010203040 years of pumping dry at 40 years ↘ in 80 · out 110 a year net −30 a year
Recharge
80 units a year
Pumping
110 units a year
Stored now
1,200 units
  1. Net change80 − 110 = −30 units a year
  2. Read the signMinus means overdraft: storage falls every year.
  3. Years left1,200 ÷ 30 = 40 years
Answer

−30 units a year; dry in 40 years at that rate. Check: 40 × 30 = 1,200.

Aquifer Lab's team calculation; Deep-Time Column lab, Resources scene, Aquifer rate test (classroom units, a model, not a forecast).

Part 3 · Worked example · Practice Gym skill

How long will a fuel reserve last at today's use?

A reserve of 1,200 split into yearly slices of 40 A long bar standing for 1,200 billion barrels, cut into 30 equal slices of 40 billion barrels, one for each year at today's use. 1,200 billion barrels one slice = 40 used in one year 30 slices classroom numbers, not a forecast
Reserves R
1,200 billion barrels
Use C
40 billion barrels a year
  1. RuleReserve lifetime = reserves ÷ yearly use
  2. Divide1,200 ÷ 40 = 30 years
Answer

30 years at today's use. Check: 30 × 40 = 1,200. It is a snapshot, not an end date.

Practice Gym skill “Static reserve-lifetime estimate” and Footprint Lab's team calculation (classroom numbers).

Part 3 · Worked example · Deep-Time Column lab model

What if use grows 3% every year?

Total used over time, steady use versus 3 percent growth A chart of total amount used against years. With steady use of 40 a year, the total reaches the 1,200 reserve at 30 years. With use growing 3 percent a year, the curve bends upward and reaches 1,200 at about 21.7 years. reserve: 1,200 06001,200 0102030 years 21.7 yr 30 yr grows 3% a year steady 40
Reserve R
1,200 units
Use now C
40 units a year
Growth g
3% a year = 0.03
  1. Year by yearUse runs 40, then 41.2, then 42.4 ...
  2. Lab rulet = ln(1 + g × R ÷ C) ÷ ln(1 + g)
  3. Plug inln(1 + 0.03 × 30) ÷ ln(1.03) = ln 1.9 ÷ ln 1.03
  4. Evaluate0.642 ÷ 0.0296 = 21.7 years
Answer

About 21.7 years, not 30. Check: growth always makes the reserve run out sooner.

Growth rule: Deep-Time Column lab, Resources scene (a classroom model in classroom units). The Practice Gym asks only whether growth makes the lifetime shorter or longer.

Part 3 · Common mistakes

Three resource mistakes that cost points

A huge tank still drainsA large tank with a thin inflow and a thick outflow. huge store
✗ Mistake

“Our aquifer is huge, so it is renewable.”

✓ Fix

Size doesn't decide it. Pumping faster than recharge drains it like a mine.

A coal seam and an ore vein form differentlyLeft, a flat black coal seam between layers. Right, a gold-colored vein filling a crack. coal: buried ore: hot water
✗ Mistake

“Metal ores form like coal: burial, heat, and pressure.”

✓ Fix

That is fossil fuels. Ores gather from hot water, cooling magma, or weathering.

Reserve lifetime movesA 30-year bar with an arrow showing growth shortening it and another showing new finds lengthening it. 30 yr growth new finds
✗ Mistake

“30 years of reserves means it runs out in 2056.”

✓ Fix

R ÷ C is a snapshot. Growth shortens it; new finds or higher prices can stretch it.

Part 3 · Check yourself

Your turn: when does the aquifer run dry?

An aquifer with recharge 60 and pumping 85 An aquifer holding 1,000 units. Rain recharges it at 60 units a year, and wells pump out 85 units a year. 1,000 units recharge: 60 a year pumping:85 a year

An aquifer holds 1,000 units. Recharge is 60 units a year and pumping is 85. At this rate, how many years until it runs dry?

Show the answer

C, 40 years. Net = 60 − 85 = −25 units a year, and 1,000 ÷ 25 = 40. A ignores recharge (1,000 ÷ 85). B divides by recharge (1,000 ÷ 60). D adds the two rates (1,000 ÷ 145).

Part 4 · Footprint Lab lead this part

The human footprint

  • Compare how fast soil forms with how fast it washes away.
  • Name what dirties the air we breathe.
  • Trace oil from source rock to a trap.
  • Test any practice: is use at or below replacement?
Land, air, and energy: a field, a chimney, and an oil wellGround with a chimney sending up smoke, a pump-jack oil well, and young plants in a field.

Part 4 · Key idea · Land and human impacts

Topsoil takes centuries to build and one storm to lose

Rain on bare soil and on covered soil Two tilted pans of soil get the same rain. Runoff from the bare pan is muddy and settles a thick layer of mud in its cup. Runoff from the pan covered with mulch is nearly clear and settles only a thin layer. Below, a bar shows that one inch of topsoil takes 500 to thousands of years to form. Bare soil thick mud in the cup Covered soil thin mud layer 1 inch of topsoil: 500 to thousands of years One heavy storm on bare ground can strip it in hours.

Topsoil is the dark, living top layer of soil that grows our food.

An inch takes 500 to thousands of years to form. Erosion, soil carried off by water or wind, can strip bare ground in one storm.

Plant cover holds it in place.

Part 4 · Worked example · Footprint Lab's calculation

How long to replace soil one storm washed away?

Five millimetres of soil rebuilt a thin layer at a time Two columns, each 5 millimetres tall. At the task's rate of 0.1 millimetre a year, the column fills in 50 yearly layers: 50 years. At a real-world rate of about 0.05 millimetre a year, it takes 100 years. 0.1 mm a year 50 years ≈ 0.05 mm a year 100 years 5 mm each line = 10 years each line = 10 years
Lost in one storm
5 mm of topsoil
Forms at
0.1 mm a year (task value)
  1. RuleReplacement time = amount lost ÷ rate it forms
  2. Divide5 mm ÷ 0.1 mm a year = 50 years
  3. Real rate1 inch (25.4 mm) per 500 years = 0.05 mm a year
  4. Real time5 ÷ 0.05 = 100 years
Answer

50 years at the task's rate; about 100 years at a real rate. Check: 50 × 0.1 = 5 mm.

Part 4 · Key idea · Air and human impacts

Clean air is a resource, and the worst particles are invisible

A human hair and two sizes of particle, to scale Circles drawn to the same scale. A human hair is about 70 micrometres across. A coarse particle, PM10, is 10 micrometres or smaller. A fine particle, PM2.5, is 2.5 micrometres or smaller, about 30 times narrower than the hair. Sources include engines, power plants, fires, and dust from roads and building sites. human hair ≈ 70 µm across PM10 ≤ 10 µm PM2.5 ≤ 2.5 µm when breathed in reaches deep SOURCES engines · power plants · fires · road and building-site dust to scale · 1 µm = 1 millionth of a metre

Particulate matter is tiny bits of solid or liquid floating in air.

Fine particles, PM2.5, are about 30 times thinner than a hair: invisible, but small enough to breathe in.

Your particle cards catch the bigger ones you can count.

Part 4 · Key idea · Real data

Burning buried carbon is raising CO₂ in the air

Carbon dioxide at Mauna Loa, yearly averages, 1960 to 2025 NOAA annual mean carbon dioxide at Mauna Loa Observatory, in parts per million: 316.91 in 1960, 325.68 in 1970, 338.76 in 1980, 354.45 in 1990, 369.71 in 2000, 390.10 in 2010, 414.21 in 2020, and 427.35 in 2025. The line climbs faster each decade. 300340380420 1960198020002020 CO₂, ppm (parts per million) 316.9 (1960) 427.4 (2025) NOAA Global Monitoring Laboratory, Mauna Loa annual means

Coal and oil hold carbon pulled from the air millions of years ago.

Burning them returns it in decades. At Mauna Loa, CO₂ rose from 317 ppm in 1960 to 427 ppm in 2025.

The carbon cycle moves carbon between air, life, oceans, and rock.

Part 4 · Key idea · Energy resources

Oil and gas collect in a trap under a seal

An oil trap: source, migration, reservoir, and seal A cross-section, not to scale. Deep down, dark organic-rich source rock is heated until it makes oil and gas. They creep upward through porous rock, because they are less dense than the water in it, into an arch of porous sandstone, the reservoir. A tight shale seal caps the arch, so they pool beneath it: gas on top, oil in the middle, water below. A well drills down into the oil. layers above seal: tight shale reservoir: porous sandstone gas oil water source rock: buried remains, heated oil and gas migrate up well

Oil and gas form in buried source rock, then creep upward, because their density is lower than water's.

They collect in porous reservoir rock under a tight seal. Without a seal, they leak away to the surface.

Part 4 · Key idea

Spending deep time on a short budget

How long Earth takes to make a resource versus how long we take to use it A log-scale time line from hours to a billion years. Earth's side: coal and oil take millions to hundreds of millions of years to form; an inch of topsoil takes 500 to thousands of years. People's side: a fuel reserve can be used up in decades, and a storm can strip bare soil in hours. hours1 year1,000 yr1 million1 billion each tick is 1,000 times the one before (log scale) EARTH MAKES IT coal, oil: millions of years 1 inch of topsoil: 500+ years PEOPLE USE IT a fuel reserve: decades bare soil in a storm: hours

A practice is sustainable only when the use rate is at or below the replacement rate.

Wind and sunlight are renewable flows: using them today does not shrink tomorrow's supply.

Anthropocene galleryTurn “sustainable” into a test with numbers and units.

Part 4 · Common mistakes

Three footprint mistakes that cost points

Plants grow in a season; coal takes millions of yearsA plant labelled one season next to a coal seam labelled millions of years. a season millions of years
✗ Mistake

“Coal is renewable because plants still grow.”

✓ Fix

The plants regrow fast; the coal took millions of years. We burn it in decades.

An inch of topsoil takes centuriesA thin topsoil layer labelled 500 or more years per inch. 1 inch: 500+ years
✗ Mistake

“Soil just comes back next season.”

✓ Fix

An inch takes 500 years or more. Bare ground can lose it in storms.

Fine particles are too small to seeA large hair circle beside a tiny PM2.5 dot, about 30 times narrower. hair PM2.5
✗ Mistake

“No smoke means clean air.”

✓ Fix

PM2.5 is about 30 times thinner than a hair: invisible but breathable.

Part 4 · Check yourself

Your turn: how long to rebuild the soil?

Two millimetres of soil lost, rebuilt at 0.05 millimetre a year A ruler shows a 2 millimetre layer of topsoil washed away by one storm. Soil forms at 0.05 millimetre a year. 2 mm lost washed away in one storm soil forms at 0.05 mm a year

Topsoil here forms at 0.05 mm a year. A storm on bare ground strips 2 mm. How long until nature replaces it?

Show the answer

C, 40 years. 2 ÷ 0.05 = 40, and 40 × 0.05 = 2 mm. A multiplies instead of dividing (2 × 0.05). B uses 0.5 mm a year. D slips a decimal place (2 ÷ 0.005).

Part 5 · Every team · Deep Time Museum

Use it in your project

“If your era is the only one a visitor ever sees, what does the rock itself actually license you to claim about it?”

  • Build 6–8 panels on dated evidence.
  • Give every date its method and ±.
  • Argue what our own layer will record.
  • Track every claim you softened.
Open the Deep Time Museum project Project Library
The four Deep Time Museum deliverablesFour cards: an exhibit hall of three panels, a curator's dossier table, an Anthropocene gallery showing a modern layer with pieces of litter, and a field journal. exhibit hall curator's dossier Anthropocene gallery field journal

Use it · Deep Time Museum · Exhibit hall for your era

One panel, one claim, and the evidence that licenses it

One example exhibit panel An example panel for the end of the Cretaceous. A cross-section shows non-avian dinosaur fossils below a thin boundary layer and none above it. Beside it, four labelled boxes: the claim, that non-avian dinosaurs vanished at the end of the Cretaceous; the evidence, their fossils sit below the boundary layer and never above; the date and method, 66.0 million years ago, radiometric, from the international time scale chart; and the limit, that one cliff cannot show how fast it happened. Panel 4 · The end of the Cretaceous no dinosaur fossils dinosaur bones boundary CLAIMEVIDENCEDATE + METHODLIMIT Non-avian dinosaurs vanished atthe end of the Cretaceous. Their fossils sit below theboundary layer, never above. 66.0 Ma · radiometric dates,ICS time scale chart One cliff cannot show howfast it happened.
Turn in
Exhibit hall for your era · Studio Upload, one image page per panel, 6–8 panels
Do
Each panel: one claim, the rock, fossil, or correlation evidence, and a date with its method.
Data
ICS time scale · NPS Grand Canyon · USGS dating
Slides
Order · Index fossils · Bracket · Gaps

Boundary age: ICS chart v2026/06. Dinosaurs at the boundary: Deep-Time Column lab, Time Spiral.

Use it · Deep Time Museum · Curator's evidence dossier

For every panel: method, assumption, uncertainty

Three dossier rows and one claim rewritten to fit its evidence A dossier table with columns for evidence, method, assumption, and uncertainty. Row 1, the dike bracket: relative dating plus two dated ashes; assumes the ash crystals stayed closed systems; 62 to 48 Ma. Row 2, the tie line: relative dating by index fossils; assumes the fossil ranges are right; 468 to 452 Ma. Row 3, the Permian–Triassic boundary: radiometric; assumes closed systems; 251.902 plus or minus 0.024 Ma. Below, a flagged claim, the dike is 55 million years old, is crossed out and rewritten as: the dike formed between 62 and 48 million years ago. EVIDENCEMETHODASSUMES± / WINDOW Dike bracket relative + twodated ashes ash crystals stayedclosed systems 62–48 Ma Tie line relative: indexfossils fossil rangesare right 468–452 Ma P–T boundary radiometric closed systems 251.902± 0.024 Ma FLAGGED: BIGGER THAN ITS EVIDENCE “The dike is 55 million years old.” REWRITTEN TO FIT “The dike formed between 62 and 48 million years ago.”
Turn in
Curator's evidence dossier · Assessment Center, typed, structured
Do
For every panel: the dating method, relative or radiometric, its assumptions, and its ±.
Flag
Any claim bigger than its evidence. Rewrite it to fit.
Slides
Closed system · Bracket · Overlap · Correlation

Use it · Deep Time Museum · Anthropocene closing gallery

Read our own layer as a geologist would in 10,000 years

The present layer on top of the rock record A cliff of older natural layers topped by the present layer. The present layer holds concrete and asphalt, plastic fragments, broiler chicken bones, and landfill trash. Labels give the data: the United States made 292.4 million tons of municipal trash in 2018, and about half went to landfills; broiler chickens now outweigh all other birds on Earth combined. THE PRESENT LAYER older natural layers 1 2 3 1 · concrete and asphalt 2 · plastic fragments 3 · broiler chicken bones all of it: landfill trash U.S. trash, 2018: 292.4 million tons; about 50% to landfills Broiler chickens outweigh all other birds on Earth combined Your criteria: numbers with units, not wishes
Turn in
Anthropocene closing gallery · Assessment Center, typed (HS-ETS1-1)
Do
Argue what our layer will show in 10,000 years, and name the global challenge it records.
Criteria
Measurable: “landfilled share under 40% by 2035,” not “less trash.”
Slides
Two clocks · CO₂ data · Rates

Use it · Deep Time Museum · Field journal

Your journal records every claim you had to soften

One journal entry in seven parts A journal page with the seven parts of a daily entry: header, today's question, raw record, method log, sense-making in progress, dead ends, and handoff. In the sense-making part, the claim that the dike is 55 million years old is crossed out and replaced by: between 62 and 48 million years ago, because two ash beds bracket it. 1 HEADER2 TODAY'S QUESTION3 RAW RECORD4 METHOD LOG5 SENSE-MAKING6 DEAD ENDS7 HANDOFF Day 3 of 7 · Layer Detectives · Data Analyst How old is the dike in our cliff? lower ash 62 Ma · upper ash 48 Ma matched the dike's top to the erosion surface tried to date the dike from its color: no basis The dike is 55 million years old. Between 62 and 48 Ma: two ashes bracket it; no direct date yet. ask: is there a datable mineral in the dike?
Turn in
Field journal · Note Studio, one note titled “Deep Time Museum”
Do
One entry each project day in the seven parts, plus a closing retrospective.
Focus
When evidence makes you cut a sentence, log what you cut and why.
Slides
Closed system · Bracket

Use it · Deep Time Museum · Your team's build

The slides your build and teach-back need

Layer Detectives · fossil columns

Beads with a density above water's sink like shells.

Time Keepers · decay clock and time line

100 coins per shake run; 4.567 m of tape.

Aquifer Lab · aquifer in a tub

Pump, rain, and dye in a clear tub.

Footprint Lab · land, air, energy bench

Rain pans, particle cards, and an oil trap.

Deep-Time ColumnLab readouts are model evidence: “When we changed ___, the ___ changed.” Open the lab

Use it · The rest of the year

Module 5 shows up in your other projects

Houston subsidence: USGS; aquifer: TWDB.

Part 6 · Reference · Formula sheet

Every Module 5 formula, rule, and number on one page

Age in half-lives

age = n × T

n = halvings from 1 to the fraction left. Each halving adds one T. Example

Any fraction

t = T × log₂(N₀ ÷ N)

log₂ x = log x ÷ log 2. Ages need not be whole half-lives. Example

Parent left

N = N₀ × (1/2)ⁿ, n = t ÷ T

Halve once per half-life. Example

Daughter : parent

D:P = (2ⁿ − 1) : 1

Assumes no daughter at the start and a closed system. 7:1 means 3 half-lives. Example

Relative-dating rules

bottom first · flat first · cuts are younger

Inclusions are older; unconformities are missing time. A layer is younger than a cut only if it seals it. Example

Bracket

sealing age < feature < cut age

Younger than what it cuts, older than what seals it. Example

Overlap window

younger old edge → older young edge

468–448 and 472–452 Ma share 468–452 Ma. Example

Scale model

length = age × scale

1 mm per Myr makes 4.567 m. Percent = part ÷ whole × 100. Example

Total use

use = people × use per person

Real indoor use ≈ 300–380 L per person a day (USGS). Example

Net recharge

net = recharge − pumping

Negative means overdraft. Years left = storage ÷ the size of the net loss. Example

Reserve lifetime

years = R ÷ C

A snapshot at today's use, not an end date. Example

With growth (lab model)

t = ln(1 + gR ÷ C) ÷ ln(1 + g)

Deep-Time Column lab only. Always shorter than R ÷ C. Example

Replacement time

years = amount lost ÷ rate formed

Sustainable: use rate ≤ replacement rate. Topsoil ≈ 0.05 mm a year. Example

Real half-lives (USGS)

carbon-14 5,730 yr (only to 50,000 yr) · uranium-235 704 Myr · potassium-40 1.25 Gyr · uranium-238 4.5 Gyr · thorium-232 14.0 Gyr. Slide

Time scale (ICS 2026)

Earth 4,567 Ma · Phanerozoic 538.8 ± 0.6 Ma · Permian–Triassic 251.902 Ma · Cretaceous–Paleogene 66.0 Ma · Quaternary 2.58 Ma. Slide

Part 6 · Reference · Vocabulary

Module 5 words, in plain language

Superposition
In an undisturbed stack, lower layers are older.
Original horizontality
Sediment settles flat; tilting came later.
Cross-cutting
Whatever cuts a rock is younger than it.
Dike
A sheet of cooled magma that cuts across layers.
Unconformity
A buried erosion surface: missing time.
Inclusion
A piece of rock inside another; older than its host.
Fossil
Preserved evidence of past life.
Faunal succession
Fossil kinds appear in the same order everywhere.
Index fossil
Short-lived, widespread fossil that pins an age.
Correlation
Showing layers in two places are the same age.
Isotope
One form of an element, set by its neutron count.
Parent atom
An unstable atom that decays.
Daughter atom
The stable atom a parent decays into.
Half-life
Time for half of the parent atoms left to decay.
Radiometric dating
Age in years from parent and daughter atoms.
Closed system
No parent or daughter atoms got in or out.
Eon
The largest unit of the time scale; holds eras.
Era
A unit inside an eon; holds periods.
Mass extinction
About 75% of species lost in under 2.8 million years.
Natural resource
Anything from Earth that people use.
Renewable resource
Replaced at least as fast as it is used.
Nonrenewable resource
Takes millions of years to form.
Fossil fuel
Coal, oil, or gas made from buried remains.
Groundwater
Water filling the spaces between underground grains.
Water table
The top of the zone full of groundwater.
Aquifer
A layer that holds and passes enough water to pump.
Recharge
Water soaking down to refill an aquifer.
Overdraft
Pumping more than recharge.
Reserve lifetime
Reserves ÷ yearly use: years left at today's rate.
Topsoil
The dark, living top layer of soil.
Erosion
Soil or rock carried off by water, wind, or ice.
Particulate matter
Tiny solid or liquid bits floating in air.
Carbon cycle
Carbon's path between air, life, oceans, and rock.
Source rock
Buried, organic-rich rock that makes oil and gas.
Reservoir rock
Porous rock that holds oil, gas, or water.
Seal
A tight layer that stops oil and gas rising.
Sustainable
Used no faster than it is replaced.

More wordsLook up any term in the Ascent Lexicon.

Part 6 · Reference · Trustworthy data

Real data for your museum, from the people who measure it

Cite itWrite the source, the link, and the date you read it. Live data changes.

Part 6 · Ready for your project?

Three last checks

A dike cuts an ash dated 30 Ma. A layer just under a 22 Ma ash seals it. Tightest age for the dike?

Show the answer

B. It is younger than the 30 Ma ash it cuts and older than the sealing layer, which lies below the 22 Ma ash. A and C each break one limit. D picks the middle, which the evidence does not license.

A crystal's daughter-to-parent ratio is 3:1. How many half-lives have passed?

Show the answer

B. 3 + 1 = 4 parts, so 1/4 of the parent is left: two halvings. A halves the 3. C reads the ratio as the count. D counts the parts.

Which resource is being used as if it were nonrenewable?

Show the answer

C. Pumping beats recharge, so storage falls like a mine. A and D are renewable flows. B is cut more slowly than it regrows.

You made it through Module 5

Now curate your era

Practice the math, test ideas in the Deep-Time Column, then build your exhibit.

Deep Time Museum project Practice Gym · Module 5 Deep-Time Column lab Module 5 page
An hourglass over layered rockAn hourglass, sand running from the top bulb into the bottom, above four layers of rock.