Geologic scale clock / reading edition
Six studies and twelve source-qualified comparisons, with complete labels and local vector diagrams. This edition works without JavaScript.
Open the interactive clock ↗01 / Earth in a day
Compress Earth’s age into one sweep of the dial. The Claron’s introductory marker lies very close to the present. Change to a log ruler to spread out the younger ages.
On a linear Earth clock, the last 50 million years occupy about 1.1% of the sweep.
| Record | Reference value | Meaning and source |
|---|---|---|
| Earth forms | ≈4.54 billion years Rounded marker | Rounded reference estimate; no numerical error band is inferred here. |
| Phanerozoic begins | 538.8 ± 0.6 Ma Reported numerical ± | The ± value is the chart’s reported numerical uncertainty, not a period duration. |
| Cenozoic begins | 66.00 Ma Numerical boundary | No ± value is supplied for this entry; that does not mean zero uncertainty. |
| Claron · introductory marker | ≈50 Ma Rounded marker | A rounded teaching marker from NPS, not the age of every bed or a particular hoodoo. |
What changes when equal distances mean equal ratios?
≈91×
About 91 Claron-marker look-back spans fit into Earth’s age.
4.54 billion ÷ 50 million years
Both are rounded age estimates. A 24-hour Earth analogy puts the marker about 16 minutes before the end.
≈8.4×
The Phanerozoic occupies about 12% of Earth’s age.
02 / Reading the rock
A regional formation summary and a wayside introduction can use different windows. Compare them without turning either window into an error bar.
The Claron windows describe source scope; the Eocene and Paleocene bars describe time intervals.
| Record | Reference value | Meaning and source |
|---|---|---|
| Claron · regional summary | ≈65–35 Ma Source age window | UGS regional age envelope. It does not mean uninterrupted deposition at one site. |
| Claron · wayside summary | ≈60–50 Ma Source age window | NPS wayside summary. Its narrower window is kept separate from the regional envelope. |
| Claron · introductory marker | ≈50 Ma Rounded marker | A rounded teaching marker from NPS, not the age of every bed or a particular hoodoo. |
| Eocene interval | 56–33.9 Ma Time interval | 22.1 million years by subtraction of the pinned numerical boundaries. |
| Paleocene interval | 66–56 Ma Time interval | An interval between two chart boundaries; the shaded width is elapsed time. |
Is this band a span of time, a broad summary, or numerical uncertainty?
≈3×
The broad UGS window spans three times the NPS wayside window.
(65 − 35) ÷ (60 − 50) million years
Different source summaries; neither width is a dating error or evidence of continuous local deposition.
≈2.2×
The Eocene interval is a little over twice as long as the Paleocene.
(56 − 33.9) ÷ (66 − 56) million years
Calculated from pinned chart boundaries; formation names and epoch names are different classifications.
03 / Unequal chapters
Place the Mesozoic boundaries on an actual time ruler. Period names divide history; they do not promise equal durations.
Linear spacing compares differences in years. Log spacing compares ratios of positive ages.
| Record | Reference value | Meaning and source |
|---|---|---|
| Mesozoic interval | 251.902–66 Ma Time interval | A calculated interval; displayed endpoints do not confer exact duration. |
| Triassic begins | 251.902 ± 0.024 Ma Reported numerical ± | A numerical estimate of a boundary; the geological boundary is defined separately. |
| Jurassic begins | 201.4 ± 0.2 Ma Reported numerical ± | Printed precision is retained in the label. The band does not represent a probability density. |
| Cretaceous begins | 143.1 ± 0.6 Ma Reported numerical ± | Pinned to ICS v2024/12; numerical ages can be revised. |
| Cenozoic begins | 66.00 Ma Numerical boundary | No ± value is supplied for this entry; that does not mean zero uncertainty. |
Which gap is larger on each ruler, and why?
≈2.8×
The Mesozoic spans about 2.8 times the Cenozoic to reference present.
(251.902 − 66) ÷ 66 million years
Derived scale comparison, not an exact duration measurement.
≈1.2×
These two periods differ in duration even when a chart gives them equal space.
(201.4 − 143.1) ÷ (251.902 − 201.4)
Period boxes in conventional charts are not necessarily drawn to a time scale.
04 / The recent edge
A few million years still dwarf a century. The log view makes very short reference spans legible without changing their values.
The Holocene reference is 11,700 years before 2000 CE. “Present” here is a reference zero, not a live calendar.
| Record | Reference value | Meaning and source |
|---|---|---|
| Quaternary begins | 2.58 Ma Numerical boundary | Numerical age from the pinned ICS chart. |
| Pleistocene interval | 2.58 Ma–11.7 ka Time interval | Rounded chart coordinates; this is not an exact calendar subtraction. |
| Holocene interval | 11.7 ka–reference present Time interval | The Holocene boundary is referenced to 2000 CE (b2k). This scale does not add years as the calendar advances. |
| One century · reference | 100 years Exact unit benchmark | An exact unit benchmark, not a measured lifespan, local event or erosion rate. |
Where does zero go when the ruler uses logarithms?
≈220×
The Holocene boundary sits within the youngest half-percent of the Quaternary look-back span.
2,580,000 ÷ 11,700 years
Uses rounded source coordinates; the Holocene datum is 2000 CE, not the current year.
≈117×
11,700 years is 117 blocks of 100 years.
11,700 ÷ 100 years
Unit arithmetic using the published b2k reference age; no local human-history claim is made.
05 / A date with room
The bands around these boundaries show the ± values printed by ICS. Open the detail lens to see a band that is too narrow on the broad view.
Reported ± values are not durations. This kit does not assign them a probability distribution or confidence level.
| Record | Reference value | Meaning and source |
|---|---|---|
| Phanerozoic begins | 538.8 ± 0.6 Ma Reported numerical ± | The ± value is the chart’s reported numerical uncertainty, not a period duration. |
| Triassic begins | 251.902 ± 0.024 Ma Reported numerical ± | A numerical estimate of a boundary; the geological boundary is defined separately. |
| Jurassic begins | 201.4 ± 0.2 Ma Reported numerical ± | Printed precision is retained in the label. The band does not represent a probability density. |
| Cretaceous begins | 143.1 ± 0.6 Ma Reported numerical ± | Pinned to ICS v2024/12; numerical ages can be revised. |
Can you see the error band at this scale, or only its point symbol?
≈3×
The printed Cretaceous numerical uncertainty is three times the Jurassic value.
0.6 ÷ 0.2 million years
Compares reported ± values, not the durations of the periods or a common confidence level.
≈25×
The printed ± values differ by a factor of 25.
0.6 ÷ 0.024 million years
A wider numerical band does not mean the boundary itself lasted longer.
06 / Rock & shape
A formation age belongs to the rock record. A column emerges through later weathering and erosion. None of the selected references gives an individual hoodoo a birthday.
An unknown landform age stays unplotted. It is never silently placed at zero or inferred from a regional erosion rate.
| Record | Reference value | Meaning and source |
|---|---|---|
| Claron · regional summary | ≈65–35 Ma Source age window | UGS regional age envelope. It does not mean uninterrupted deposition at one site. |
| Claron · introductory marker | ≈50 Ma Rounded marker | A rounded teaching marker from NPS, not the age of every bed or a particular hoodoo. |
| Holocene interval | 11.7 ka–reference present Time interval | The Holocene boundary is referenced to 2000 CE (b2k). This scale does not add years as the calendar advances. |
| One century · reference | 100 years Exact unit benchmark | An exact unit benchmark, not a measured lifespan, local event or erosion rate. |
| An individual hoodoo’s age | Not assigned Unknown, unplotted | The selected sources do not date a particular column. Unknown is not zero. |
Which question are you asking: when did the rock form, or when did this shape emerge?
≈500,000×
A 50-million-year look-back spans about 500,000 centuries.
50,000,000 ÷ 100 years
The century is only a unit benchmark. This does not date a hoodoo or forecast its survival.
≈4,300×
The rounded Claron marker is about 4,300 Holocene reference spans ago.
50,000,000 ÷ 11,700 years
An age-scale comparison only; rock and landform histories remain separate.
Each diagram uses its own local linear zoom. Compare the printed ± values rather than the apparent widths in separate diagrams.
How the ruler works
A linear ruler places an age at 1 − age / window. A logarithmic ruler uses 1 − log₁₀(age) / log₁₀(window), with a positive lower limit of one year. Older ages sit on the left.
Zero has no logarithm. The log ruler leaves out 0–1 year and shows reference zero separately across a break. Intervals reaching the present end at that separate marker; unknown ages receive no marker.
The dial uses the same transform across a 300° sweep. The optional 24-hour readout is a linear analogy for the selected window. There is no geological-rate simulation.
Keep the source with the number
Primary references checked October 2, 2026. Time-scale values are pinned to ICS v2024/12 so this comparison stays reproducible.
Earth age: approximately 4.54 billion years.
Published or updated 2019-08-02 · checked 2026-10-02
Factual reference only; no source media or prose reproduced.
Pinned numerical boundaries and their printed ± values.
Published or updated 2024-12 · checked 2026-10-02
Factual numerical extraction credited to ICS (Cohen, Finney, Gibbard & Fan, 2013; updated 2024). No chart artwork or colors copied. Newer versions exist; this edition is deliberately pinned.
Holocene/Greenlandian boundary: 11,700 yr b2k, meaning before 2000 CE.
Published or updated 2018-06-19 · checked 2026-10-02
Factual reference only; no source media or prose reproduced.
Regional Claron age summary: about 65–35 million years; ongoing erosion and mass wasting.
Published or updated 2023-05-01 · checked 2026-10-02
Factual reference only. Tyler Knudsen, Survey Notes 55(2). No photographs, maps or source prose reproduced.
Wayside Claron age summary: 50–60 million years.
Published or updated 2024-01-08 · checked 2026-10-02
Factual reference only; no wayside image or source prose reproduced.
Introductory lake/floodplain marker near 50 million years; deposition, uplift and later shaping are separate processes.
Published or updated 2021-09-04 · checked 2026-10-02
Factual reference only. No third-party Lake Claron map or NPS photograph reproduced.
Hoodoos are erosional forms in the Claron Formation, shaped along fractures. This source does not assign individual hoodoo ages.
Published or updated 2024-06-17 · checked 2026-10-02
Factual reference only; no source media or prose reproduced.
