Notes
Tuesday, 29 September 2026 · PlanetaryFormation.com
Fossil windows
Earth’s dated chapters laid on eight equal windows.
Callisto through Earth
Earth’s fossil chapters on eight equal windows.
Earth’s age, 4.54 billion years, divided by the eight worlds from Io to Earth is about 567 million years each. That number is arithmetic. It is not a measured interval. The question is narrower: if those eight equal windows are laid over Earth’s own fossil and climate record, do the famous pins fall in interesting places?
This site reads Io through Mars as consecutive stages of one kind of planet, with living Earth as the present chapter. Venus and Mercury stay out of this count. Only Earth has a detected biosphere. What follows is a comparison. It is not a finding of life on those worlds.
The ordinary view
Life is known on one planet. The dates below belong to other people’s papers: stromatolites and microfossils most workers will defend near 3.7–3.5 billion years ago; the Great Oxidation Event beginning near 2.45–2.33; eukaryote fossils near 1.7; Snowball Earth in the Cryogenian; Ediacaran bodies before the Cambrian radiation near 541–520 million years ago. Nothing below voids that timetable. It asks only where those chapters sit if Earth’s age is cut into eight equal parts.
The ruler
Equal windows are a modeling choice. They are not a heating law and not a transport law. Change the count by one and every boundary moves by sixty to seventy million years. Column four in the table is Earth’s record, not a caption for the moon or planet in column two.
| Stage | World | Earth time | Earth chapter in the window |
|---|---|---|---|
| 1 | Io | 4.54–3.97 Ga | Hadean. No agreed biosphere. |
| 2 | Europa | 3.97–3.40 Ga | Early Archean. First defended life ~3.7–3.5 Ga. |
| 3 | Ganymede | 3.40–2.84 Ga | Mid-Archean. Still microbial. |
| 4 | Callisto | 2.84–2.27 Ga | Great Oxidation Event marked ~2.4 Ga. |
| 5 | Titan | 2.27–1.70 Ga | After the oxygen rise. Disputed simple multicellular pin ~2.1 Ga. |
| 6 | Triton | 1.70–1.14 Ga | Eukaryote microfossils ~1.75–1.65 Ga. |
| 7 | Mars | 1.14–0.57 Ga | Snowball glaciations, then Ediacaran bodies. |
| 8 | Earth | 0.57 Ga–now | Phanerozoic. Cambrian radiation ~541–520 Ma. |
Io, first on the list, is a silicate world whose crust is still being rewritten by lava and sulfur. Earth’s Hadean sits in that window, with no agreed biosphere. Tides are the usual source of Io’s heat. They do not rule out heat from the interior as well. Neither source makes Io a Hadean Earth, and neither puts cells on Io.
Table 1. 4.54 billion years divided by eight living worlds. The last column is Earth’s chapter. It is not a detection on that body.
The two pins that do the work
The tightest match is the living chapter. This window opens at about 568 million years ago. The Cambrian radiation is dated near 541–520. Offset: about 25–30 million years. Ediacaran remains sit on the line behind it. Everything after — the later animal and plant record — sits here because this is the present end of the count, not because the mapping invents it.
The second strong pairing is late Mars time. Sturtian ice about 720–660 million years ago and Marinoan about 650–635 sit in that window. Ediacaran macrofossils about 575–541 sit on the Mars–Earth line. The Neoproterozoic oxygen rise belongs to the same span. Ice, then large soft bodies, then the Cambrian. That is the last window before the living chapter. It is not a report of those bodies on Mars.
| Pin | Window | Fit |
|---|---|---|
| Cambrian ~541 Ma vs Earth start ~568 Ma | Earth | Strong — offset 25–30 Myr |
| Snowball ice + Ediacaran vs late Mars | Mars | Strong — both sit inside the window |
| GOE ~2.45–2.33 Ga vs Callisto/Titan line ~2.27 Ga | Callisto–Titan | Moderate — offset ~60–180 Myr |
| First defended life ~3.5–3.7 Ga vs Europa | Europa | Moderate — sits inside, not at the open |
| Eukaryote fossils ~1.7 Ga vs Triton start ~1.70 Ga | Triton | Moderate — order match, thin record |
| Simple multicellularity ~2.1 Ga vs mid-Titan | Titan | Moderate and disputed |
What would move each pin
A pin is useful only if it can come off the table. Table 3 is that test. The strong pins fail only if the Earth dates themselves move across a window boundary. The moderate pins fail more easily: a later GOE, an older defended cell, or an accepted Franceville animal would rearrange the middle of the ruler without touching Cambrian or Snowball.
| Pin | What would move it off the window | What would not |
|---|---|---|
| Cambrian | A radiation pushed before 600 Ma | A few million years of new dating inside 541–520 |
| Snowball + Ediacaran | Both events dated after 570 Ma | A new name for the same ice |
| GOE | Onset locked after 2.27 Ga, fully inside Titan | Choosing 2.45 vs 2.33 inside Callisto |
| First life | A defended biosphere older than 3.97 Ga | A contested 3.8 Ga claim staying contested |
| Eukaryotes | A well-dated body older than 1.70 Ga | A new microfossil in the same 1.75–1.65 band |
| 2.1 Ga remains | The Franceville pin accepted as animals | Leaving the pin disputed |
The moderate pins
The first dates most workers will defend for life, about 3.7–3.5 billion years ago, sit in the Europa window. Claims older than 3.8 billion years exist and stay contested. Europa is a global ocean under young ice. The analog is an early wet chapter. It does not put cells in that ocean.
The Great Oxidation Event is not one day. Onset estimates run from about 2.45 to 2.33 billion years ago; some records treat the rise as a 200-million-year interval. The Callisto–Titan line is 2.27. If the onset is 2.45, the pin sits late in Callisto, offset about 180 million years. If the onset is 2.33, the offset is about 60 million years. Same order of magnitude either way. Not a hit to the year. Callisto is a quiet ice lid. Titan is the first world in the sequence with nitrogen air, rain, and seas. Earth’s chapter after the oxygen rise is a thicker oxidized surface. Those two sentences stay apart.
Eukaryote microfossils near 1.75–1.65 billion years ago open the Triton window. Reports of simple multicellular remains near 2.1 billion years ago fall mid-Titan and are disputed. Titan’s measured weather is stronger than that pin and must not be made to lean on it.
What this does not detect
It does not report life on any world but Earth. Europa Clipper can measure ocean chemistry; organics are not a cell. Dragonfly can measure Titan’s air and ground; chemistry is not a fossil. Returned Martian samples can date rocks; dates are not identity. JUICE will weigh Ganymede and Callisto; structure is not a biosphere.
What would weaken this
A defended biosphere older than 3.97 billion years would crowd the Io window, which this page leaves empty. A Cambrian radiation pushed back before 600 million years would miss the living-chapter open. A GOE locked after 2.27 billion years would take the oxidation pin off Callisto. Neither result would prove a handoff.
What this page holds
Earth’s own chapters — first defended life, oxygen, nucleated cells, ice and Ediacaran bodies, then the Cambrian — fall near windows this site already uses for other reasons. Two pins are strong. The others are moderate and can move. The number remains arithmetic. This site reads those eight worlds as consecutive stages. The record does not prove the handoff.
Sources
Allègre, C. J., Manhès, G., and Göpel, C. (1995). Age of the Earth, 4.54 billion years.
Luo, G., and colleagues (2016); Ostrander and colleagues (2024). GOE onset near 2.33–2.45 Ga; some records treat the rise as an interval, not a day.
El Albani, A., and colleagues (2010, 2014). Franceville remains near 2.1 Ga; pin disputed.
Porter, S. M., and Riedman, L. A., and related work. Eukaryote fossils near 1.75–1.65 Ga.
Hoffman, P. F., and colleagues (2017). Sturtian and Marinoan intervals.
Wood, R., and colleagues (2019). Cambrian radiation near 541–520 Ma.