Arithmetic, not a law
The half-billion-year window
Earth is 4.54 billion years old. Divide that by the eight worlds from Io to Earth. You get about 567 million years. That number is arithmetic. Earth’s fossil record is mapped onto those windows below.
How the number is made
Earth’s age (Allègre and colleagues, 1995) divided by eight: Io, Europa, Ganymede, Callisto, Titan, Triton, Mars, Earth. Venus and Mercury are not in that count. They are read as an earlier turn, already spent. The Great Red Spot is not in that count either. Treat it as a ninth, un-emerged body and the window falls near 504 million years. The same division was first posted here on 10 June 2015 as Planetary Shift Every 570 Million Years.
Change the count by one and the window moves by sixty to seventy million years. A number that moves when you change the count is a ruler you chose, not a law of nature.
Earth’s fossil record against the windows
Eight equal windows from Io to Earth. Earth’s dated chapters laid on that ruler. Equal windows are a modeling choice. The dates belong to other people’s papers. The identities — this world as that stage — are the author’s. Those three stay apart. Comparison, not a finding of life on those worlds.
| Stage | World | Earth time | Earth chapter in that window |
|---|---|---|---|
| 1 | Io | 4.54–3.97 Ga | Hadean. Crust forming. Possible transient water by ~4.4–4.0 Ga. No agreed biosphere. |
| 2 | Europa | 3.97–3.40 Ga | Early Archean. Stromatolites and microfossils most workers will defend, ~3.7–3.5 Ga. |
| 3 | Ganymede | 3.40–2.84 Ga | Mid-Archean. Microbial communities; oxygenic photosynthesis may be originating in this span. |
| 4 | Callisto | 2.84–2.27 Ga | Late Archean into the Paleoproterozoic. Great Oxidation Event marked near 2.4 Ga. |
| 5 | Titan | 2.27–1.70 Ga | Opens after the oxygen rise, still microbial. Mid-window: first simple multicellular reports (~2.1 Ga); remains contested. |
| 6 | Triton | 1.70–1.14 Ga | Eukaryote microfossils near 1.75–1.65 Ga. Crown-group diversification later in the window. |
| 7 | Mars | 1.14–0.57 Ga | Neoproterozoic. Snowball glaciations, then Ediacaran macrofossils at the window’s end. |
| 8 | Earth | 0.57 Ga–now | Phanerozoic. Cambrian radiation near 541–520 Ma. The only detected biosphere. |
Table 1. 4.54 billion years divided by eight living worlds. Column four is Earth’s record, not a caption for the body.