EARTH

The Bombardment That May Never Have Happened

~3.9 billion years ago (existence disputed)

Archean · Eoarchean

Rocks brought back from the Moon seemed to record a brief, violent surge of asteroid impacts half a billion years after the planets formed, and textbooks have carried that surge for fifty years. It may be an artefact of the dating method rather than an event.

Why it matters

Few fixtures of deep time are dismantled before our eyes. The reminder is worth keeping: a date can be a property of the instrument that produced it.

Dating & uncertaintyDisputed

Modelling shows that a steadily declining impact rate, with no surge at all, reproduces the same apparent peak once argon is allowed to leak from the crystals being dated. A 2024 comparison of dating methods applied to the same lunar rocks goes further: the hypothesis may not be testable with the samples we hold.

Sources

1. Boehnke & Harrison (2016), PNAS · Illusory Late Heavy Bombardments
2. Hartmann (2019), Geosciences · History of the terminal cataclysm paradigm
3. Harrison et al. (2024), Earth and Planetary Science Letters · A failed search for concordancy across multiple isotopic systems in lunar impactites

Earth history as one day

03:22:5920 h 37 min before midnight

if Earth’s 4.54 billion years were compressed into a single day