EARTH × CLIMATE

The Two Million Year Meteor Shower

~468 to 466 million years ago

Phanerozoic · Paleozoic · Ordovician

A large asteroid broke apart in the main belt, and the debris has been falling ever since: about a third of all meteorites that reach the Earth today still come from that one body. Swedish limestone of the age holds fossil meteorites in numbers found nowhere else, and the flux of the finest dust rose by three to four orders of magnitude, a thousandfold to ten thousandfold, for more than two million years afterwards.

Why it matters

Nowhere else does the Solar System leave so plain a mark in sedimentary rock. What that mark caused is another matter, and the argument is unusually sharp: one team reads the dust as the shade that tipped the Ordovician into an ice age, another dated the beds precisely and concluded that the breakup and the biological changes around it were simply unrelated.

Dating & uncertaintyDisputed

A zircon date from the meteorite-bearing beds of southern Sweden places the breakup at 468.0 ± 0.3 Ma; other work using extraterrestrial chromite and helium-3 keeps it at 466 Ma. The consequences are disputed more sharply than the date: one team reads the dust as the trigger of an Ordovician ice age, another finds no link to the biological record at all.

Sources

1. Schmitz et al. (2019), Science Advances · An extraterrestrial trigger for the mid-Ordovician ice age: dust from the breakup of the L-chondrite parent body
2. Lindskog et al. (2017), Nature Communications · Refined Ordovician timescale reveals no link between asteroid breakup and biodiversification
3. Schmitz et al. (2023), Estonian Journal of Earth Sciences · The breakup of the L-chondrite parent body 466 Ma and its terrestrial effects: a search for a mid-Ordovician biodiversity event

Earth history as one day

21:31:332 h 28 min before midnight

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