LIFE × EARTH

The Largest Reefs Earth Has Had

~390 to 372 million years ago

Phanerozoic · Paleozoic · Devonian

Stromatoporoids, which were sponges, and tabulate corals built reef tracts larger than anything before or since, the Great Barrier Reef included. They were already shrinking before the end, and the extinction at the Frasnian-Famennian boundary finished them. Bacteria took over the reef-building, and the last stromatoporoids hung on in South China for millions of years after the rest were gone.

Why it matters

Coral reefs did not come back for more than twenty million years, the longest gap in the record. That is what an ecosystem costs: not the animals, which can be replaced, but the structure, which has to be rebuilt from nothing by whoever is left.

Dating & uncertainty

Reef area peaked in the Middle Devonian and was already falling through the Frasnian before the extinction at its end. The final stromatoporoid reefs hung on into the latest Devonian in South China, so the collapse was staggered rather than instant.

Sources

1. Copper (2002), Palaeogeography, Palaeoclimatology, Palaeoecology · Reef development at the Frasnian/Famennian mass extinction boundary
2. Yao et al. (2020), Earth-Science Reviews · The longest delay: re-emergence of coral reef ecosystems after the Late Devonian extinctions
3. Liang et al. (2024), Palaeogeography, Palaeoclimatology, Palaeoecology · The last episode of coral-stromatoporoid reef and faunal changes across a Devonian-Carboniferous boundary section of South China

Earth history as one day

21:56:172 h 4 min before midnight

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