LIFE × EVOLUTION

The Ordovician Fills the Sea

~485 to 443 million years ago

Phanerozoic · Paleozoic · Ordovician

The Cambrian settled the body plans; the Ordovician filled the sea with them. Families multiplied several times over, reef building passed from microbes to animals, and plankton with its own predators became a world in itself, stacked above the seafloor rather than on it.

Why it matters

The modern ocean, layered from plankton down through reef to open water, dates from here rather than from the Cambrian. Whether it deserves to be called one event is disputed: diversity climbs at different times on different continents, and on one reading the single global surge is an artefact of pooling databases that are not evenly sampled.

Dating & uncertainty

Whether this is one event or many is actively argued. Diversity rises at different times in different groups and different parts of the world, and one school holds that calling it a single global event is an artefact of pooling databases.

Sources

1. Servais et al. (2010), Palaeogeography, Palaeoclimatology, Palaeoecology · The Great Ordovician Biodiversification Event: the palaeoecological dimension
2. Servais & Harper (2018), Lethaia · The Great Ordovician Biodiversification Event: definition, concept and duration
3. Servais et al. (2021), Paleontological Research · The Great Ordovician Biodiversification Event is not a single event

Earth history as one day

21:26:102 h 34 min before midnight

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