LIFE × EVOLUTION × CLIMATE

Plants Colonise the Land

~470 million years ago

Phanerozoic · Paleozoic · Ordovician

The first plants to live out of water were small, flat and rootless, closer to a liverwort than to anything with a stem. They are known almost entirely from their spores, scattered by the million through Ordovician rock, and from a few shreds of tissue found in Oman that still hold spores inside their cases. The oldest of them, from Argentina, are 473 to 471 million years old.

Why it matters

The continents were bare rock and microbial crust for four billion years. Green land is younger than the Cambrian animals that preceded it in the sea, and the first fifty million years of it are known only from dust: the plants that made those spores would not appear as recognisable fossils until the Silurian.

Dating & uncertainty

Cryptospores from Argentina at 473 to 471 Ma are the oldest direct trace. Molecular clocks calibrated on them push the origin of land plants back into the Cambrian, well before any fossil, and that gap is unresolved.

Sources

1. Rubinstein et al. (2010), New Phytologist · Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana)
2. Wellman et al. (2003), Nature · Fragments of the earliest land plants
3. Morris et al. (2018), PNAS · The timescale of early land plant evolution
4. Servais et al. (2019), Palaeogeography, Palaeoclimatology, Palaeoecology · Revisiting the Great Ordovician Diversification of land plants

Earth history as one day

21:30:552 h 29 min before midnight

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