LIFE

Life Reaches Dry Land

~3.22 billion years ago

Archean · Paleoarchean

Long before plants, microbial mats grew on the banks and gravel bars of rivers in what is now South Africa. A few kilometres away, their marine cousins were doing the same on tidal flats, and the chemistry of the two is measurably different: the river mats were running a nitrogen cycle of their own, on land, under an atmosphere with no oxygen.

Why it matters

The colonisation of land is usually told as the story of plants. It opens here instead, more than two and a half billion years earlier, with films of microbes holding wet gravel together.

Dating & uncertainty

Microbial mats draped over river gravels in the Moodies Group of South Africa carry carbon and nitrogen isotope signatures distinct from the marine mats a few kilometres away, which is the argument that they lived out of the sea. Earlier terrestrial life is plausible but has left nothing this clear.

Sources

1. Homann et al. (2018), Nature Geoscience · Microbial life and biogeochemical cycling on land 3,220 million years ago
2. Noffke et al. (2006), Geology · A new window into Early Archean life: microbial mats in Earth's oldest siliciclastic tidal deposits
3. Lenton & Daines (2017), New Phytologist · Matworld: the biogeochemical effects of early life on land

Earth history as one day

06:58:4017 h 1 min before midnight

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