Era· The columns of time
Eoarchean
4.03 Ga → 3.6 Ga
The dawn era, and the first four hundred million years for which any rock survives at all. What it holds is thin, contested, and among the most important evidence there is.
What the evidence shows
Its whole record is a handful of outcrops in Greenland, Canada and Australia, metamorphosed almost past reading. In them sit the oldest claims for life: stromatolites one to four centimetres high at Isua, small layered mounds that microbes are thought to have raised, at 3.7 billion years, and graphite in Labrador rock of 3.95 billion years whose carbon is sorted the way living cells sort it. Both are disputed, and for the same reason: at this degree of alteration, what life leaves and what deformation makes can look the same.
Bounds and conventions
An era whose beginning is set by what has survived rather than by what happened, and whose end, 3.6 billion years, is a round number with no event attached. The claims it contains are the most consequential and the least secure on the whole chart.
Sources
- Cohen, K. M., Finney, S. C., Gibbard, P. L., Fan, J.-X. (2013). The ICS International Chronostratigraphic Chart. Episodes 36(3), 199–204, mise à jour continue, voir Cohen et al. (2025), Episodes.
- Nutman et al. (2016), Nature · Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures
- Tashiro et al. (2017), Nature · Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada