LIFE × EVOLUTION × GENETICS

Our Microbial Ancestor

~2 billion years ago

Proterozoic · Paleoproterozoic · Orosirian

In the mud of the deep sea floor lived an archaeon that no laboratory had ever grown; twelve years of patience were needed to coax it into culture. It is small, slow and fringed with branching arms, and its genome holds a surprise: proteins once thought to belong only to complex cells. Among microbes without a nucleus, its family is the closest kin we have, and the best candidate for the cell that played host in the merger that made us possible.

Why it matters

The cell that swallowed a bacterium is not a creature to be reconstructed from theory alone. Something very like it is still alive in the mud, today.

Dating & uncertainty

The date is the eukaryotic origin itself, which molecular clocks place between about 2.3 and 1.6 Ga. What the Asgard archaea provide is not a date but a relative: the closest living prokaryotic kin of eukaryotes, and a candidate for the host cell.

Sources

1. Zaremba-Niedzwiedzka et al. (2017), Nature · Asgard archaea illuminate the origin of eukaryotic cellular complexity
2. Imachi et al. (2020), Nature · Isolation of an archaeon at the prokaryote-eukaryote interface
3. Schleper et al. (2026), The EMBO Journal · Asgard archaea: have we found our microbial ancestors?

Earth history as one day

13:25:3810 h 34 min before midnight

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