LIFE × EVOLUTION

The First Complex Cells

~2.0–1.8 billion years ago

Proterozoic · Paleoproterozoic · Statherian

Until this point, every living thing had been a simple cell, a bacterium or an archaeon. Then a new kind of cell appeared: larger, with a nucleus to hold its genes, an internal skeleton, folded compartments for its chemistry, and the ability to swallow other cells whole. Biologists call it the eukaryotic cell, and it arose only once, from an archaeon and the bacterium it took in. Every animal, plant, fungus and seaweed, everything alive that you can see, is built of these cells and no others; the earliest fossils everyone accepts are around 1.6 billion years old.

Why it matters

Bacteria have run the planet's chemistry for four billion years, and in all that time they never built a body bigger than a mat. Everything bigger came from this new cell, and from it alone.

Dating & uncertainty

Estimates for the last common ancestor of all living eukaryotes range from 2.2 to 1.6 billion years, and the spread comes from the method rather than the rocks: different clock models, different fossil calibrations, and disagreement over which ancient microfossils are eukaryotic at all.

Sources

1. Betts et al. (2018), Nature Ecology & Evolution · Integrated genomic and fossil evidence illuminates life's early evolution and eukaryote origin
2. Mills et al. (2022), Nature Ecology & Evolution · Eukaryogenesis and oxygen in Earth history
3. Parfrey et al. (2011), PNAS · Estimating the timing of early eukaryotic diversification with multigene molecular clocks

Earth history as one day

14:29:049 h 31 min before midnight

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