LIFE × GENETICS

One Molecule Doing Two Jobs

~4.1 billion years ago (a stage, not a date)

Hadean

In living things the work is divided: DNA stores the instructions, proteins carry them out. Neither can be made without the other, a circle that makes the starting point hard to explain. RNA does both jobs at once, excelling at neither. The suspicion is that it did both first, and the evidence sits inside our own cells: several of the helper molecules that metabolism depends on are recognisable fragments of RNA machinery, left in place.

Why it matters

No one has yet offered a more concrete answer to the hardest question in biology: how ordinary chemistry became a process that copies itself.

Dating & uncertaintyDisputed

No rock records this stage. The date is squeezed between the arrival of liquid water on one side and the last common ancestor on the other. Whether RNA truly came first, or appeared at the same time as DNA and short proteins, is argued hard, and recent laboratory work builds both kinds of component under the same conditions.

Sources

1. Powner et al. (2009), Nature · Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions
2. Xu et al. (2020), Nature · Selective prebiotic formation of RNA pyrimidine and DNA purine nucleosides
3. Goldman & Kaçar (2021), Journal of Molecular Evolution · Cofactors are remnants of life's origin and early evolution

Earth history as one day

02:19:3321 h 40 min before midnight

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