I read once that we have two sources for proteins:
- Protein that is made in cells
- Protein that is made in labs
However, based on Miller–Urey experiment, it's argued that amino acids can be made from initial Earth's condition, and from this link, it seems that protein-first world is a hypothesis.
Yet if we accept that proteins could be made before cells, then the process that made proteins in the first place is still out there. This means that we should be able to find proteins outside cells or labs in nature.
Do we find protein not of cellular origin in nature?