[gilleain]

I've no idea about fossils, but I suspect macromolecules like ribosomes or DNA might have too small features to fossilise?

From https://en.wikipedia.org/wiki/Microfossil

> A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size

Which is a bit vague, but 0.001mm is 1000nm while a ribosome is in the range of 20-30 nm diameter. So a whole ribosome is around a 1/50 below the lower end of the microfossil range.

Even though DNA can be a lot longer (1000 base pairs is 3.4 nm - I think? - so a hundred kilobases would be 300-400 nm) the atomic features are too small to fossilise would be my guess.