So, really the question is how many possible ways can you get self replication not how complex is the first example.
You will need a huge amount of self-replicating chromosomes between 180 and 160 basis to make up for the increased size - it's known that self replication is not common, but I don't think we know that to a 10^-22 certainty either, so all that can still be wrong.
Anyway, there isn't a lot to argue about self-replicating on that context. It means that this chromosome is able to create copies of itself in a RNA-rich ocean. It can require light for that, or a big thermal gradient, but not both. The exact conditions of the ocean are, AFAIK, unknown, but things like your example do not fit.
However, life showed up on earth at a very early stage which suggest it has a relatively high probability over a planets lifespan. Without other information to go on earth is probably topical and life generally shows up within the first 500 million years watter shows up.
> However, life showed up on earth at a very early stage which suggest it has a relatively high probability over a planets lifespan.
1 - That's a good explanation. As good as any other.
2 - Alternatively, life's appearance depends on something that only existed in that short timespan (both light and a big temperature gradient at the same place is a great candidate).
3 - Or life requires some time to evolve so intelligence can only appear on planets that life was early.
4 - Or, you can mix #2 and #3 at varying amounts.
Nucleic acid replication involve them being both dual and single base sequences on different stages. So the difference between "bases" and "base pairs" is meaningless.
Now, 36 basis is extremely short. I don't think anybody believes there's anything that size that able to reproduce. Last time I checked, the smallest known self-reproducing chromosome had around 160 basis. That is, it had a probability of ~10^-96 of appearing between all 160 basis chromosomes. (And remember, there are ~10^80 atoms on the observable Universe...)