Convergent evolution doesn't apply to the exact chemicals used in genetic makeup, only to structure which affects function;
Well, here is a question even experts in biology can't answer and probably will not answer before we either find alien life or understand the origin of life. If we assume that life originates from a self replicating lump of chemicals arranged in the correct way, these chemicals are going to need a way to store
information for their function and replication. And if we assume that DNA is the best and one of the only methods for storing information for life forms in environments similar to ours, then the descendants of this proto-organism will end up using DNA very similar to ours (maybe they'll use arsenic, maybe their RNA will be translated in quadruplets instead of triplets but the underlying structure (binary helix, four building blocks) will be the same.) Of course that's a lot of assumptions so I'll agree that this argument is weak.
the Prophecy of Us doesn't sound a lot different than RL religious/spiritual beliefs, and if we didn't know the sci-fi setting we wouldn't jump to that conclusion;
I'll agree that prophets usually word their prophecies in such a way that they are almost always fulfilled, but I do think there is a grain of truth in this prophecy. Time will tell I guess.
it's entirely plausible that chemicals from Terran organisms would have some effect on other organisms, even without significant chemical similarities small-scale (metabolic and similar chemistry, maybe, but convergent evolution has a good argument there);
Caffeine effecting us implies that our nerves and metabolic system function similarly to terrestrial nerves and metabolic systems, although I guess convergent evolution can explain that.
and we really don't know what those four sigils are. Maybe it's just a designation, or maybe our PC is mistaking I for l or something.
Our PC has displayed remarkable intelligence and observational skills, being so good as to see people giving money to other people from the top of a hill. He'd have to be really sleepy to mistake two letters.
And long sequences comprised of only four symbol types can only be DNA or a DNA-equivalent, since if it were anything else it would have either more symbol types (for example if it were describing
codons it would have to use 4^3=64 distinct symbols in a long DNA-like sequence where proteins translate similarly to human proteins) or less symbols (usually when one searches for certain markers like blood type or does ancestral-DNA comparison). I personally can't think of any other occasion in biology where 4 symbols would be used to form long sequences that vary between species.
If they really were the same nucleic acids, why would the four letters be arranged differently?
That's like saying "If I compare an ape and a human, why would their DNA be different?". Sure, there would be some similar sequences concerning production of similar proteins (as is evident from the rat-human comparison I posted earlier) but overall the DNA sequence would be vastly different.
