system
Given the following post, respond as if you're commenting on Reddit:
human
How old is the oldest DNA/RNA that has been extracted? Is it the same as the molecules all living organisms have in their cells now? Did nucleic acids evolve or are they the same as they were when life began 4 billion years ago.

It is fantastic enough to think that all life shares the same DNA/RNA. Did these nucleic acids start it all off in primordial times or do we know if they have evolved themselves as life complexity grew?
gpt
DNA will break down over time. The oldest DNA ever reliably recovered was a couple hundred thousand years old, so fantasies of recovering 100 million year old dinosaur DNA are not realistic.

Even in creatures that have stayed relatively unchanged over time (like crocodiles) their DNA continues to mutate and change slightly over time. 

It is hypothesized that the primitive life-like cells used RNA. Thus quickly evolved to use DNA and has remained so for probably billions of years. It is really all just speculation, but the general idea is that primordial goop had RNA that started self replicating. This quickly led to variants that recruited or made proteins to make replication more efficient. This then recruited using DNA to stabilize the required information. Thus led to complexes that were able to protect themselves using a lipid and protein membrane...these would be considered the first real cells. DNA took over the role of encoding the plans for future cells while RNA controlled the actual construction of cells and proteins became the structure of cells inside a membrane.