DNA and RNA use three of the same nucleotides. Adenine (A), cytosine (C), and guanine (G). DNA uses thymine (T) as its fourth base. RNA uses the very similar uracil (U). Get it?
DNA has one less hydroxyl group on its pentose sugar (deoxyribose) than RNA (ribose), which generally makes the backbone of DNA more stable than that of RNA. DNA is generally found in a double helix, while RNA is generally in much more flexible single strands. In short, you want to date RNA, but you want to marry DNA.
This is also why scientifically accurate pick-up lines do not work.
*I’m pretty sure that this is the first (and possibly only) time I have posted a cat picture on the internet.
The Finch and Pea 