Why RNA not DNA was the first living molecules?

Why RNA not DNA was the first living molecules?

Enzyme activities of RNA molecules are constantly being discovered, but no enzymatic activity has ever been attributed to DNA. Further, ribose is much more readily synthesized than deoxyribose under stimulated prebiotic conditions. A selective advantagesous RNA molecule would be one that directs the synthesis of protein that accelerates the replication of particular RNA (i.e, RNA polymerase). 

RNAs could have catalysed the formation of lipid like molecules that could have, in turn, formed plasma membrane and proteins. The proteins might have taken over most functions because they are catalysts than RNAs. If the first cells used RNA as their hereditary molecule then DNA evolved from an RNA template. Once cells evolved, DNA probably replaced RNA in most organisms.