For many years, the evolution of protein production (called translation) seemed like a bit of a chicken-and-egg problem. The complex that catalyzes translation, the ribosome, contains both RNA and proteins, which causes a bit of a paradox: how did the first proteins get made if their production required the ribosome's proteins? Decades ago, Francis Crick had suggested a simple solution, where the chemical reactions that link a chain of amino acids into a protein were catalyzed by RNA. But, for many years, this suggestion was largely ignored, as many assumed that the ribosomal RNA did little more than act as scaffolding for the complex's proteins.
But, over time, bits of biochemical evidence suggested Crick might have been on to something, as they hinted that the ribosomal RNA might be a bit more than inert scaffolding. Ultimately, the conclusive evidence came when researchers finally determined the structure of an intact ribosome, and located the active site. There were no proteins at the site, simply RNA.