The burning of fossil fuels by humans is the largest source of emissions of carbon dioxide, which is one of the greenhouse gases that allows radiative forcing and contributes to global warming.
The genetic code. Efforts to understand how proteins are encoded began after DNA's structure was discovered in 1953. George Gamow postulated that sets of three bases must be employed to encode the 20 standard amino acids used by living cells to build proteins, which would allow a maximum of 43 = 64 amino acids.
The first question was how many DNA letters coded for each amino acid? If it was one DNA letter for one amino acid then you could only code for a maximum of four amino acids. Two letters in every possible combination could code for up to sixteen amino acids. Still, not enough. But three DNA letters provide more than enough combinations to code for all twenty amino acids.