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 code is actually the sequence of bases in DNA. For example ATAGCGA... is a code for part of a protein. The entire protein would actually require a much longer sequence of DNA bases. Whenever a protein needs to be made, the correct DNA sequence for that protein is copied to a molecule called messenger RNA (mRNA).