Primordial soup is the theory that life began in a warm (or hot) pond or ocean of water. The ingredients aren't known and only supposed from studies of ancient rocks, dating of different materials, and from supposed knowledge of how the earth was when life began. The recipe becomes even more difficult to calculate when we can not observe the formation of life, either on earth today or in the lab through experiments.
Primordial soup requires the perfect combination of ingredients to form amino acids, which would then combine into proteins, and finally into nucleic acids. These nucleic acids would then need to work together to form simple single celled organisms and the beginning of life on earth.
For primordial soup to create life on earth it is believed that some of the components of the "recipe" would have to be nitrogen and carbon dioxide. These gases were known to be on the earth during the formation of life. Additionally iron and carbonate minerals would have been on the earth and are a necessary part of the soup. This is because energy (such as lightning) passed through the gases would produce amino acids as long as there was iron and carbonates to neutralize the acidity of the mixture.
The next big ingredient believed to be a part of the recipe for life would have to be pantetheine. This is a chemical that closely resembles enzyme A. Enzyme A is used by living things to turn amino acids into protiens. Scientists now believe that pantetheine may have been used in early times to combine amino acids into proteins. Further studies have shown that pantetheine can be made from pantoyl lactone, beta- alanine, and cysteamine (three chemicals thought to have been on the earth during the period life began) at 105 degrees F.
Additional ingredients would be necessary in order to have proteins combine and form nucleic acids. What these ingredients are, we can't be sure and aren't even positive as to where to turn to now. It is possible the meteorites and other materials from the stars had an impact on the development of life on earth. They could have added additional chemicals and or materials as well as changed heat and pressure of the ingredients in the soup to have an unknown effect.
All we can be certain of is that if life began in a primordial soup then things that we have not yet observed (either in nature or in the laboratory) would have to have happened. Research continues to work on reproducing early earth conditions and providing evidence of life spurring from a soup of ingredients.