In an experiment designed to show how life may have begun on Earth, scientists demonstrated that an electrical spark -- or lightning -- could produce amino acids, the building blocks of Earth' s life. However, unless the spark occurs in a "reducing" atmosphere, that is, one rich in hydrogen and lean in oxygen, amino acids do not form readily and tend to break apart when they do form. Scientists now believe that Earth' s atmosphere was actually rich in oxygen and lean in nitrogen at the time life began. Assuming that the scientists' current belief about Earth's atmosphere at the time life began is correct, which one of the following, if true, would most help to explain how lightning could have produced the first amino acids on Earth? ['Meteorite impacts at the time life began on Earth temporarily created a reducing atmosphere around the impact site.', 'A single amino acid could have been sufficient to begin the formation of life on Earth.', 'Lightning was less common on Earth at the time life began than it is now.', "Earth's atmosphere has changed significantly since fife first began."]