The “Big bang theory” describes the origins of the universe. Before there could be life on Earth, there needed to be a planet and universe to contain that life. Edwin Hubble discovered that the universe is expanding. From this rate of expansion, scientists were able to determine that the universe started from a single point of compressed gasses 15 billion years ago. The explosion of that point of compressed gas outward is the “Big bang theory”. From that explosion stars were formed and over time space debris and eventually planets (we are talking 15 billion years here).
The “Primordial soup” is the mixture of elements and gases which are thought to have started life on Earth.
Where did the gases and elements come from?