Final answer:
The Big Bang occurred approximately 13.7 billion years ago and marked the beginning of the universe. It was a rapid expansion of space itself rather than an explosion of particles. This event is supported by evidence such as the isotropic and expanding nature of the universe and the presence of cosmic background radiation.
Step-by-step explanation:
The Big Bang occurred approximately 13.7 billion years ago according to current scientific estimates. The Big Bang was not an explosion of particles through space, but a rapid expansion of space itself. This event marked the beginning of the universe as we know it and is supported by evidence such as the isotropic and expanding nature of the universe and the presence of cosmic background radiation.