Step-by-step explanation:
Big Bang theory is the most widely accepted model of the Universe formation. The most powerful evidence in support of this model was the discovery of Cosmic Microwave Background(CMB) radiation in 1964. When astronomers tried to find out the source of this radiation they couldn't associate with any star, nebula, galaxy or any other object.
This radiation can be traced back to the Recombination epoch when first neutral hydrogen atoms started forming and the space started getting dark and transparent.
In the year 1990, Cosmic Background Explorer Satellite (COBE) showed the frequency spectrum of CMB radiation. Thus, further supporting the discovery of CMB radiation and its connection with Big Bang.