Great Annihilation

The Great Annihilation was an event that occurred 13.7 billion years ago, and is generally considered to be the final event of Genesis.

During this event, huge amounts of n-matter and antimatter were created from pure energy. This matter and antimatter filled almost the entire volume of the early Universe. Almost immediately after their creation, the matter and antimatter particles underwent annihilation. This reverted all of the antimatter and nearly all of the n-matter to energy, creating what would become the cosmic microwave background.

The surviving matter went on to build the rest of the physical Universe.