Earth-616 is one of the many infinite worlds in The Multiverse, and a catalyst in the events leading up to the War Against the Villain Armada. It has a population of 7 billion people before the Great Invasion of Earth-616, and the War Against the Villain Armada, an event in which 1 billion people were killed, and only 6 billion people remained in Earth-616.
The Nexus Explosion Edit
Earth-616, just like all other Infinite Earths within the Multiverse, was nothing but a singularity. Before the Multiverse was created, there were 6 Singularities, which were massive Conduits of power for an ancient race of Superhumans known as 'The Celestials'.
However, just as The Celestials gained control of these Conduits, the Multiverse exploded into existence after a SuperNova known as The Big Bang, which caused a huge repulse post-triggering and turned the one intended Earth into Infinite Earths, which is an infinite amount of Human-populated planets within The Multiverse. There are other theories of the Multiverse within Religion, an example would be God's 6 Days of Creation.