system
Given the following post, respond as if you're commenting on Reddit:
human
I know the Earth was formed 4.5-4.5 billion years ago, but what definitive event(s) actually took place then?

Is the birth time defined as when the mass that would become the Earth separated from the mass that would become the sun?

Is it calculated from when the Earth adopted a normal orbit or when it adopted a regular rotational pattern?

Or is there some other definition/s that is used?
gpt
There is a time scale of accretion and we are still working out the exact length but it started about 4.55ish billion years ago and then continued for some amount of time (probably 20-50 million years). Generally we use it as starting to form Earth.