When we are talking about years that long ago, we typically just say mya (million years ago or Ma for mega annum), or Ga for giga annum (billion years), at least this is true in my line of study, which is geology. As @fondots explained above, 1CE is considered the birth yeah of Jesus, hence years before the common era being called BC, for before Christ, before BCE became more common. Since humans (at least as Homo sapiens) weren’t around 5 million years ago, as geologists, we don’t really consider those years to be part of the BCE year group.
When we are talking about years that long ago, we typically just say mya (million years ago or Ma for mega annum), or Ga for giga annum (billion years), at least this is true in my line of study, which is geology. As @fondots explained above, 1CE is considered the birth yeah of Jesus, hence years before the common era being called BC, for before Christ, before BCE became more common. Since humans (at least as Homo sapiens) weren’t around 5 million years ago, as geologists, we don’t really consider those years to be part of the BCE year group.