i save the ends with the leaves as a treat for my guinea pigs. they sure like them a lot more than i do

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.

there are two “groups” of years. CE (common era) and BCE (before common era, also known as BC for “before christ”). we are currently in CE. There is no year zero, so 2023 years ago would be 1 BCE, and 2024 years ago would be 2 BCE. BCE years count up as you move into the past, and CE years count up as you move into the future. when you see something referred to as happening in, say, 500 BCE, that is 500 years before the common era, or 2523 years in the past.