It is not easy to get an idea of what a billion years means. Obviously, it is a long period of time, but it is tough to imagine.
One way to try to get a grasp on long periods of time is to compare them to more familiar periods of time. Let’s look at spans of time leading back to four billion years ago.
The United States of America didn’t exist four hundred (400) years ago.
The great pyramids of Egypt were built a little over four thousand (4,000) years ago.
Humans did not inhabit the Americas until forty thousand (40,000) years ago.
Humans had not finished evolving from apes four hundred thousand (400,000) years ago.
Apes began to evolve into human species some four million (4,000,000) years ago.
The Rocky Mountains in the United States were created at least forty million (40,000,000) years ago.
The first invertebrates (creatures without spines) crawled from the water onto land some four hundred million (400,000,000) years ago.
More than four billion (4,000,000,000) years ago, a chunk of space debris became Earth.
Such lengths of time still aren’t easy to imagine!