Our minds are simply incapable of understanding ideas like million or billion. My son said, "I'm gonna count to a million. One, two, a million". Counting at one per second, eight hours per day, it would take over a month to count that much. Counting to a billion would take a lifetime.
It's almost like our minds shut down. You see "millions and millions", or "billions and billions" and you say, "well, I guess anything could happen". It is completely outside of our experience, our framework for living.
When you allow for billions of years in history, huge gaps seem like minor cracks.
There is no recorded history more than 6,000 years old. There are some claims the Babylonians started slightly earlier, but then there are big gaps where, seemingly, nothing happened.
One billion years is 166,000 times longer than that. That's like 30 times all of recorded history every year for all of recorded history.
Science News tells us that there was a gap of one billion years in history where nothing happened.
That's twice as long as the time it is supposed to have taken simple one celled organisms to turn into people who can travel in space.
Everett Dirksen is attributed with the quote, "A billion here, a billion there, pretty soon, you're talking real money". I see some parallelism...