It has been noted by people who calculate such things that if the 4.5 billion years this planet has been a-making were converted to a 24-hour clock, we humans have been here less than five minutes. Sixty-six million years ago, give or take a few months, what must have looked to the universe to be a small pebble hurtled through the blackness we humans would eventually call “space” and crashed into a larger rock circling what humans eventually would call The Sun.
Somewhere near the head of a stream, water seeps slowly into a flaw in the granite. Winter cold freezes the mixture of oxygen and hydrogen into an expanding wedge that forces the boulder to crack in two pieces, then more. Gradually, over several winters, the stream grows larger and the boulder pieces smaller.