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.