What happened to, or where are, those who came before us?

I was flying commercial, several thousand feet above the Republic of Texas, looking down at the trees, the rivers, the tributaries, the land. Not that it matters but I was on my third bloody mary... potent little suckers. I had almost finished reading "1491," a captivating book that considers the Americas pre-Columbus, and supposes that the societys and cultures here were as vast and sophisticated, as complex and diverse as any in Europe at the time. And so looking down I was imagining the people of that time, managing their lives, farmers, hunters, craftspeople, warriors, politicians, artists perhaps. And I was thinking of the land itself, how if I was on the ground below I could just reach down and pick up a fossil, millions of years old perhaps. This area of Central Texas had once been underwater, a shallow sea and the build-up of shells as fossils, limestone as cliffs is enornmous. Maybe the water went all the way up and formed a shore along the the Llano Estacado, the high, staked plains above and to the west of Abilene. The oldest known human remains of North America have been discovered on those plains. Perhaps they were hunters following ancient herds of bison or mammoth. And then there is the Marty Robbins song, a sad but melodic refrain of lost love, somewhere out over the Llano Estacado. These thoughts, images and sounds were running through my head as the airplane dipped south and east, eventually flying along the Gulf of Mexico, over the great Mississippi just above New Orleans, bound for Atlanta and the busiest airspace and landing strips the world has ever known.