Most scientists agree that we, as humans, have been basically the same for about 50,000 years. We have had the same sized brains, thought potential, reasoning skills. however, however, civilization has only been around for 5,000 years. That means that we have been hunter gatherer cave men for 90% of the time we have been on earth, and have made all of this in the last 10%.
It hasn’t exactly been a straight through March of technology either. when the Western Roman Empire ceased to exist in September of 476 we had air conditioned and heated villas, running water, and power tools. We didn’t get bathrooms with running water again for 1,400 years. An old friend of mine used to joke “Christopher Columbus should have landed on Mars”.
Realistically, civilization can advance to this level in less then 4,000 years. Chronologically, that means we could have advanced to this level 6 times before our current civilization. I think it would be realistic to say we advanced a few times. Some that didn’t make it to this level, and some that possibly made it past our current level.
Why then, is there no evidence of these previous civilizations?
Scientists admit that almost all of our technology, if left un-maintained, would only take 10,000 years to oxidize, decompose, or rot back into its raw forms. Cars and steel skyscrapers will rust and become iron oxide eventually become iron deposits once again. The only thing that will be left will be things carved in stone. Things like the Pyramids, Stone Henge, or Mt Rushmore.
It would take far less time for our items to disappear from the face of the earth if subject to the corrosive elements of the sea. Considering the changes in sea levels over the last 50,000 years, and our dependence on the sea, it is safe to assume that any advanced civilization would be coastal. Therefore any advanced civilization that may have existed in the distant past would have disappeared without a trace.
What could have happened to them?
There are many things that can decimate a civilization, and knock them back to the stone age. War brought down the Western Roman Empire, and pestilence kept it down. Within decades of the fall of Rome people were building cities next to old Roman cities because they no longer had the ability to maintain the infrastructure. Climate change could destroy a civilization just as easy. The onset of an ice age would destroy once fertile lands and drop temperatures to make whole areas uninhabitable. The end of an ice age would bring dramatic rises in sea levels flooding island or coastal civilizations. Super Volcano eruptions could blanket continents in burning ash, and block out the sun for years. Volcanic winters would create ice age type conditions that would also spell the end for civilizations. And let’s not forget impacts. An asteroid impact could create an extinction level event like the one that took out the dinosaurs, but a smaller sized impact could wipe out civilizations, make farm lands infertile, wipe out live stock, and create acid rain.
Is it not in the realm of possibilities that an ancient, advanced civilization would be able to predict a coming catastrophe, and leave this planet in an attempt to escape an apocalyptic event? Those left behind would be forced to face the destruction, and the survivors would have to rebuild from scratch.
Picture the scenario: the political, financial and social elite of an highly advanced, ancient human civilization flee into space to escape a worldwide global warming (end of an ice age). The poor and under educated that are left behind blindly meet the rising seas that wipe out their cities. The scattered few that make it inland have to scavenge to survive. With books and electronics destroyed by the waters, they have no way to rebuild the civilization they once new. As the generations pass the old world fades into myth.
The ones who escaped travel through space for years, decades, maybe centuries before finding a new world to inhabit.Eventual, maybe generations later, they find another planet that can sustain life. They have brought with them the tomes of knowledge from their civilization. and they continue to advance. They could be 10,000, 20,000, 30,000 years more advanced then we are today. Could they not be the ones that come back here to see what became of the ones they left behind? To visit their ancestral home world? Maybe the UFO’s we see in the skies above us are not alien lifeforms from some far off galaxy, but instead a divergent lineage of us…