Why Is There No Record Of Ancient Humans?

As I understand it the earliest modern human skeletal remains (biologically identical and presumably with comparable intelligence levels of humans today) have been dated to 150 - 160 thousand years BP (Before Present). At the same time the earliest record of human history reaches back only as far as roughly 6000 BP. So... if it so happened that there were modern humans living for all this time... why is there no history? What happened in the past 150,000 years?

An answer may perhaps be found in geological records of cataclysmic events during past 150,000 years. Randall Carlson did some amazing work gathering this information. He gave a very interesting talk on the subject.

Above is a diagram of events that happened in the past 150,000 years that can be categorized as catastrophic. In other words, events of a magnitude that would have the potential to reset our modern, technologically advanced society to the stone ages were they to happen today. 

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At the same time there are ancient megalithic structures found all over the planet that stem from a time long before different human cultures allegedly began sailing the oceans and started interacting with each other.

Yet they share many similarities. Very ancient and weathered, but sophisticated poligonal walls built from very large and hard stone blocks that often weigh many tons each can be found in different locations across the globe. Here are some examples collected from Jimmy's great video:

They also share curious nobs on some of their surfaces that no one has a good explanation for.

There are also Pyramids across the globe, not only in Egypt... and even the Egyptian pyramids seem to predate the ancient Egyptian cultures. So who built all these structures? Could it have been a civilization that we have no record of? How far back does the human story actually go? How far have we come before? These question have been nagging on my mind for years. As Graham Hancock says: "We are a species with amnesia." Man, I would LOVE to know the truth and explore this further!