I'm not sure, There are things alluded to like airplanes, submarines, possibly nuclear weapons, extra-terrestrial visitations. Who built the Sphinx, the pyramids, the giant stone monoliths, some of the ancient cities, accurate maps of Antarctica showing it without the ice. After thousands of years how much of our civilization would be easy to discover. The similarities around the world of certain empires when communication of that type was considered virtually impossible. I would like to see how these can be explained. I am curious and a casual observer, but some things just do not appear to add up. So any knowledge you can impart would be appreciated.

The ancient Egyptians built the Sphinx and the pyramids, and the means they used to do so are well documented. You're surrendering to pseudoscience.

That would depend a lot on the time frame. Most of the evidence of our civilization would likely disappear in in ten thousand years or so. We are still discovering new things every year. Stone cities and underground cities for instance. They are still discovering new things about the pyramids, the sphinx and discovering more ancient burial sites. Nazca seems to be a very strange site with the top of mountains leveled off and the lines. Perhaps the translations of some of the texts are in error.

I'm not sure I think they were Sumerian tablets, I believe there are also surviving texts in India that have only been partially deciphered.

@orion
You cite ancient texts but you don't know what they are?