Agreed. Why couldn't we simply have had a pre-existing Earth civilization that arose, developed technology/industry, and faded away, leaving only resilient megalithic traces?
There is ZERO evidence for such a civilization. Especially because there are no resilient megalithic traces in the first place. Megaliths we see are only 5-6 thousand years old and have a lot of matching real evidence about people who built them and how they did it.
- Didn't affect the atmosphere in any way.
- Had all their buildings were recorded as being built by a people we know much about in specific timelines we know much about, which aligns with archeological artifacts.
- Made sure none of their lithics stayed.
- Used no fuel source.
- Did no mining of any kind.
- Never used anything but stone and paper machete for building (because even wood structures leave identifiable patterns for potentially thousands of years).
- Only used that stone for a couple buildings, which they planned for the cultures that didn't exist to use intimately.
- Had their bones dissolved without a trace.
All we have to do is remove any type of evidence-based science and anything is possible!