Human impact on the Earth

It is said that were mankind to be wiped out, traces showing we had existed would very quickly disappear. Over hundreds of millions of years this is largely true. But just as we can in a few places still find rocks formed billions of years ago, for many millions of years our impact on the earth would remain visible. Just as some things humans did thousands of years ago remain today.

The puzzle is that some ancient constructions are close to impossible even with modern technology. They appear to be completely impossible with the technology known to exist at the time. There are not many of these. Ancient humans were very competent in working and using stone. But even one apparently impossible achievement of ancient humans should be enough to demand we investigate more deeply.

The achievements in this category are:
- The really large stones at Baalbeck.
- The similarly large stones that were being cut in China.
- The precision of stone cutting in Peru.
- The precision of stone cutting and building in Egypt.
- The probable existence of megalithic constructions under the sea, that must have been built before 20K BCE.

The related puzzle is that if these achievements were the result of high technology now lost, we have no evidence of how an ancient civilisation could have developed such technology, without leaving visible marks on the earth. Development of our high technology has required mining and industrial sites that have cut into and re-shaped significant areas of land.