Your explanation of a need to find evidence of these past cultures is outwardly both logical and easily acceptable, but how many fantastic finds of historical importance have we only just recently discovered via our advances in technology. I believe we are still only just beginning to discover the secrets of our long lost past civilizations. That whole army of clay soldiers found by accident by a farmer plowing a field in China, or what about the discovery one of the earliest known settlements of native cultures in the Pacific Northwest just recently uncovered while they were doing construction on one of the ferry docks here in Washington State, both are ancient sites. Both have proven to be among the most significant finds of our times.
Another find, proven to be as valuable, in the Middle East, is a town that was located along an ancient trade route and found to contain some of the most complete and unique examples of Roman mosaic art and design ever known to exist. This site also contained other eye opening examples of sophisticated architecture never before seen. Unfortunate that a public works project halted this dramatic discovery and flooded the entire valley where it was located. Even though the brief excavation of this site had produced historic examples of decorative art, the likes of which had never been seen before, the entire site is now submerged under a vast lake of water. The government would not allow further exploration to disrupt their scheduled flooding of the area. All of what was within our reach is no more. We may never know what else now lies below the lake in this ancient city until such time as advances in underwater exploration can reveal such. It makes me wonder how much of our collective past will be lost due to that huge dam that is now being built in China.
Who can say how long it may take to develop sufficient methods and technologies to adequately explore our earth. We are only just beginning to discover ways and means to explore what lies below the very ground on which we walk. There are other fantastic archeological finds to be uncovered and understood. We won't find them all in our lifetime.