There are countless animal and plant fossils from as far back as 100s of millions of years ago. Wouldn't we have found at least a few fossils of constructed objects?
Not much, since the ocean floor tends to be quite young on geological terms. For example, the oldest parts of the floor of the northern Atlantic ocean only started to form after Laurasia broke apart 50 million years ago, and the floor of the Pacific ocean is regularly recycled in the subduction zones of the pacific ring of fire.
Right, but organisms are small, get eaten, rot etc. Civilizations change their environment, build cities, manufacture tools with stronger materials. Advanced civilizations even more so.
still today, most of our civilization lives on the coast. The coast lines and ocean levels have changed significantly over the last 100million years. whole regions, such as where England used to be connected to mainland Europe, were just submerged.
Likewise Sundaland, whose mountaintops are now Indonesia; and Sahul, between Australia and New Guinea. Australians have oral records of the upheaval that came from that flooding.
