OOPARTS appear to come in two basic forms. Conventional (modern) things located in the "wrong" place, such as the gold chain located in a deep deposit of coal. How it got there is an 'unknown' however it got there, thus it can happen. There isn't much more to say to that. The second part of OOPARTS like the Baghdad Battery and the The Antikythera mechanism make this terrible assumption that we humans are dumber than we really are. The Science channels recently (over the past couple of years) have covered the question "What would happen if mankind vanished?" They address what would happen to all of our "stuff" you know cities, buildings, cars, dams, etc. What is simply amazing is that most of our "stuff" would be gone in 1000 years, collapsed and buried for the most part. In 5 thousand years things like concrete, steel, glass, brick would degrade and "return" to an earlier state - iron rust, clay dust, glass broken into sandy bits. In ten thousand years even our most enduring piles of "stuff" containing large amounts of plastics would be much harder to find - our landfills would be well on the way of decomposition with the organic materials transformed long ago into an organic soup, the metal buts converted to oxides and the plastic bits disintegrated and becoming "oil" again. We are, seemingly, a species that suffers from racial memory loss. We believe that the Sphinx was built was built in 2500 BC in the time of the pharaoh Chephren (of Khafre) - however the geologic data and weathering of the surrounding soils and rocks suggest that the sphinx must have been carved out of the living rock over 10,000 years ago. There appears to be myth and stories we have passed down through the generations from various cultures around the globe that hint at an earlier, greater era in human history when we had achieved technological prowess close to early industrialization (Late 19th Century early 20th century). We now know that Ancient Greeks and Ancient Romans had far greater understanding of technology. Automatic machinery was the "norm" in Greek Temple construction, pneumatics, hydrolics and water power was well known and used globally at a time prior to the great expanses and conquests of the Roman Empire. Historically we have clear evidence of one technologically superior culture collapsing ushering in an age of "lost" technology that we call the "Dark Ages". When Rome fell she took a lot of human progress with her. We are only now in the 20th and 21st centuries digging up the real extent of Roman and Greek ingenuity and with dawning realization we are seeing the Romans and Ancient Greeks in a new light, one of greater sophistication that in many ways rivals our own current technological prowess in many areas. I suspect we humans have had earlier great empires and a rise in technology that gave us things like the Baghdad Battery, The Antikythera mechanism and other tools and bits and pieces that we barely remembered after some "great cataclysm". History (that which we know) demonstrates that men are born and die and that empires rise, then fall. This is "normal" for our species and in earlier collapses of earlier civilizations we have "lost" a great deal of knowledge and understanding of our world entering into "dark ages" where we had to climb back out of these pits and rediscover things discovered earlier on. I suspect that the latter type of OOPARTS are bits and pieces of even earlier civilizations that we have forgotten we had, ones that rose up and due to various reasons collapsed with only a tiny fraction of the knowledge gained carried forth to the next civilization. In our society collapsed today, in 10,000 years very little would remain to show that we once had gleaming skyscrapers and the ability to fly. Any defendants would think of us as Gods if they even remembered us. Earliest modern man had the same physical abilities such as we have today. The ability to reason, to think, to explore and to question the world about him. I find it difficult to believe that for thousands of years prior to the known rise of civilization we lived in complete ignorance. Instead I think that we rose up a tad, were knocked back k down - again and again. There is genetic evidence for a bottle neck in our species - a period of time where humanity was reduced to a very small population - this was most likely due to the eruption of a super volcano. Then we have the Ice Age - we survived, but anything buried under the ice would have been ground up and buried very deep. The Earth is a dynamic planet that swiftly changes and easily grids down anything we humans can build. And we are a species that seems to have a small talent for war and the seed of self destruction in our hearts - so there are many ways that we could lose a lot of what we discovered, leaving rare bits and pieces to be dug up and speculated about.