Brian Foerster in this video tells a theory that Incas built their city on top of an older one, judging by the difference in the block material (granite), size, and the precision of their composition. Couldn't we verify this using scientific methods of age detection?
Although opinions differ, the overwhelming academic view as things stand is that construction at Machu Picchu began around 1450. I don't think anyone is completely ruling out an earlier temple being built on the site before that, but the 'evidence' in the video is pretty scanty: it's well-established that precision stone-working had been in place in the Andes for hundreds of years before the Incas, for example at Tiwanaku in Bolivia (some pictures) or at sites like Sillustani near Lake Titicaca.
As for the different stone being used, the granite used as shown in the video was also used at demonstrably Inca sites such as Ollantaytambo, so again it's hard to see this as 'proof' of MP being built by a different civilization. Sorry, but there we are...
Not to mention many natives that knew of the area claimed it wasn't the Incas that built Machu Picchu, but hey what do savages know? The best way to look at what happened in the past, is to look at what is happening today, still doesn't paint the full picture, though it helps. How many low tech groups of people are making beautiful stone structures on mountain tops in this day? Well none we know of. So that implies someone of fairly evolved technology had gone up there and settled the plateau. Those people could have very well died off, then other people moved in. If I discovered Machu Picchu, I'd move in too, just look at that view.