A closer sight showed that these pieces had been left behind in the fires of ancient peoples who had melted rocks to get metals,looking around, he found more and more information,until the history of what men had done at the place over tens of centuries was known.

【翻译】进一步仔细的观察表明，这些碎片被遗留在古人的火堆中，他们为了获取金属而熔化了岩石。他环顾四周，发现了越来越多的信息，直到千百年来人类在此地方生活的历史为人所知。

最后从句的主干是：until the history was known. 直到这段历史为后人所知。