There is no end to the important historical moments in the history of human use of copper. Discovered in 8000 BC, copper was used as an early tool by humans because it could be worked with in its native state. Over the next several thousand years, copper would be the metal to set a number of firsts. In 5000 BC, it became the first metal that humans smelted from sulfide ores. In 4000 BC, it was the first metal cast into specific shapes. In 3500 BC, it was the first metal that humans purposely alloyed with another metal, tin, to create a third metal, bronze. This latter achievement brought about the Bronze Age of human civilization. The obverse and reverse designs of the 100 oz Copper Bars in this listing come with varying designs. The images on these bars are often limited to the obverse field, with inscriptions stamped into the bar that identify the mint of origin or brand it was produced for, as well as the weight, metal content, and purity. On the reverse, you will typically find a blank field, though it may have natural textures that result from the production process.