Thanks goodness for metal that recyclable and sustainable substance. Recently this was highlighted by the case of a recently discovered sky disc, found by treasure hunters in Saxony. The sky disc shows a sophistication previously not attributed to the Bronze Age and demonstrates a strong knowledge of the celestial that surprised experts. Crafted from copper and tin the object of art, wonder and knowledge was able to survive the ravages of time, buried in a Saxon forest, for over 1500 years. Thanks goodness it wasn't carved out of wood. What metal objects will you pass along? The durability and amenability to recycle metals was something known to the ancients and makes metals, and by inference mining, the most sustainable of substances and activities respectively.