Why present perfect?
Copper and tin were used before iron: they melt at a lowe temperature, and can be mixed to form a useful metal called bronze. Iron was probably extracted from meteorites, perhaps around 3000 BC. (Iron ornaments dating from 5,000 years ago HAVE BEEN FOUND in the Middle East.) Later, iron was extracted from iron ore, around 2000 BC...
Why have been found? Were found ---- wrong?