How did "they" (aka humans), found iron melting possible, and where first? And why it spread so fast in comparisson with other human discoveries. And why all really advance bronze age civilizations where completely anihilated by iron age "tribes"invasion. Besides the obvious reason of those tribes having iron weapons.
Small-scale iron smelting was present in the in the Bronze Age in Egypt, Mesopotamia, Anatolia, Cyprus, and India, with objects being produced from c.1800 BC onwards.^1 Production on a large scale began after 1200 BC, and gradually increased in use over the next 400-500 years, until it was a common everyday metal.^2
It isn't really true that the Bronze Age civilisations were destroyed by tribes wielding iron weapons. The destructions at Aegean and Near Eastern sites occur in the decades around 1200 BC, when almost all weapons were made of bronze. It is also the case that early iron objects were not superior to bronze,^3 and it is the carburised steel which is produced slightly later^4 that gives iron objects physical superiority to bronze
^1 Waldbaum (1980) From Bronze to Iron: The Transition from the Bronze Age to the Iron Age in the Eastern Mediterranean; Rakesh (2003) "The Origins of Iron Working in India: New evidence from the Central Ganga plain and the Eastern Vindhyas" Antiquity 77.
^2 Snodgrass (1980) "Iron and Early Metallurgy in the Mediterranean", in The Coming of the Age of Iron.
^3 Muhly et al. (1985) "Iron in Anatolia and the Nature of the Hittite Iron Industry" Anatolian Studies 35.
^4 Yalçın (1999) "Early Iron Metallurgy in Anatolia" Anatolian Studies 49.