On: Could an industrial civilization have predated humans on Earth?

[hutzlibu]

Then they made some leaps.

Casting iron(copper) is relativly easy and powerful.

Experiment with hot things in fire and you will discover it after a while.

"Why couldn’t they have use some natural form of biodegradable materials?"

Like bones for bows and spears? Humans did that, but metal is apparently more effective and useful.