Meteorites are sourced from the sky.

Meteorite iron has a specific percentage of nickel, and iron from the earth has almost none, among other distinctions (sometimes iridium).

https://en.wikipedia.org/wiki/Tutankhamun%27s_meteoric_iron_dagger

As far as the Earth being covered by them, if we didn't have a water cycle and weather, the surface of the Earth would look like the moon. Civilization has only been experimenting with melting nuggets such as copper and tin for a few thousand years.

I wish I had a good source for that but, I don't.

When copper became useful, surface copper was taken first before deep mining was used. Same with tin and iron. If Iron weapons were made before and iron mine was operated, they used surface iron.

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I'm an anonymous poster on the internet, and I'm actually full of a steaming pile of manure.