Just a thought
Could some sort of extraterrestrial nanoplague have been responsible?
Evidence:
Exhibit A:- A widespread iridium layer present in the K-T boundary worldwide
Exhibit B:- Evidence of OOParts such as apparent screws embedded in >100MY old coal
Exhibit C:- Lots of apparently unrelated extinctions in both oceanic and terrestrial life
Exhibit D:- Weird spikes in certain rare metals not usually found in meteorites
I theorize that some sort of self replicating alien probe turned up and due to a massive miscalculation it entered the Earth's atmosphere and dumped its nanotechnological self repair mechanism when it burned up along with the controls and failsafes.
If iridium ions are essential then perhaps the replicators spread worldwide and ended up nearly destroying the biosphere before using all the native iridium up and running out of raw materials.
As it happens some of the material might have survived and be buried tens of miles underground or in deep caverns, yet to be discovered.
Biting the hand that feeds IT
