Was iron important for the first life on Earth?
Cyanobacteria require iron for photosynthesis and can be found as fossil stromatolites dating back to 3.5 billion years ago.  Stromatolites are layered structures made up of cyanobacteria and sediment.  



Source: https://en.wikipedia.org/wiki/Stromatolite

Modern stromatolites can be found at Shark Bay in Australia, Chetumal Bay in Belize, and Laguna Bacalar in the Yucatan Peninsula.  

Cyanobacteria are also believed to have evolved into the first microbes to produce oxygen by photosynthesis, which was a catalyst for the Great Oxygenation Event which occurred around 2.45 billion years ago.