We've put old rocks under the electronic microscope. That's how we identified billion year old cyanobacteria fossils. While there is no readily available comprehensive record of who searched for microfossils by looking at what old rocks, with or without a microscope, it's not like it's a new idea.
I feel like we're talking past each other here. The very first sentence of your link says "The cyanobacteria have an extensive fossil record." In the next paragraph it says "Cyanobacteria are among the easiest microfossils to recognize. Morphologies in the group have remained much the same for billions of years..."
So not a truly short-lived event in ancient sediments then.
https://ucmp.berkeley.edu/bacteria/cyanofr.html