The Discovery of Penicillin
Alexander Fleming returned from holiday to find mold had contaminated a petri dish and killed the bacteria around it. He published, and little happened for a decade until a team at Oxford worked out how to purify and mass-produce it, in time for the Second World War. Before antibiotics, a scratch could kill; afterward, infections that had killed for all of human history became a prescription. Together with sanitation and vaccination, it helped add decades to average life spans within a single generation.
A new way to record or transmit information lowers the cost of copying ideas and reorders who holds knowledge and power.