What led to the three domain classification system?

The three-domain classification system emerged from advancements in molecular biology, particularly the sequencing of ribosomal RNA (rRNA). Carl Woese’s research in the 1970s and 1980s revealed that rRNA sequences could provide insights into the evolutionary relationships among organisms. His work demonstrated that the genetic differences between Archaea and Bacteria were as significant as those between Bacteria and Eukarya, leading to the adoption of the three-domain system in 1990.