Final answer:
RNA, specifically ribosomal RNA (rRNA), was the basis for establishing the three-domain classification system. This system redefined the organization of life into Archaea, Bacteria, and Eukarya, thanks to the unique properties and ancient origins of RNA.
Step-by-step explanation:
The molecule that was the basis for establishing the three-domain classification system is RNA. The three-domain system, which includes Archaea, Bacteria, and Eukarya, was developed from comparisons of ribosomal RNA (rRNA) sequences. This molecular approach to phylogenetics has provided deeper insight into the evolutionary relationships between all forms of life on Earth.
The analysis of the rRNA led to the discovery that the microorganisms traditionally classified as bacteria are in fact divided into two groups with distinct molecular characteristics, causing a redefinition of the classification of life into the three domains. The RNA world hypothesis supports the notion that RNA could have been the first organic molecule to evolve, capable of carrying genetic information and executing cellular functions, predating DNA and proteins.
RNA not only stores genetic information like DNA but can also have catalytic functions like proteins. Hence, due to its unique properties and ancient origin, RNA was utilized as a molecular chronometer to establish a new taxonomy that reflects the evolutionary history of life.