Final answer:
In 1981, Thomas Cech and colleagues discovered RNA as a self-replicating molecule, contributing to the concept of the RNA world hypothesis, where RNA possibly preceded DNA and proteins in early life forms.
Step-by-step explanation:
The self-replicating molecule discovered by Thomas Cech and colleagues in 1981 is RNA. This discovery contributed to the development of the RNA world hypothesis, which speculates that RNA could store genetic information and catalyze chemical reactions, possibly preceding DNA and proteins in the evolution of life. The concept of an RNA world addresses the "chicken-and-egg" problem by presenting a scenario where a single type of molecule could both carry genetic information and perform cellular functions. The structure and replication of RNA, along with its ability to catalyze its own synthesis under certain conditions, provides a compelling argument for RNA's potential role in the early stages of life on Earth.