THIS PROPOSAL DESCRIBES WORK THAT IS PART OF A LARGER NASA-SPONSORED EFFORT TO UNDERSTAND THE ORIGIN OF LIFE ON EARTH, WHICH WILL GUIDE THE SEARCH FOR LIFE ELSEWHERE IN THE UNIVERSE. IT PERTAINS TO A FORM OF RNA-BASED LIFE THAT LIKELY EXISTED DURING EARTH S EARLY HISTORY, AS A PREDECESSOR TO THE CURRENT DNA-RNA-PROTEIN-BASED LIFE. THE PROPOSED RESEARCH AIMS TO CONSTRUCT RNA-BASED LIFE IN THE LABORATORY AS REPRESENTED BY POPULATIONS OF RNA ENZYMES THAT CATALYZE THEIR OWN REPLICATION AND UNDERGO DARWINIAN EVOLUTION IN A SELF-SUSTAINED MANNER. THE RESEARCH ALSO SEEKS TO UNDERSTAND MOLECULAR PROCESSES THAT ARE FUNDAMENTAL TO THE ORIGIN OF LIFE ON EARTH AND ELSEWHERE. DURING THE COURSE OF PRIOR NASA-SPONSORED RESEARCH, OUR LABORATORY DEVELOPED THE FIRST EXAMPLE OF AN RNA ENZYME THAT CATALYZES ITS OWN REPLICATION AND CAN TRANSMIT HERITABLE INFORMATION FROM PARENT TO PROGENY MOLECULES. THIS SYSTEM INVOLVES PAIRS OF RNA ENZYMES THAT CATALYZE EACH OTHER S SYNTHESIS BY JOINING TOGETHER COMPONENT OLIGONUCLEOTIDE BUILDING BLOCKS. EACH BUILDING BLOCK CAN HAVE MANY ALTERNATIVE COMPOSITIONS AND CAN BE JOINED IN MANY DIFFERENT COMBINATIONS. IN ADDITION, NEW VARIANTS CAN ARISE THROUGH RECOMBINATION DURING THE COURSE OF REPLICATION. VARIANTS THAT REPLICATE MOST EFFICIENTLY GROW TO DOMINATE THE POPULATION UNTIL NEW, MORE ADVANTAGEOUS VARIANTS ARISE, RESULTING IN AN ONGOING DARWINIAN BATTLE FOR SURVIVAL. THE PROPOSED RESEARCH AIMS TO INCREASE THE COMPLEXITY OF THE PRESENT RNA-BASED EVOLVING SYSTEM SO THAT IT CAN BRING ABOUT THE INVENTION OF NOVEL FUNCTION. LARGE, HETEROGENEOUS POPULATIONS OF SELF-REPLICATING RNAS WILL BE CHALLENGED TO ADAPT TO VARIOUS ENVIRONMENTAL CONDITIONS, RESULTING IN THE EMERGENCE OF NOVEL FUNCTIONAL TRAITS THAT CONFER SELECTIVE ADVANTAGE. AS THE ENVIRONMENTAL CONDITIONS CHANGE, FURTHER ADAPTATIONS WILL ARISE THROUGH EVOLUTIONARY PROCESSES THAT CAN BE CONTINUED INDEFINITELY. THIS WORK HAS THE POTENTIAL TO PROVIDE THE FIRST EXAMPLE OF A LIVING SYSTEM OUTSIDE OF TERRESTRIAL BIOLOGY. IT ALSO WILL SHED LIGHT ON THE CHEMICAL BASIS OF LIFE AND ON THE PRESUMED ANCESTOR OF CONTEMPORARY LIFE ON EARTH.