Montmorillonite, a clay mineral formed by the weathering of volcanic ash, may have played a central role in the evolution of life. Because of its structure, montmorillonite tends to adsorb organic compounds and this contributes to its ability to catalyze a variety of organic reactions critical to scenarios of life's origins. We have shown experimentally that RNA molecules bind efficiently to clays and that montmorillonite can catalyze the formation of longer molecules (oligomers), thus lending support to the RNA world hypothesis. This theory proposes that life based on RNA preceded current life, which is based on DNA and protein.