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It is a mystery how the earliest organisms on earth evolved the means to thrive, grow and reproduce under the sparse conditions of the young planet. Primordial earth had little oxygen and in the deep seas, no available light. One theory proposes that life evolved near undersea vents, taking energy from gasses bubbling up from earth's interior. There is a known metabolic pathway – called the Wood-Ljungdahl pathway – that works in an oxygen-poor environment to transform hydrogen gas and carbon dioxide to usable energy and cellular building blocks. Genetic evidence suggests that this pathway originated in Earth’s earliest eras. Today, billions of years later, this pathway is still used by bacteria and archaea across environments and ecosystems, including in our own digestive tracts. Its biochemistry is complex and bizarre, but over the past hundred years, its mechanisms have been clarified piece by piece, each step making use of new technologies. Today, we are learning more about the Wood-Ljungdahl reactions using X-rays from synchrotrons such as those generated by the Stanford Synchrotron Radiation Lightsource at SLAC. This lecture will describe the development of our knowledge of this ancient pathway and the way that modern tools illuminate this chemical messenger from the dawn of life.