Learning objectives
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Original figure description: Diagram of the Miller-Urey experiment. A flask of water (to simulate the ocean) is heated. This is connected via glass tubing in a closed loop to: a vacuum pump, a flask containing gases (water, methane, hydrogen, ammonia), and an electric spark (to simulate lightning), and final to a condenser that cools the water. The cooled water contains organic compounds.
The earth is estimated to be 4.6 billion years old, but for the first 2 billion years, the atmosphere lacked oxygen, without which the earth could not support life as we know it. One hypothesis about how life emerged on earth involves the concept of a “primordial soup.” This idea proposes that life began in a body of water when metals and gases from the atmosphere combined with a source of energy, such as lightning or ultraviolet light, to form the carbon compounds that are the chemical building blocks of life. In 1952, Stanley Miller (1930–2007), a graduate student at the University of Chicago, and his professor Harold Urey (1893–1981), set out to confirm this hypothesis in a now-famous experiment. Miller and Urey combined what they believed to be the major components of the earth’s early atmosphere—water (H2O), methane (CH4), hydrogen (H2), and ammonia (NH3)—and sealed them in a sterile flask. Next, they heated the flask to produce water vapor and passed electric sparks through the mixture to mimic lightning in the atmosphere (OSC_Microbio_07_00_splash). When they analyzed the contents of the flask a week later, they found amino acids, the structural units of proteins—molecules essential to the function of all organisms.