the hydrothermal vents were a relic environment, one we believe resembles what the early conditions on Earth might have been. What we’re doing ultimately is trying to understand how life evolved on the planet. For all of their extremes of temperature, pressure, and other properties, deep-sea vents may have offered a relatively cozy refuge on the violent world of the early Earth. Our young planet was bathed in much stronger ultraviolet radiation from the sun because it hadn’t yet developed a protective ozone layer. That didn’t come along until after the evolutionary invention of photosynthesis pumped a steady supply of oxygen into our atmosphere. One big attraction is the presence of an ion gradient—a key ingredient in just about every known form of life—between the vent fluids and the seawater. The alkaline fluids are basic, with a pH (a measurement of acidity and alkalinity levels) of around 10 or 11, meaning they have a low concentration of protons. Seawater, with a pH of around 8, is less alkaline—that is, slightly more acidic—so it has more protons than the vent fluids. The vent would have acted as a natural hydrothermal reactor. Reactions between carbon dioxide and hydrogen, catalyzed by minerals found in the vents, can form a molecule known as pyruvate. Pyruvate is a precursor of many amino acids, which in turn can link together to create proteins.

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