Earth May Have Been Seeded with Life

Earth formed about 4.5 billion years ago. Life appeared early in the planet's history, yet there is still no complete chain from inorganic chemistry to the first cell. In 1953, Stanley Miller and Harold Urey sent electric sparks through gas and water and made amino acids. They made ingredients for proteins, not life.

Miller and Urey made ingredients for proteins, not a living system. To become life, those molecules still need a boundary so they do not disperse, a source of energy, a way to keep instructions, and a way to copy those instructions reliably enough to change over generations. Hydrothermal vents, drying ponds, mineral surfaces, and even space have all been proposed as places where early steps could happen. No model has joined every step.