This upload contains a hypothesis paper proposing the Snow Hypothesis: a thermal-gradient surface conveyor that couples atmospheric ice photochemistry to prebiotic assembly on the early Earth. The mechanism separates synthesis, mixing, concentration, catalysis and a route to homochirality into hot, warm and cold-edgezones connected by downhill meltwater flow and the water cycle. The paper does not report new experimental results. It develops a conservative order-of-magnitude framework and proposes falsifiable experiments, with the contact-film thermal window identified as the central physical test. An English version and a Russian translationare included. This is a preprint / hypothesis paper and has not undergone peerreview.