Panspermia

Panspermia boldly asserts that life on Earth arrived via bacteria-laden comets or space dust, challenging the dominant abiogenesis narrative championed by less contrarian theories. Fred Hoyle and Chandra Wickramasinghe's 1970s calculations showed that interstellar dust grains could shield microbes from UV radiation for up to 1 million years, making interplanetary travel plausible. Yet a 2022 study on Earth's earliest fossils, dated at 3.5 billion years, found that 90% of their organic markers are consistent with local synthesis rather than extraterrestrial origin. This data point undercuts panspermia's core claim, making it 25% less accepted than punctuated equilibrium (#4) among astrobiologists. Compared to string theory (#2), panspermia at least offers a testable prediction: if life is cosmic, similar signatures should exist on Martian meteorites—a hypothesis awaiting verification from current sample-return missions.