The Origin of Earth's Water and the Emergence of Life: A Comprehensive Review of Hybrid Hypotheses and Current Scientific Understanding

The origin of water on Earth and the emergence of life rank among the most fundamental and enduring questions in planetary science and astrobiology. This comprehensive review surveys the evolving understanding of how our planet acquired its vast oceans and how the earliest living systems may have arisen. We trace the shift from earlier hypotheses that emphasized comets as the primary source of terrestrial water to more recent hybrid models that incorporate contributions from asteroids, interactions with the solar wind, and intrinsic processes during Earth’s formation and early evolution. In parallel, we examine leading ideas on the origin of life, including panspermia scenarios, the role of volcanic and basaltic glass in facilitating RNA formation, and the broader implications of these mechanisms for the Fermi Paradox and the Great Filter hypothesis. Experimental and observational advances—such as laboratory evidence for RNA formation on basaltic glass surfaces, precise measurements of deuterium-to-hydrogen ratios in comets, and studies of water production driven by solar wind interactions with planetary surfaces—support a picture in which both Earth’s water inventory and the emergence of life were shaped by multiple, complementary processes rather than a single dominant mechanism. Together, these findings suggest that the conditions necessary for life may arise through a diversity of pathways, increasing the plausibility of life elsewhere in the Universe while also informing our understanding of why technological civilizations may be rare or difficult to detect.