is the possibility very low of terrestrial creatures completely replace all aquatic creatures

Yes, the possibility of terrestrial creatures completely replacing all aquatic creatures is extremely low due to several fundamental reasons: 1. **Unique Adaptations**: Terrestrial and aquatic creatures have developed unique adaptations that make them suited for their specific environments. Aquatic creatures are specifically adapted to live in water, and their replacement by terrestrial creatures with different physiological needs is highly improbable. 2. **Different Environments**: Terrestrial and aquatic habitats have vastly different conditions regarding physics (e.g., gravity, buoyancy), chemistry (e.g., dissolved gases), and biology (food chains, predator-prey relationships). organisms evolving one into another would require adapting to entirely new sets of environmental challenges that cannot be bridged easily across two vastly different ecosystems. 3. **Evolutionary Process**: Evolution occurs over millions of years and is driven by natural selection, mutation, migration, and genetic drift, rather than intention or conscious design. It tends towards specialization as species adapt to their specific niches rather than toward broadscale replacement. 4. **Divergently Specialized Ecosystems**: The Earth’s ecosystems are inextricably interlinked. Inaquatic environments, evolutionary changes often create highly specialized predators, prey, symbionts, and decomposers. These ecological dynamics cannot be simply mirrored or replaced by generically adapted terrestrial organisms. 5. **Environmental Gradient**: Terrestrial and aquatic environments form a gradient, not a boundary, where different species and subspecies gradually adapt along successive environments from land to freshwater to saltwater environments. A complete shift would disrupt the gradient rather than usefully recreating it. 6. **Extinction Events**: For terrestrial species to replace aquatic ones, extinction-level events would effectively need to wipe out existing aquatic creatures—events that also cause massive global disruption and affect terrestrial life as well. 7. **Genes and Developmental Biology**: Aquatic species have unique genetic codes and developmental sequences that cannot magically evolve into those of terrestrial species—even if there were no environmental pressures tying aquatic creatures to their habitat, the developmental processes would provide barriers. In summary, given the current understanding of biology and evolution, such a scenario would defy most known principles of how species adapt and evolve and is consequently considered practically impossible under normal circumstances.