can there are only terrestrial creatures instead of having aquatic creatures existing on the earth

In a theoretical scenario where only terrestrial creatures existed and there were no aquatic creatures on Earth, the planet's ecosystem would be fundamentally altered in numerous and profound ways:

1. Ecosystem Structure: The absence of aquatic ecosystems would mean a significant reduction in the variety of habitats available for life. This would eliminate the unique environments offered by oceans, rivers, lakes, and wetlands.

2. Biodiversity Loss: Aquatic species constitute a substantial portion of Earth's biodiversity. Without these species, there would be a massive loss of genetic diversity and a simplification of the planet's ecological complexity.

3. Food Web Disruption: Many aquatic organisms are primary producers or form the base of aquatic food chains. Their absence could lead to a collapse of the food web in water bodies, affecting species that rely on these resources either directly or indirectly.

4. Human Impact: Human societies rely on aquatic ecosystems for food, employment (fishing industries), recreation, and cultural significance. The absence of aquatic life would have profound social and economic impacts.

5. Water Cycle Alterations: Aquatic organisms play crucial roles in the water cycle, such as contributing to nutrient recycling and carbon sequestration. A world without them might experience different patterns of nutrient cycling and climate regulation.

6. Migratory Species: Many species rely on both aquatic and terrestrial environments at different stages of their life cycles. In a world without aquatic creatures, migratory species that depend on water bodies for part of their lifecycle would face significant challenges or might not exist at all.

7. Planetary Atmosphere: Aquatic ecosystems contribute significantly to the global carbon cycle, acting as carbon sinks. The absence of these ecosystems could alter the balance of gases in the atmosphere, potentially affecting climate patterns.

8. Evolutionary Implications: Terrestrial creatures that evolved from aquatic ancestors might develop differently or not at all if aquatic environments did not exist. The evolutionary tree of life would likely be very different.

9. Habitat and Resource Competition: With no aquatic habitats, competition for limited terrestrial resources could become more intense, potentially leading to changes in species distribution and population dynamics.

This hypothetical scenario underscores the interdependence of aquatic and terrestrial ecosystems. The reality is that Earth's ecosystems are intricately linked, and the absence of one would inevitably and dramatically affect the other. Life on Earth has evolved to thrive in a wide range of environments, and the coexistence of both aquatic and terrestrial creatures is a testament to the adaptability and resilience of life.