do aquatic creatures completely disappeared after the appearance of terrestrial creatures

No, aquatic creatures did not disappear after the emergence of terrestrial creatures. The evolution of life on Earth occurred over a vast timeline, and aquatic life forms have existed for billions of years before and alongside the development of terrestrial life.

Here are some key points to understand this:

1. Early Life Originated in Water: Life on Earth is believed to have originated in aquatic environments, such as oceans, around 3.5 to 4 billion years ago. These early single-celled organisms evolved and diversified in water long before any life forms ventured onto land.

2. Evolutionary Timelines: The first evidence of simple, multicellular life forms appears around 2.1 billion years ago, still entirely aquatic. The colonization of land by plants and animals (known as the Paleozoic陆地化) happened much later, approximately 500 million years ago during the Silurian period.

3. Coexistence: Terrestrial life forms and aquatic life forms have coexisted since the advent of terrestrial life. They are not mutually exclusive; both environments support a wide range of life forms that continue to evolve independently but also interact in various ways.

4. Diversity: Both aquatic and terrestrial ecosystems have continued to diversify and expand since the appearance of land-based life. There is a rich variety of species in both realms that are adapted to their specific environments.

5. Continuing Evolution: Aquatic species have not only survived but also continued to evolve and adapt to their environments. For example, marine mammals like whales and dolphins evolved from terrestrial ancestors that returned to the water.

6. Interactions: There are many examples of interactions between aquatic and terrestrial ecosystems, such as rivers and streams connecting land to the sea, or birds that fly between land and water bodies.

In summary, the emergence of terrestrial creatures did not lead to the disappearance of aquatic creatures. Instead, both aquatic and terrestrial life forms have continued to evolve and diversify, forming complex ecosystems that coexist and interact in many ways. Life on Earth is a tapestry of interwoven aquatic and terrestrial ecosystems, each with its unique set of species and ecological dynamics.