GEOLOGY

Detailed explanation-1: -The first fish appeared around 530 million years ago and then underwent a long period of evolution so that, today, they are by far the most diverse group of vertebrates.

Detailed explanation-2: -The earliest fish, resembling living hagfish, evolved about 550 million years ago. Adaptations that eventually evolved in fish include a complete vertebral column, jaws, and an endoskeleton made of bones instead of cartilage. Fish live throughout the ocean and in freshwater lakes and streams.

Detailed explanation-3: -From an explosion of early life to the greatest extinction in history, the Paleozoic was a time of change. During this earliest era, living things developed vertebral columns and hard body parts like jaws, bones and teeth. Fish evolved, and plants and animals started the move from the ocean onto dry land.

Detailed explanation-4: -Most important for the evolution of fishes and vertebrates in general was the early appearance of bone, cartilage, and enamel-like substance. These materials became modified in later fishes, enabling them to adapt to many aquatic environments and finally even to land.