Sharks, living in the ocean, are fish in the ocean. Sharks existed on Earth 300 million years before the appearance of dinosaurs, and have been more than 500 million years old. They have hardly changed in the past 100 million years. Sharks, known in ancient times as crickets, scorpion sharks, and sand fish, are giants in the ocean, so they are known as "wolves in the sea." The traditional idea is that the protein in the shark's cartilage (ie shark's fin) is high, but this is wrong. Egg protein far exceeds shark fin. In addition, studies have shown that because sharks are prone to enrichment of mercury, while shark fins contain a certain amount of neurotoxins, they are potentially harmful to humans. Because of the large number of huntings in decades, sharks are at risk of extinction.