Sharks first appeared over 400 million years ago and swam the ancient oceans long before trees grew on land. Early sharks like Cladoselache had torpedo-shaped bodies built for speed in nutrient-rich waters. The first true trees appeared around 350 million years ago, with species such as Archaeopteris showing features of both ferns and modern trees. Life on land was harsh, with intense UV radiation and wild temperature swings, while the seas offered a stable environment. Sharks have survived five