The Oligocene is a geological epoch that lasted from about 34 to 23 million years ago. It is part of the Cenozoic Era and follows the Eocene epoch. During this time, the Earth's climate began to cool, leading to the development of grasslands and the expansion of mammals. Many modern mammal families, such as horses and whales, began to evolve during this period. The Oligocene is characterized by significant geological changes, including the formation of mountain ranges like the Himalayas and the Rocky Mountains. These changes influenced global climate patterns and ocean currents. Fossil records from the Oligocene provide valuable insights into the evolution of life on Earth, showcasing a diverse range of flora and fauna.