An ancient geological turnstile
The Turgai Gates owe their existence to water. For over 130 million years, from the Middle Jurassic to the Oligocene, a vast, shallow inland sea called the Turgai Sea separated Europe from Asia. This epeiric sea extended from the ancient Tethys Ocean north to the paleo-Arctic, effectively making Europe a large island archipelago. Animal populations on the two landmasses evolved in isolation. The final retreat of this sea, which concluded around 29 million years ago, exposed the Turgai Basin—a low-lying depression between the Ural Mountains to the west and the Kazakh Uplands to the east. This new stretch of land became a natural corridor for life to cross between continents.
The corridor was not permanently open. Its accessibility depended on the planet's shifting climates. During warmer, wetter periods, forests expanded and the corridor may have been less suitable for grassland species. In colder, drier times, including the Pleistocene ice ages, the steppe environment expanded, creating a more inviting route for megafauna adapted to open plains. Fossil pollen analysis provides a detailed record of these environmental shifts, allowing scientists to correlate the vegetation with the types of animals making the journey. The opening of the corridor around 12 million years ago during the Miocene Epoch triggered a significant faunal interchange.