MidCenozoic

The Mid-Cenozoic is a geological time period that spans from approximately 25 to 15 million years ago, marking the middle portion of the Cenozoic Era. This era saw significant changes in the Earth's climate, geology, and life forms. It is further divided into the Oligocene and Miocene Epochs, each with distinct characteristics.

During the Mid-Cenozoic, the continents began to take their modern shapes as they continued to move apart from each other. This process, known as continental rifting, resulted in the formation of various mountain ranges, such as the Sierras and the Himalayas. The Indian subcontinent, which had collided with Asia in the Paleocene, continued to push northwards, leading to a significant uplift in the region.

The Mid-Cenozoic climate was warmer and more humid than today, with no evidence of the modern-day ice ages. Forests and lush vegetation dominated the Earth's surface, and many modern-day plant species emerged during this time. The Early Cenozoic's primitive mammals, such as early horses and carnivores, continued to evolve, while modern species like early humans were nowhere to be found.

The Mid-Cenozoic also witnesses the emergence of modern coral reefs, and the "real" diversity expansion of whales, dolphins, and their close relatives, which occurred in response to changing ocean chemistries. Major world-wide ocean circulation changes also affected the geography of the oceans and helped shape coastlines.

These changes and developments laid the groundwork for the Holarctic region's unique biological and geological characteristics.