Final answer:
A major climatic change began to occur 5-7 million years ago, triggering the cooling of Earth's climate, leading to the Quaternary Period's ice ages. This coincided with the drying of African environments, which pressured early human populations to adapt and ultimately migrate out of Africa. The event contributed significantly to the evolutionary trajectory of Homo sapiens and their global expansion.
Step-by-step explanation:
Between 5-7 million years ago, a major climatic change occurred which led to the Earth's climate cooling, marking the beginning of the Quaternary Period. This cooling was characterized by the onset of ice ages and significant changes in sea levels due to the formation of glaciers. The trigger for a series of transformative environmental and evolutionary events was the drying of the African environments, prompting changes in the flora and fauna that sustained early human populations. The drying of Africa led to adaptations in hominid species, eventually contributing to the migration of Homo sapiens out of Africa and their global expansion, taking advantage of lower sea levels to move across continents.
In the Tertiary Period that preceded it, the Earth's climate was warm and humid, which was ideal for the evolution of various mammalian species. However, as the climate shifted during the Quaternary Period, many species, including some hominids, had to adapt or face extinction. These adaptations were a crucial part of human evolution and migration. The African drying trend became particularly influential, acting as a pressure that pushed early Homo sapiens to explore and settle in new territories.