1. The Quaternary Ice Ages: This is a series of glacial and interglacial periods that began approximately 2.6 million years ago and continue to this day. These ice ages were characterized by significant global cooling, the expansion of ice sheets, and the lowering of sea levels. This had a profound impact on the Earth's environment and the evolution of life, including the extinction of many megafauna species and the development of human civilization.

2. The Rise of Homo sapiens: This occurred approximately 300,000 years ago during the Pleistocene epoch. Our species emerged during the Quaternary Period and eventually spread across the globe, leading to the development of diverse cultures and technologies. This event has fundamentally shaped the course of human history and the relationship between humans and the environment.