Introduction:
The Old Stone Age, also known as the Paleolithic period, refers to the earliest and longest period of human history. It is characterized by the use of stone tools and the development of early forms of hunting, gathering, and social organization. In this period, early humans were primarily nomadic and relied on hunting animals and gathering wild plants for survival.

Key Point:
The Old Stone Age began approximately 2.5 million years ago.

Explanation:
1. The Old Stone Age is divided into three main phases: Lower Paleolithic, Middle Paleolithic, and Upper Paleolithic. Each phase represents a different stage of technological and cultural development.
2. The Lower Paleolithic, the earliest phase of the Old Stone Age, began around 2.5 million years ago and lasted until approximately 300,000 years ago.
3. During this time, early humans, known as Homo habilis and Homo erectus, began to use simple stone tools such as hand axes and cleavers. They also started to control fire, which provided warmth, protection, and a means to cook food.
4. The Middle Paleolithic, which followed the Lower Paleolithic, began around 300,000 years ago and lasted until approximately 30,000 years ago.
5. This phase is marked by the emergence of the Neanderthals (Homo neanderthalensis) and the development of more sophisticated stone tools, such as spear points and scrapers.
6. The Upper Paleolithic, the final phase of the Old Stone Age, began around 50,000 years ago and ended around 10,000 years ago.
7. During this period, anatomically modern humans (Homo sapiens) appeared and demonstrated advanced tool-making skills, art, and symbolic behavior.
8. The Old Stone Age finally came to an end with the advent of the Neolithic Revolution, which marked the transition from hunting and gathering to agriculture and the domestication of plants and animals.

Conclusion:
The Old Stone Age, or Paleolithic period, began approximately 2.5 million years ago. It was a time of significant cultural and technological development, characterized by the use of stone tools, the control of fire, and the emergence of early human species. The Old Stone Age laid the foundation for the subsequent development of human civilizations.