Around 15,000–20,000 years ago, as the last ice age began to recede, human populations transitioned from a way of life that depended on hunting and gathering to one that favored agriculture. This time period, known as the Neolithic period, would be marked by a sharp increase in population, increased complexity of social and political interactions, and the emergence of technology as we know it today. The era dragged along and technology slowly evolved in response to the most basic social needs of food and shelter, until about 5000 years ago when the Urban Revolution began. Before the Urban revolution, technology had existed outside the concept of "science", as it simply referred to manipulating our world (the elements, our environment, and so forth) to aid our continued survival. However, as the first astronomers in Mesopotamia--the birthplace of civilization--used data from the movements of celestial bodies to establish calendars and create irrigation systems, a creative partnership between science and technology came to the fore.