Our ancestors used volcanic glass known as Obsidian from about 12,500 B.C.E. until roughly 4000 B.C.E., but the Age of Obsidian really ended around 8000 B.C.E. At that point, humans along the Yangtze, Indus, Tigris, Euphrates, and later the Nile river valleys developed agriculture. The world changed when humans learned to grow their own crops.
The Age of Obsidian was marked by small bands of nomadic, semi-nomadic, and occasionally sedentary people roaming the world in search of food or tracking herd migrations. There was no knowledge of the male involvement in reproduction, so instead the woman's ability to spontaneously create life was seen as magical. Women weren't seen as superior to men, though. Both sexes had their respective places in society and were equally respected.
In 12,500 the world was still in the middle of the last ice age. Half the planet was buried under ice, while the other half was enduring heat waves. Vegetation was scarce so animals had a hard time surviving. Many didn't make it, so the period from 12,500 until about 10,000 B.C.E. was a major extinction event. The Neanderthal, Mastodon, Mammoth, and Giant Anteater all disappeared at this time.
Around 10,000, the glaciers started to recede. Some of the modern seas were formed at about this time. The Mediterranean had been two inland seas during the ice age, but when enough ice had melted a tidal wave swept over the land between the Atlantic and the modern Mediterranean and flooded everything. That's why so many myths in the Mediterranean involve a great flood.
The last main happening of the period occurred in 8000 B.C.E. At that time, humans discovered that the grains wheat and rice were not only edible, but they provided many calories and were easily farmed along the river valley. The discover would lead to the first villages, forever changing human society and exploding its population.
The period was noteworthy in most of the world for its nomadic nature; up until 8,000 B.C.E. only groups fortunate enough to have found a valuable natural resource such as obsidian or fish were able to settle. All other persons migrated regularly. Some tribes followed herds while others would move from valley to valley exhausting the local flora and fauna as they went.
During the Age of Ice, people had been forced to survive on gathering and hunting, and because of their primitive tools they hadn't been able to make life much easier for themselves. The invention of the awl, hand axe, and needle made it easier to make clothes. Bolas, the Bow and Arrow, the Fish Hook, Harpoon, Microlith or very small tools, Net, and the Spear Thrower made hunting easier, and both Pressure Flaking and Scraping made it possible to create the new tools.
No one knows exactly when they started, but the people of the Age of Obsidian used a Lunar Calendar to mark time. For them, thirteen lunar months (361 days) marked a full year.