February 2017 - The Quaternary period, which began about 1.8 million years ago (1,800,000 years ago), is still going on today - we live in the Quaternary period. So far, it's a much shorter period than the others.
At the beginning of the Quaternary period, early people in Africa were already using stone tools. The climate was mostly on the cooler side, with ice ages coming and going every forty thousand years or so. There were big ice caps at the North and South Poles, as there are today. Among the bigger mammals were saber-toothed tigers, mammoths and mastodons, small ancestors of horses, and wolves.
A million years later, about 800,000 years ago, people began using fire to cook their food. These people probably gathered berries and roots and grains, and scavenged meat left over by other animals. By about 400,000 years ago, people had divided into two or more groups - one was the Neanderthals, and another was our own ancestors, homo sapiens. By 350,000 years ago, some Neanderthals had left Africa and were living in West Asia and Europe. About 200,000 years ago, people in East Africa were trading obsidian as far as a hundred miles away.
By about 180,000 years ago, an Ice Age may have caused some people in Africa to begin to wear clothes. By 64,000 years ago, they had invented the bow and arrow. About 60,000 years ago, probably drawn by changing climate at the end of another Ice Age, some modern people left Africa and traveled along the coast of South Asia into India and then over to Australia. A little later, other people moved out of Africa north into West Asia and then into Europe, Central Asia and China. These people lived alongside the Neanderthals for a while, but by about 30,000 years ago all the Neanderthals had died out, perhaps killed off by our ancestors or by sicknesses and tapeworms carried by our ancestors, or possibly by cold weather.
From 22,000 to about 16,000 years ago, there was another Ice Age, which caused more human migrations. In Europe, people moved south into Spain and Italy. From Central Asia, people moved south on to the Deccan Plateau in central India. Other Central Asian people may have used the land bridge that appeared at this time to cross over from East Asia into North America (or they may have traveled along the coast by boat).
About 12,000 years ago, the end of this most recent Ice Age left Earth in a time when it was warmer than usual and wetter, and everything grew really well. Many large mammals that were adapted for the cold died out, maybe because of the climate; more likely because people hunted them to extinction. The animals that disappeared included saber-tooth tigers, mammoths, and mastodons. In North America, horses, camels, and cheetahs died out too, but horses lived on in Central Asia and camels survived in South America. Other animals like cattle, goats, wolves, and dogs did fine. Probably because of the warmer, wetter climate, there was enough food available in many places that some nomadic hunter-gatherers settled down in one place and just got their food there. Soon afterwards, these people began to grow their own food - that was the beginning of farming.
The first farmers may have been in West Asia, but people were soon farming in Africa, China, and South America too. Farmers could feed a lot more people, but they had to defend their land from other people. They began to have a lot of children, to use as soldiers, and by 6000 years ago people were beginning to live in cities in Asia, Africa, and South America. Since then, farming and cities have gradually spread around the world, to Europe, then to North America, and finally to Australia. Today more than half the people in the world live in cities, and more people leave the country and move to cities every day.