The Quaternary Period is the most recent period in Earth's history, lasting from about 2.6 million years ago until now. It's part of the Cenozoic Era, which started around 66 million years ago after the age of dinosaurs (the Mesozoic Era). The Quaternary Period has been marked by the development of the polar ice caps, the appearance of modern plants and animals, and the evolution of humans. The earth has gone through a number of climate changes during this time, including the growth and melting of glaciers. These climate changes have affected the spread of plants and animals and the evolution of human societies.