Human civilization has developed during the Holocene epoch.
Geologists divide Earth's 4.5 billion years of history into eons, periods, eras and epochs. The current epoch, the Holocene, was preceded by the Pleistocene epoch. Sometimes also known as the ice age, the Pleistocene epoch saw the evolution of Homo sapiens, and the Holocene epoch saw Homo sapiens spread across the Earth.
Pleistocene Epoch
The Pleistocene epoch began about 1.8 million years ago. During the Pleistocene, huge sheets of ice called glaciers covered large chunks of North America, South America and Europe, all of Antarctica, and small portions of Asia. However, they would periodically recede, allowing a mild climate to develop. The glaciers reshaped the Earth's surface in many areas. They created hollows that later became lakes, turned hills into plains, and redirected the courses of mighty rivers.
Some areas, such as the Western United States, were not covered in ice. These regions experienced periods of heavy rain and decreased evaporation. These periods typically featured increases in vegetation and the formation of lakes such as Nevada's Lake Lahontan and Utah's Lake Bonneville. The original Lake Lahontan no longer exists, and Lake Bonneville is now divided into the Great Salt Lake and Utah Lake. Scientists believe that Arizona's Grand Canyon formed during the Pleistocene.
Animals
The Pleistocene is known for its wide range of now-extinct animals. These include the mastodon and woolly mammoth, giant armadillos, giant sloths, relatives of the domestic horse, relatives of the camel, and saber-toothed cats. Many species of the genus Homo evolved during the Pleistocene. The earliest members of the species Homo sapiens are held to have evolved about 500,000 years ago.
Holocene Epoch
The Holocene epoch, also sometimes called the recent epoch, began about 11,500 to 10,000 years ago. It is the current epoch. At the beginning of the Holocene, the glaciers retreated and the climate gradually warmed. However, there were some small-scale cooling periods throughout the epoch, such as the "Little Ice Age" approximately between the 13th and 18th centuries.
The warming climate encouraged many species to migrate, and some spread throughout the globe. The major event of the Holocene epoch has been the development and spread of human culture and civilization.
Human Impact
Although Homo sapiens evolved during the Pleistocene, geological evidence of Homo sapiens' impact dates back only about 10,000 years. Evidence of human activity includes leveled hills, filled-in valleys, and changes in the way sediment is deposited because of dams or diverted rivers. Archaeologists find evidence of humans adapting to their environment. For example, in Central America, evidence from the 10th and 11th centuries suggests that the Mayans abandoned many of their cities because of climate change. Around the same time, warming in the north prompted Vikings to settle Newfoundland, Greenland and Iceland.
According to the University of California Museum of Paleontology, humans have affected the environment more than any other species has. For example, pollution and habitat destruction have caused mass extinctions, while human-caused global warming has raised the atmosphere's temperature.
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