Quarterary Glasiation Study Documents

QUARTERARY GLASIATION The chapter examines the Ice Age and the current interglacials during the Quaternary period. The Quaternary, from 3 million years ago to the present, witnessed the development of ice ages that came and went almost clockwise. This period is divided into the glacial epoch of the Pleistocene and the interglacial Holocene, which is also commensurate with the rise of civilization. Both Tertiary and Quaternary are terms carried over from old geologic time scales where the Primary and Secondary periods represent the history of the ancient Earth. The unequal length of the two periods is a recognition of the unique sequence of ice ages. Many geologists prefer to divide the Cenozoic into two almost equal time intervals: the Paleogene from 65 to 26 million years ago and the Neogene from 26 million years ago to the present. During the Pleistocene, the movement of continents to their current location and the increase of land to higher altitudes made geographical conditions ripe for colder climates. Variations in Earth's orbital motion may have provided an early kick to trigger the growth of continental glaciers, which partly explains the repeating of the ice age cycle every 100,000 years. Once in place, glaciers become self-sufficient by controlling the climate. Then, mysteriously in just a few thousand years, a huge ice sheet collapsed and quickly retreated to the poles. As a result of the Ice Age, many northern lands owe their unusual topography to large ice sheets washed from the polar regions. The Pleistocene, originally defined as a period of recent life based on the fossil record of modern organisms, has become synonymous with periods of glaciation that began about 3 million years ago. The Ice Age was so pervasive that ice sheets 2 miles or more thick blanketed the upper parts of North America and Eurasia, Antarctica, and parts of the Southern Hemisphere. In many areas, glaciers strip entire layers of sediment to bare bedrock, erasing the entire geological history of the region. HUMAN ERA About 3 million years ago, a massive volcanic eruption in the north Pacific darkened the skies and global temperatures plummeted, culminating in a series of glacial episodes. Climate change is driving a shift away from forest environments to open up savanna habitats in Africa.These changing conditions produced many new animal species and spurred the evolution of early humans, who had to adapt to new environments quickly. Indeed, humans are products of ice ages, which stretch throughout the human experience. Humans' direct ancestors—hominids—evolved in Africa, possibly from the same species that gave rise to great apes, including gorillas and chimpanzees. This species has 99 percent of the same genes as humans. About 7 million years ago, much of Africa entered a period of cooler, drier climate when forests retreated and were replaced with grasslands. Life in savannas, where human ancestors roamed, is harsher and more challenging than life in forests, where apes live. To survive under these difficult conditions, early humans quickly evolved into an intelligent, upright-walking species, whereas apes today are almost the same as they were millions of years ago. An early hominid species called Australopithecus (Figure 190) first appeared in Africa about 4 million years ago. It walks on two legs but retains many ape-like features, such as long arms in relation to its legs and curved bones in its hands and feet. This species was quite muscular and much stronger than modern humans. Males stand a little less than 5 feet tall and weigh about 100 pounds. The female stands about 4 feet tall and weighs about 70 pounds. Two or more australopithecine lines coexisted in Africa and survived practically unchanged for more than 1 million years. After a long period of apparent stability, all but one line went extinct, possibly due to climate or habitat change. About 2.5 million years ago, sudden climate change spurred the evolution of the first humans. The drying of the African climate led to an increase in grasslands at the expense of forests, where human ancestors probably found food, shelter and protection from predators. With the pressures of life in open savannas, early humans may have developed larger brains, which gave rise to tool-making skills and cooperative hunting techniques for survival. The most successful of the early hominids was Homo habilis, which evolved a little more than 2 million years ago. It was a species in transition between primitive ape-like hominids and early humans. His brain was about half the size of a modern human. The limb bones were very different from those of earlier hominids and more similar to those of later humans. It was the first human species to make and use tools. It had a well-developed speech center, indicating primitive language abilities. Homo habilis disappeared from Africa about 1.8 million years ago and was replaced by Homo erectus, the first human ancestor to leave Africa. The species is widely accepted as a human and appears to have evolved in Africa directly from Homo habilis. It could also have evolved independently in Asia and then migrated to Africa.About 1 million years ago, this ancient man occupied southern and eastern Asia, where he lived until about 200,000 years ago. Its advanced features indicate an acceleration of evolutionary development, as it shares many attributes of modern man. The brain was also larger, about two-thirds the size of modern humans. Many types of Homo erectus are spread throughout the world. This suggests that anatomically modern humans evolved from this species in several places, perhaps accounting for racial differences among people today. Peking man, a variety of Homo erectus that lived in China about 400,000 years ago, lived in caves and was probably the first to use fire. Another variety, called Java man, arrived in Java about 700,000 years ago. About 60,000 years ago, descendants of Javanese humans migrated to Australia and possibly other South Pacific islands. The earliest Homo sapiens were called CroMagnon, named after CroMagnon's cave in France, where the first discovery was made in 1868.They originated in Africa probably 200,000 years ago. Evidence also suggests they appeared simultaneously in some parts of the world, as much as 1 million years ago, possibly evolving directly from Homo erectus. Cro-Magnons share most of the physical attributes of modern humans. The skull, whose proportions of the brain shell is modern in structure, is short, tall and rounded. The lower jaw ends with a definite chin. The rest of the skeleton was slender and leggy compared to previous human species. Sometime in the last ice age, Cro-Magnon seems to have advanced into Europe and Asia during warm interludes when the climate was less severe. They probably lived like the natives of today's Arctic tundra, fishing in rivers and hunting wildebeest and other animals. As with the modern population of Arctic peoples, the ancestors of humans inhabiting higher latitudes were greater than those who lived near the equator. Due to the scarcity of wood in the cold tundra, ice age hunters on the plains of central Russia built houses from mammoth bones and ivory covered with animal skins (Fig. 191). They burn bone and animal fat for heat and light. Neanderthals were primitive Homo sapiens, named after the Neander Valley near Dusseldorf, Germany, where the first fossil was recognized in 1856. However, they also occupied open sites, as evidenced by hearths and rings made of mammoth bones and stone tools usually associated with these people. During the last interglacial period, called the Eemian, from about 135,000 to 115,000 years ago, Neanderthals ranged across much of western Europe and Central Asia, stretching as far north as the Arctic Ocean. Modern humans and Neanderthals seem to have coexisted in Eurasia for at least 60,000 years and shared many cultural advances. Although European Neanderthals who lived from 75,000 to 35,000 years ago were generally one-third larger than modern humans, their relative brain sizes were about the same. Neanderthals thrived in this region until about 35,000 years ago, declining over a period of perhaps 5,000 years. The disappearance of Neanderthals probably resulted from replacement or assimilation by modern humans.