The Quaternary Period follows the Tertiary Period of Geological time. The era ranges from 1.8 million years ago to the present. However, the exact age is highly debated and variable (some sources go back 5 million years). The Quaternary Period is most noted for its intervals of glacial and interglacial ages as well as the emergence of man. The Quaternary Period (aka the Great Ice Age) is subdivided into the Pleistocene Epoch (1.8mya-10,000 years ago) and the Holocene Epoch (10,000ya-present). The two subdivisions are distinguished by the most recent glaciation period.
The climate of the Quaternary period showed several decreases in global temperature (glacial periods) separated by warm (interglacial) periods. Core samples taken from sea beds elude to at least sixteen glaciations during the Quaternary period. The current warm and ice free conditions of the Holocene Epoch may be a result of the end of the last glaciation or the climate may be a part of an interglaciel period.
The constantly changing climate of the Quaternary period resulted in some environmental changes. Changes in the amounts of rainfall during the Great Ice Age corresponded with the cyclic changes in the environment. These changes in rainfall were important in tropic and subtropic regions of the globe because of the resulting shift in bondries between tropical forest, savanna and arid vegetation zones. In areas where glaciers were progressing and receding plants and animals were displace be the ice, migrating to warmer areas as the ice sheets advanced. Plant and animal life was essentially the same during the early Quaternary Period as it is today accept for the presence of the megafauna such as mastodons which have since become extinct.
During the Great Ice Age the land masses of Earth had achieved the basic shapes and global positions in which we see them today. During the Quaternary period, glacier ice was spread over more than 1/4 of the land surface of the planet. Glaciers were located from Canada to the Southern United States, Siberia, in addition to a European system. The cycle of glacier melting in forming resulted in the rise and fall of the world's water levels. One of the highest rises in sea levels is believed 30 meters above its present level and the lowest extreme being 80 meters bellow the present sea level. In other words, though the continental positions are relatively the same as they are today, the geography of the period was very variable as a result of the rapid variation in sea levels caused by the fluctuation of ice sheets.
The Quaternary Period allowed for rapid evolutionary advances as a result of adaptive radiation stimulated by the extreme climatic and environmental changes. Adaptive radiation is the continual multiple speciation from one common ancestor. The Quaternary period displays high rates of evolution particularly among mammals. The movement of glaciers resulted in the migration of vegetation and animals allowing for the colonization and saturation of new areas. The inhabitation of new areas by new species further encouraged adaptive radiation.
By the end of the first half of the Quaternary Period many species of mammals had become extinct in sections of the Earth. The llama, camel tapir, horse and yak became extinct in North America but were still found inhabiting other areas of the globe. Large mammals such as the mastodon, saber-toothed tiger, ground sloth became extinct everywhere during this period. The complete extinction of these mammals may have resulted from climactic changes or the large mammals may have been hunted to extinction by early man. The larger animals may have felt the affects of these influences more than other smaller species because the giant mammals may have reproduced more slowly and were unable to recover their numbers. The two factors combined were probably enough to over-stress the animals leading to their extinction.
The year 1829 saw the discovery and naming of the Quaternary Period by French geologist Jules Desnoyers. Originally believed to be a result of Noah's biblical flood, the era was named after the sedimentary and volcanic deposits (very few fossils) in the Seine Basin in northern France. In 1839 a Scottish geologist, Charles Lyell, divided the Quaternary Period into the two subdivisions of Pleistocene and Holocene eras. Currents study of the period is done in areas such as the Great Salt Lake and the Great Lakes to form more concrete ideas in regards to glacial movement. The fossils documenting the emergence of man are primarily studied in Africa, but are also studied in places such as Nova Scotia where evidence of the migration of modern man date as far back as 12,000 years ago. Some of the most highly noted researchers of homonids Louis and Mary Leakey and their son Richard.