Times early civilizationprt

Slide1: 

In the Times of early civilizations- The warmest post-glacial times: development of the deserts of Asia and the river valley civilizations. Civilizations organized at about 5000 years ago in the Tigris and Euphrates lowland, in the Indus Valley, and in China were at least in part a necessary development to feed a more concentrated population at a time when huge areas outside those valleys in Arabia, in Afghanistan and Rajastan, and in the Gobi and Sinkiang, were becoming more desert-like. As pastures and stocks of wild game for hunting were failing, the advantages of cultivation in more or less reliably irrigated valleys would become obvious to those faced with abandoning an older way of life. The warmest post-glacial times: development of the deserts of Asia and the river valley civilizations. The Japanese meteorologist Hideo Suzuki has made to the interesting suggestion that it was the refugee herdsmen and farmers from the increasingly desert regions who were fated to become the slaves who made possible the intensive agriculture and the great building works for which ancient Egypt and the other river valley civilizations are famous. Sea level was possibly highest at about the end of the warmest climatic regime, when the melting of glaciers was complete. The first canal built to link the Mediterranean and the Red Sea at Suez, actually a fresh water canal from the Nile Delta to where the Suez canal stands, was started in the 20th century BC under pharaoh Sesostris I, about the time when world sea level was probably just at its highest. This project was feasible because the land barrier would be shortest when sea level was highest. Sea level probably remained this high for several centuries afterward, beginning to fluctuate more after 1600 BC. A second Suez Canal, or possibly a reconstitution of the first one dates from Rameses II (1304-1237 BC), whose reign seem so of been in one of the last of the fairly prolonged and spells of full warmth of the warmest post-glacial times. Rameses’ reign was responsible for many of the great temples and art works of Egyptian history. It is also important to know that Rameses II fame was in large part due to his propaganda machine…and he lived to be 93 years of age when most people died in their 30s. It may be that the escape of the early Israelites out of Egypt at about 1230 BC, described an exodus, is explained by short-term fluctuations of the Red Sea waters (as with a storm surge or tidal wave) over the shallow sands at a time when the sea was normally higher than now. Reconstruction of the prevailing atmospheric circulation during each of the main stages of post glacial climate history produces a record of the probable latitude of the North Atlantic North European storms zone (the concentration of paths of the low pressure centers ) and of the Azores-European-North African anti cyclone zone that runs a broadly parallel to the prevailing temperatures. These indicate that summer monsoon rains penetrated much farther north than now over the Sahara region. It seems likely that occasional cyclonic activity from the south could have reached across what is now the desert to the Mediterranean in the summer during the warmest post glacial times. With this pattern there could be easily and of vegetation and surface water in the Sahara for people and animals and explain the much larger size of Lake Chad between 7000 BC and 3000 BC. Estimates of the average annual rainfall in the Sahara center between Kufra and Tibesti, which at present seldom see any rain, range from 200 to 400 mm before 6000 BC and 50 to 150 mm towards and 3000 BC, and in the region of Lake Chad near the edge of the Sahara two to five times and these amounts.

Slide2: 

The water level in Lake Rudolf and other East African lakes was several tens of meters higher than now and overflowed into the Nile. The Sahara desert before 3000 BC was probably a dry Savannah with trees along the permanent or nearly permanent rivers. There is evidence that this moisture was interrupted for a little less than a thousand years just before 5000 BC. This seems to coincide with the entry of the sea into Hudson bay, followed by the rapid degeneration of the Laurentide ice sheet: an event that probably distorted the hemisphere's thermal and wind patterns. A more serious break in this climatic regime came between 3500 and 3000 BC there was at least one fluctuation in that interval of greater magnitude than had occurred in a very long time. The glaciers in the Alps advanced and the forest retreated from the heights: this is called the Piora oscillation, named after the Val Piora where the first evidence was found an established by pollen analysis indicating a cold period. In the temperate forest zones all over Europe and parts of North America and elm and linden trees declined and never regained their former dominant position in the forests. The duration of this cold episode seems to been quite short, at most four centuries, but traces of it extend to Alaska the Colombian Andes and the mountains of Kenya. This was evidently a global disturbance. It marked the end of the most stable warm climate of post-glacial times, a regime which had been associated with greater prevalence of westerly winds in middle and sub Arctic latitudes. That regime is referred to, in order European literature as the 'Atlantic' climate period (now defined as ~8000-4500BP). With prevailing mild winters and warm summers and with the storm belt so far to the north, mean temperatures in Europe seem to have been up to two degrees higher than in recent times. Most of the world in fact seems to of been almost that much warmer.