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Chapter 07
Ancient Tibet - History and Culture Though glaciers across the plateau were decreasing, permafrost became widespread. In this condition, the soil itself freezes and remains frozen for at least a year at a time, except for a thin layer on the surface that may melt during the summer months. The last major advance of the ice began 72,000 years ago. In the Far East, the onset of this cold period commenced about 70,000 years ago. About 58,000 years ago, a mild interlude took place, although this is not yet well documented for Tibet. The climate turned severely cold 28,000 years ago, becoming even harsher than the previous cold period. By 18,000 years ago, the ice reached its maximum.
The Theory of Evolution
CENOZOIC
MESOZOIC
3.5 billion
years
ago:
1st life
PALEOZOIC
4.5 billion
years
ago: earth forms
PRECAMBRIAN
Fish
Sponges
Arthropods
Coral
Brachiopods Echinoderms
Molluscs
? ? ? ? ? ? ?
Algae and Single-celled Organisms
400
500
600
100
200
300
Millions of years ago
According to the theory of evolution, different life forms arose at different times. Single-celled plants and animals arose first; they gave rise to more complex forms, such as corals, worms, sponges, and seaweed. More advanced animals began to emerge by 450 million years ago. The earliest fish first animals with a backbone were followed by amphibians and reptiles. From a branch of the reptile line, mammals arose 200 million years ago. Among the mammals were the primates, which eventually gave rise to humans.
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Ancient Tibet
