Now, since there are (as Tsuguhito Takeuchi has previously pointed out) significant differences in style in the manuscripts written after the fall of the Tibetan empire, we should be able to use this typology to help decide whether an undated manuscript was written during the time of the Tibetan empire, or later.
So the second part of the article looks at the post-imperial styles, which are much more varied, as one would expect when the imperially standardised systems of teaching writing had broken down.
Thus we end up placing these manuscripts in time spans that may be much wider than we would like.
In the case of the Tibetan manuscripts from the sealed cave in Dunhuang, the range of possible dates begins with the Tibetan conquest of Dunhuang (786/7) and continuing to when the cave was sealed at the beginning of the eleventh century.
For the seclusion and different plateau climate from the inner land, the Tibetans used their own wisdom to explore astronomic changes in their productions and daily life, and finally created a rough series of rules as their guide.
Before 100 BC, the indigenous religion of Tibet - Bon marked off months according to the circle of changes of the moon.
They also extracted some ideas from the Indian Calendar when Buddhism was introduced from there.
Older known human camps do exist in the region, dating to between 9,000 and 15,000 years ago, but they were likely short-term, seasonal sites, the researchers said.
[See Photos of Chusang, the Oldest Known Site Occupied Year-Round on the Tibetan Plateau] "Chusang is special because you have these human footprints in this carbonate mud," said study co-lead researcher Michael Meyer, an assistant professor of geology at the University of Innsbruck in Austria.
The 19 human handprints and footprints were found near Chusang, a village known for its hydrothermal springs, located on Tibet's central plateau at an elevation of about 14,000 feet (4,300 meters) above sea level.
A previous attempt to date the prints estimated that they were 20,000 years old, according to a 2002 study published in the journal Geophysical Research Letters.