>Question 1: My Norwegian astrophysics textbook says the period of the
>earth's precession is around 23000 years. Is the point then that 12000 is
>about 50% of 23000, or is something very wrong here?
I finally chased this down. Hayward cites Bradley's 1929 article on the
Green River, "Climate of the Green River Epoch, USGS Prof. Paper 158,
(1929), p. 87-110. Bradley's table on page 105 shows that there is an
alternation of oil shale and marlstone. Based upon the thickness of the oil
shale and marlstone beds and average laminae thickness, Bradley shows that
each lithology takes around 10,000 years (on average) to be deposited.
Hayward grabbed a half cycle number rather than the full cycle. The total
cycles given by Bradley (1 oil shale + 1 marlstone ) are:
26,500 years
25,200 years
22,800 years
27,000 years
18,500 years
23,200 years
16,530 years
25,350 years
22,700 years
21,000 years
19,500 years
18,600 years
21,600 years
21,000 years
20,500 years
16,100 years
Average length of cycle 21,630 years.
The only thing resembling a 2000 year cycle I can find is the mean
accumulation time per foot. But that is not a cyclicity.
glenn
Adam, Apes, and Anthropology: Finding the Soul of Fossil Man
and
Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm