Geoscience Reference
In-Depth Information
Now
5%
Eccentricity
Past
Future
3%
Precession
+
1%
-
Tilt
24.0
°
23.5
°
23.0
°
22.5
°
-250
-200
-150
-100
-50
0
+50
+100
Ky
BP
Ky
AP
Fig. 1.20
Orbital wobbles due to variations in planetary eccentricity, precession, and axial tilt as hindcasted and forecasted by astrophysicists.
Note that our immediate future looks a little less “wobbly.”
1.6.8
Dangers of correlating xwith y
(b)
In mathematics, two variables can exist such that the value
of
y
depends
exactly and only
on the value of
x
(in short-
hand,
y
(a)
x
2
; a cue to consult our excellent
Math appendix). In the natural world, correlation is less
than perfect and certainly does not identify cause and
effect. Thus highly correlated plots of increased atmos-
pheric CO
2
against increasing mean global temperature do
not
a priori
imply that the CO
2
is
causing
the positive cor-
relation: some other factor may be involved, for example,
increase in CO
2
may be the
result
of temperature increase
caused by something else (e.g. variations in solar output).
Keep your mind open.
f
(
x
), as in
y
Flow
Fig. 1.21
Only flows over rotating spherical curved surfaces are devi-
ated due to gradients in spin. (a) Sphere: spin variable, flow deviated
and (b) cylinder: spin constant, no deviation.
Further reading
R. A. Bagnold's somewhat varied career is described in his
autobiography,
Sand, Wind and War
(University of
Arizona Press, 1991). Much of interest in comparative
planetology is in R. Greeley and J. D. Iverson's
Wind as a
Geological Process
(Cambridge, 1985). Aspects of Earth
measurement may be found in K. Ferguson's
Measuring
the Universe
(Headline, 1999), S. Pumfrey's
Latitude and
the Magnetic Earth
(Icon, 2002), D. Sobel's
Longitude
(Fourth Estate, 1996), and G. Menzies' superb account of
medieval Chinese navigation,
1421
(Bantam, 2002). The
story of mid-ocean ridge vents and their associated life
forms is beautifully told in C. L. Van Dover's
The Octopus's
Search WWH ::
Custom Search