Isn't it interesting to note the following about the strength of the Earth's magnetic fiel
> Isn't it interesting to note the following about the strength of the
> Earth's magnetic field:
> 8000 bC 98 Gauss
> 6000 bC 35 "
> 5000 bC 20 "
> 4000 bC 12 "
> 1970 AD 0.62 "
(I) IS THERE SOMETHING WRONG WITH THESE NUMBERS?
These numbers are identical to those proposed by creationist Thomas
Barnes for his "magnetic field decay" idea, as published in an
Institute for Creation Research Technical Monograph called _The Origin
and Destiny of the Earth's Magnetic Field_. Barnes's assumptions are,
um, rather unique. It is safe to expect that Mr. Kiledal is working
from either Barnes directly or from a source which presents Barnes's
data uncritically. It is highly unlikely that someone else independently
arrived at identical numbers.
Kiledal presents these numbers as if they were factual, but that is
not even close to the truth. The only number in Kiledal's list which
is even remotely connected with any physical measurement is the number
presented for 1970 AD. Barnes's data extends back to about 1820 AD,
and every value previous to that  i.e., every other data point that
Kiledal mentions  is based on an unjustified exponential extrapolation
from the recent values. (Erik may not have been aware of this if his
source doesn't present how Barnes arrived at his numbers.)
Barnes's data rests on the following untenable assumptions:
1) Exponential extrapolation is justified far beyond his data (x50)
2) A uniform decay of a process known to not change in a uniform manner
3) An outoffavor model for the source of the earth's magnetic field
4) There is no force that "drives" the field (i.e., no energy input)
5) The nondipole component of the field can be ignored
6) A better straightline fit to the data can be ignored
If Mr. Kiledal is curious about these topics in more detail, he is
encouraged to read (Dalrymple, 1983) or (Dalrymple, 1986, pp. 5457).
We get this topic regularly in talk.origins as an alleged "proof" of a
young earth and I'm sure most people here are tired of hearing about
the small details.
References:
Dalrymple, G. Brent, 1983, "Can the Earth be Dated from Decay of Its
Magnetic Field?", Journal of Geological Education, 1983, Vol. 31,
pp. 124133.
Dalrymple, G. Brent, 1986, "USGS OpenFile Report 86110: Radiometric
Dating, Geologic Time, and the Age of the Earth: A Reply to ``Scientific
Creationism''", U.S. Geological Survey, 76 pp.
The latter paper (Dalrymple, 1986) is an excellent introduction to
radiometric dating and creationist criticisms thereof. It is available
from the Government Printing Office for $14, but I have the author's
permission to distribute it and will send a copy to anyone who is
willing to cover postage (~$2.20 for anywhere in the United States).
This topic is also covered well in Strahler's _Science and Earth
History_.
There is also a Canadian anticreationist publication which graphs
Barnes's data and his extrapolation. It is quite an eyeopener. Ask
me via Email if you want an address to order the issue.
=============================================================================
(II) CAN THE RECENT HISTORY OF THE EARTH'S MAGNETIC FIELD BE MEASURED?
It's trivial to shoot Barnes's propositions full of holes, but it
is even better to try to test them by measuring the strength of the
earth's magnetic field back beyond Barnes's limited data. This can
be done by measuring the remnant magnetism in lava flows and
archaeological objects (e.g., clay pots). If Barnes were correct,
then the data would confirm his exponential extrapolation. However,
the data refutes Barnes.
The diagram I've seen appears originally in (Chapman, 1980) and is
reproduced in (Dalrymple, 1983) and (Dalrymple, 1986, Figure 15).
It shows a decreasing trend over the last 2500 years (or so),
preceeded by an increasing (on average) trend that covers 2000 years.
The data indicates that the strength of the magnetic field from about
8000 years ago to about 4000 years ago was slightly less than its
present strength. (Barnes's "model" predicts that the strength of
the field would have been approximately 20 to 50 times its present
value, during that same interval.)
There is no support from the measurement of remnant magnetism for a
continuous field decay, linear or exponential. This is not too
surprising, as there is ample evidence that the entire field has
reversed itself several times through history  meaning that any
unidirectional extrapolation would be senseless.
References:
Champion, D. E., "Holocene geomagnetic secular variation in the
earth's magnetic field in the western United States: Implications for
the global geomagnetic field", Ph.D. Thesis, California Institute
of Technology, 1980.
Dalrymple, G. Brent, 1983. See Section (I).
Dalrymple, G. Brent, 1986. See Section (I).
=============================================================================
> Lifeforms who died about 8000 years ago then may have had very little
> C14 in them. As a result, they would appear to be much older than they
> really are if you hang on to Benjamin's 2nd assumption.
(III) IS THE [14]C CONTENT OF THE ATMOSPHERE ASSUMED CONSTANT FOR
"CARBON DATING"?
Youngearth creationists, who know full well that carbon dating works
in general, have to compress 40,000yearold dates into their 4,000year
postflood history. In doing so, they propose the same thing which
Mr. Kiledal proposes here (though Kiledal appears to allow twice the
creationists' timescale).
Neither Mr. Benjamin nor any lab performing carbon dating assumes a
constant level of concentration of [14]C in the atmosphere over time.
The carbon dating method is calibrated against the dendrochronological
scale (a continuous sequence of tree rings which goes back about
8,000 years). Here is how that is done:
The same equation used to calculate an "age"...
age = halflife * logbase2 (c14original / c14now)
... can also be solved for another variable and so used to calculate
[14]C level at the time of formation, when the age of the object is
known by another means ...
c14original = c14now * 2 ^ ( age / halflife )
We can carbon date the tree rings from the dendrochronological scale,
and then construct a plot of "dendrochronological age" (i.e., ring
count from present) versus carbon "date" assuming today's [14]C level.
That plot would indicate how much the [14]C level of the atmosphere
has changed over time (by indicating disagreements between the two
dating methods  dendrochronology and uncorrected [14]C "dating").
If Mr. Kiledal and the youngearth creationists were correct,
the plot would show that these [14]C "dates" are badly out of whack
with respect to the dendrochronological scale as we get back into the
past. A level of half of the present [14]C level would result in an
error of about 5500 years in the resulting "date."
This plot appears in (Dalrymple, 1986, Figure 10) and also in (Ralph
and Michaels, 1974). It shows that [14]C "dates" from 1000 AD to
500 BC generally are from 0 to 200 years "younger" than the dendro
chronological dates. Beyond that, to about 5500 BC, [14]C "dates" are
about 10% "older" than dendrochronological dates (with 5% variation in
either direction). None of the [14]C "dates" are more than 900 years
off.
[NOTE: I'm putting "scare quotes" around "dates" because
these are not actual [14]C ages. They are uncorrected for
changes in the [14]C content of the atmosphere, which is
necessary in order to COMPUTE those changes in [14]C level
with time. Once the computation is done and a correction
is arrived at, we can compute actual [14]C ages of things
whose age is not known by any other means.]
Derived from such a table is a graph of the "correction" to be applied
to a [14]C date. This is the calibration which takes into account the
varying level of [14]C in the atmosphere over time. A sample diagram
of these corrections can be found in (Faure, 1986, p. 391). When a
[14]C age is corrected in this manner, as is standard procedure, the
resulting age is not dependent on the assumption of a constant [14]C
level of the atmosphere.
Thus, Kiledal's proposal fails on two counts. First, there is no
assumption of a constant level of [14]C in the atmosphere in carbon
dating. Second, there is positive evidence that the [14]C level of
the atmosphere has been within 10% or so of its present value for the
past 8,000 years. (I understand that other calibrations, e.g. ocean
sediments, have been used to calculate the [14]C content of the
atmosphere back to about 40,000 years BP. But I do not have a reference
handy for that.)
References:
Dalrymple, 1986, See section (I)
Faure, G., 1986, _Principles of Isotope Geology_ Second Edition, John
Wiley & Sons.
Ralph, E. K., and H. N. Michaels, "Twentyfive years of Radiocarbon
dating", _Amer. Sci._, Vol. 62, pp. 553560.
=============================================================================
> Erik Kiledal
It is interesting to note that Mr. Kiledal reappeared, removing the
"noncreationist" label from his signature in the same article where
he advances a standard (bogus) youngearth creationist argument. Is
it a coincidence or is it that a facade is being dropped?
I strongly recommend Mr. Kiledal get a copy of the Dalrymple paper
and read it so that he will get a basic understanding of radiometric
dating. He jumped on a couple of people pretty hard in regard to
mammoths, but he's as much in the dark on this topic as anyone else
was on that other one. Are you up to the challenge, Erik?
EMail Fredric L. Rice / The Skeptic Tank
