Quote:
Originally Posted by kennyc
Link is working now. Doesn't seem very relevant as it is related to the Age of the Earth based on temp differential. (but somewhat associated)
|
It is relevant
because the Earth is still far too hot to be billions of years old if there was no other source of heat.
See
this page which quotes an article from Scientific American v261 p90 August, 1989, which says, in part:
To derive the earth's age, Thomson calculated how long the earth
required to cool from its primordial to its present state. He conjectured
that the gravitational contraction that formed the earth had generated all
of the earth's heat (except for a small contribution from the sun). Then he
investigated how well the earth conducts heat and how much heat is
necessary for it to melt or to raise its temperature by a certain amount.
He knew that the earth had cooled steadily as energy radiated into the cold
vacuum of space, according to the second law of thermodynamics. Using
Jean-Baptiste-Joseph Fourier's theory of heat conduction, he predicted how
the earth's temperature distribution might have evolved [see "The Fourier
Transform," by Ronalf N. Bracewell; SCIENTIFIC AMERICAN, June]. He
corroborated his calculations by accounting for heat from the sun and the
effects of tidal friction. In time he refined his estimate of geological
history to from 20 to 40 million years.
Thomson's work distressed geologists, who were comfortable with the
idea of unlimited time. They resented this audacious physicist who meddled
in their field, but they could not fashion a counterargument, and they
produced few papers on geochronology.
Thomson's calculation seemed unassailable on the grounds of logic and
physics. His conclusion eventually proved to be inaccurate by a wide
margin. Still, Thrason had instigated a conceptual coup d'etal: qualitative
geochronology was overthrown in favor of quantitative methods. Until the
end of the century, Thomson's estimates were the standards against which
all others were compared.
There was nothing wrong with Kelvin's calculations-- an Earth at this temperature could only be a very few tens of millions of years old if there was no radioactivity (which he couldn't account for because it hadn't been discoverd.) Inversely, without radioactivity, an Earth that IS this age would be far, far colder than it is now.
Note this quote from Chris Peterson, an astronomer at CalTech, responding to some jerk named "Darren Garrison" on a mailing list:
"Nevertheless, the Earth would have long ago cooled to a solid interior were
it not for the continued production of interior heat from radioactive decay.
There is more to it than simply the radiative loss of the heat of formation.
This is also a factor in the cooling rate of smaller bodies that are
responsible for iron meteorites. That is, even small bodies cooled slower
than might otherwise be expected, because of active internal heating from
radioactive decay (something that I think was touched upon earlier)."
(From the
metlist archives, which are
publicly available.)