Subject:
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Re: Geology from Outer Space
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Newsgroups:
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lugnet.off-topic.debate
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Date:
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Wed, 4 Apr 2001 18:33:27 GMT
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Viewed:
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534 times
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In lugnet.off-topic.debate, Jeremy H. Sproat writes:
> In lugnet.off-topic.debate, Bruce Schlickbernd writes:
> > > [quoting Ryan's argument of sun touching earth]
> > Basic bad science. Unwarranted extrapolation of evidence over a very brief
> > period. It's kind of like watching the tide going out, walking away, and
> > declaring the seas will dry up in a year, without any understanding of the
> > ocean's (or sun's) processes.
>
> Bruce (or anyone else, really :-),
>
> I have a question related to this, it's something I've pondered on but no
> teacher I've had could answer to my satisfaction, and it's one that I am
> honestly curious about and will welcome any answer that I can get.
>
> How does this "don't extrapolate linerally" rule not apply to long-range
> dating techniques, i.e. carbon dating, geologic dating, astrophysical
> dating, etc.?
This is a rather large subject that I could only cover here in the briefest
possible manner. In part, a number of techniques may be combined as
double-checks: Known decay rates of radiactivity - Carbon-14 is the best
known but there are a number of others; yearly produced tree rings;
alternating sediments laid out on seasonal basis (varve analysis, if I
recall correctly); relative age due to stratigraphy; triangulated
comparisons of distance versus time. Some are only good for certain time
frames, but can confirm some of the cyclic measurements and inferences are
made from there. Many times you *do* have to be wary, even using any of
these methods. We build up confidence in these techniques over a vast
amount of consistent results and an understanding when they may not work
(potassium-argon dating can reset itself if the test subject gets too hot,
for example, and you are dating from the reheat rather than actual formation).
To actually answer your question is we futz about with things until we have
reasonable confidence they work. :-)
> What kind of baseline is used in the measuring systems we use
> to get the earth's age, and what corroborating evidence is used to back it
> up? It seems to me that it would be extremely difficult to measure any age
> past a few thousand years when we've only been measuring these things for a
> couple hundred. There could be a (time-? distance-?) curve involved that we
> haven't even seen yet.
Here's an example of establishing part of a time frame through polar
reversal and sea-floor spreading. In the middle of the Atlantic Ocean (just
using it as an example) there is the mid-Atlantic ridge. This runs down the
length of the Atlantic Ocean, and is an area where magma wells up and slowly
adds to the ocean floor on either side. The Atlantic Ocean has been getting
wider at a very small but even rate as long as we have been observing it,
which isn't very long. If the rate is even, we can calculate how long ago
the continents were actually connected (early explorers noted very quickly
how the coastlines of South America and Africa seemed to fit each other like
puzzle pieces).
Why do we think the sea-floor spreading has been consistent over the
millenia? The second part of this is polar reversal. Every now and then (I
think it's 10,000 years, but I honestly forget) the poles reverse. North
becomes south and vica versa. Scientists have been making computer models
as to why this happens (magma corkscrewing near the center of the earth
reversing its flow), but it's mostly conjecture. Anyway, it happens. We
know this because as the new rock forms near the ridge, the molecules align
magnetically as the rock cools. As you go out from the ridge, the alignment
of the molecules will suddenly flip-flop. Go out the same distance again
and it will change back. And again. Now, its possible that the rate of
spreading increased in direct proportion to the flips in the poles, but
there were be other indicators that the rock was forming at a rapid rate in
the past (crystalization, formations, etc.). All evidence is consistent
with the new rock forming at a fairly even rate over the entire period.
Count the distance, and you get a pretty good idea of the time involved.
My advice would be to look into it in an encyclopedia - the whole subject
exceeds my knowledge to explain it adequately.
>
> In terms of distance (and the way I understand it), the measuring stick is a
> meter long, our reach maybe a meter more, and we're guessing the distance of
> something so far away that it's beyond our capacity to focus on it. It
> seems we need a measuring stick that's both within our capacity to weild yet
> at some gargantuan scale -- and a *second* mesauring stick of a sufficiently
> different nature but otherwise identical qualities, which we can use to
> verify the results of the first one.
Yep. Boggles the mind at times.
>
> Granted, we can make some educated guesses (e.g. species in the fossil
> record don't appear and disappear in just a few years), but just how do you
> count 4 billion years? How can it be expected that the rules that we
> measure things by apply to events that happened so long ago?
Experimentaion in part, calculation in others. Is the sun 3 billion years
old or 5 billion? Studing similiar stars and their progression through age.
Calculated rate of consumption of fusionable materials. Most of these
aren't that exact, just reasonable estimates based on the evidence on hand,
and subject to change as new information and technniques are developed.
Some things we are fairly certain of, others are simply (highly) educated
guesses where we can only make a much more vague deduction.
I've barely scratched the surface and see how much I've written. Woof.
Bruce
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Message has 1 Reply:
 | | Re: Geology from Outer Space
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| (...) Oh, so it's just like computer programming! :-, (...) Got it, thanks for the example. (...) I've done this, at least with World Book (I read this thoroughly when I was youger :-) and Encarta (blech) and a couple of other brands. They just (...) (23 years ago, 4-Apr-01, to lugnet.off-topic.debate)
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Message is in Reply To:
| | Re: Geology from Outer Space
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| (...) Bruce (or anyone else, really :-), I have a question related to this, it's something I've pondered on but no teacher I've had could answer to my satisfaction, and it's one that I am honestly curious about and will welcome any answer that I can (...) (23 years ago, 4-Apr-01, to lugnet.off-topic.debate)
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