> I do not deny that researchers in the past tried to push the reducing
> atmosphere out to several billion years, but as I posted a couple of
months
> ago, the best evidence indicates that it lasted only 500 to 800 million
> years, roughly between 4.5 and 4 billion years ago. As such, this latest
> research comes as no surprise to me, and actually helps to support the
data
> I cited.
DJT: As was explored last year, this "best evidence" is not based on
rocks, as we do not have them from this "window" of earth history.
KLOB: Since you admit that these rocks do not exist, it is rather
disingenuous to imply that only these would provide the best evidence.
However, we do have rocks from that period; they are called meteorites, and
they establish that planetesimals from that time would have had the right
composition to form a secondary reducing atmosphere when they were
sufficiently heated.
DJT: It is based on the adoption of a certain theory of planetary
formation....
KLOB: Which is about as well verified as it can be without direct sampling
of asteroids or comets, or watching the process in other solar systems (both
of which we should be able to do sometime in the next century, probably
earlier than later).
DJT: ...by analogy with the Jovian planets....
KLOB: Actually, Mason made no such inference. What he said was that the
primary atmosphere that would have been similar to Jovian atmospheres was
blown away by the solar wind; the reducing atmosphere that was present prior
to 4 billion years ago was a secondary atmosphere produced by outgassing
from the mantle.
DJT: ...and by various other inferences based on observed isotopic data.
KLOB: Mason made only one inference based on isotopic data, and that was
when he stated that the outgassing stopped sometime shortly after 4 billion
years ago. Which is supported by paleosol data and the data you described
at the beginning of this thread.
DJT: (I've just reread Brian
Harper's post to you on 23 November which reviews some of these
points.)
KLOB: Yes, well, I never responded to that post because it was simply a
rehash of what he had posted before, which I had already dealt with.
Brian's sources do not support his claims, mainly because they do not
discuss the period in question, except by implication. The data they
discuss applies to the time after 4 billion years ago, not before. Besides,
his sources are from the Eighties and early-Nineties, and so are at least
out of date, if not obsolete. And he ignored more recent evidence that I
cited which contradicted his own sources. Some of that new information even
came from one of his own source authors, indicating that these people may be
changing their minds in light of new information.
KLOB: Even so, my dispute with Brian is over whether a reducing atmosphere
had a significant impact on abiogenesis, not over the validity of
abiogenesis itself. And the mechanism he supports would actually be far
less vulnerable to degradation and meteoritic bombardment than the reducing
atmosphere mechanism would be.
> As for the implied need for "unlimited time" I would remind everyone that
> 800 million years covers virtually the entirety of metazoan evolution,
from
> the simplest hypothetical organisms through the Cambrian explosion on up
to
> modern times. That is a heck of alot of evolution for so short a time.
DJT: And if you consider that most of it was stasis, this is an even more
remarkable situation!
KLOB: That statement implies that evolution for all species throughout the
entire world occasionally just stopped. That's not what happened. Once a
new species evolved evolution made little changes in it sometimes for
millions of years, until the habitat changed, at which point the species
evolved again, went extinct, or produced a daughter species that fit the
changes. However, this process went on for each species individually. As
such, while at any time in the past you had species that exhibited stasis,
they were others that were rapidly evolving. Evolution as a whole was
continuous over this entire time, even if the individual evolutionary
development of certain species was not.
> Considering the ease with which biomolecules, including catalytic proteins
> and RNA, plus vesicles with lipid bilayers, can form, I don't consider 500
> million years to be any serious limitation to abiogenesis.
DJT: "Ease" is not the word I would use.
KLOB: I know, but that doesn't mean it's not correct.
DJT: They can form under certain specific conditions....
KLOB: And those conditions are relatively easy to reproduce and would have
been present on the early earth.
DJT: ...and they are also very quickly destroyed.
KLOB: Not that quickly, but all you would need is for synthesis to be
faster than degradation (which it almost certainly was at certain times and
in certain places), to sequester the newly formed biomolecules and to
protect them (mechanisms for both of which are well known and were also
probably present on the early earth).
DJT: However, the main point I would wish to make is that the challenge
for abiogenisis advocates is to form a replicating bio-structure.
Without replication, there is nothing for selection forces to act on
and whatever structure is formed is quickly degraded.
KLOB: Since self-replicating systems have not been abiotically made in the
lab yet, we cannot say whether they would have been quickly degraded,
wishful thinking aside.
DJT: This is my
understanding of why abiogenesis needs time: the hypothesis is that
the more time there is, the greater the probability of arriving at a
replicating structure.
KLOB: And 500 million years is certainly ample time to accomplish this,
based on what we know from the fossil record has been accomplish in that
time period.
DJT: This is also my answer to Pim's comment:
"Then again the question really is, is such "unlimited time" really
required ? The remaining time is still quite long."
KLOB: Ditto what I said above.
DJT: One last point: Kevin says that 500 million years is not a serious
limitation. But have you got 500 million years? For most of this time, the
Great Bombardment of the Earth is thought to have occurred and few would
wish to invoke abiogenesis in that environment. (No warm little ponds
during this time!).
KLOB: Actually, the "Great Bombardment" ended at about 4.5 billion years
ago. What bombardment continued after that was sporatic, short-lived and
often less than global in its effects. It may have even helped in some
cases, by infusing the biosphere with fresh organic material and by
providing the energy needed to accelerate certain abiogenetic processes.
DJT: (Maybe this is the
breakthrough abiogenesis is looking for: introduce extreme energy
sources from bolide impacts and up pops a self-replicating cell!
KLOB: Why are creationists always characterizing naturalistic events as
magic tricks or miracles? Is it perhaps because they cannot explain any
kind of phenomena without recourse to supernatural powers? Whatever the
reason, it makes them look ridiculous.
DJT: Perhaps Hoyle and Wickramasinghe were way out in their 'tornado
forming a plane out of scrap' story!)
KLOB: I find it amazing that two such intelligent men would use such hoary
crap. It's been refuted so many times you would think creationists would
get the idea by now that this is yet another one of those things that make
them look ridiculous. By the way, did you know that Wickramasinghe says
that anyone who doesn't believe that the earth and the universe are billions
of years old is an idiot?
Kevin L. O'Brien