Susan:
>>I was talking about cosmology and the scientific principle of collecting
>>evidence. What the heck are *you* talking about?
Cliff Lundberg:
>I'm talking about your assertion that in Darwin's time the planet was
>thought to be mere millions of years old, and that this was a problem for
>his theory, which was solved by more modern geological dating, which
>allowed much more time for evolution to take place. If this was a problem,
>as you assert, it has been revived by recent findings about the pace of
>evolution in the Cambrian. The time frame for the emergence of the major
>phyla is down to 5 million years, and those capable of extrapolating trends
>won't be amazed to learn that the window is even smaller.
Where are you getting your date for 5 million? The Cambrian lasted about 70
million years. There are (I think 3) phyla that are thought to pre-exist
the Cambrian and at least one that arose afterward. This is from the
Encyclopedia Britanica:
"At least 11
extant animal phyla (Annelida, Arthropoda, Brachiopoda, Chordata,
Ctenophora, Echinodermata, Hemichordata, Mollusca, Onychophora, Porifera,
and Priapulida), including most of those with a fossil record, first appear
in Cambrian rocks. Most of these rapidly diversified as they seemingly
adapted to numerous unfilled ecological niches. Another five phyla
(Nemertea, Phoronida, Platyhelminthes, Pogonophora, and Sipuncula) are
questionably known from Cambrian fossils. The only extant animal phylum with
a good fossil record that is not known from Cambrian rocks is the Bryozoa,
which first appears in rocks of Early Ordovician age."
>>The Cambrian again?
>
>'The Cambrian, never again' would be more apt. Evolutionary events
>occurred then that were qualitatively different from what happened before
>or since.
I disagree with "qualitatively." Certainly more rapid than usual.
>>Do you
>>realize that 5 million years is *500 TIMES* the length of time our own
>>species has been on the earth? It's not exactly a snap of the fingers.
>
>550 million is years is a long time too, a long time with no new
>phyla appearing. What's the explanation?
a tree does not put out new branches from its trunk? There are not huge
wide-open nitches? Oxygen use will never be new again?
>>Also you seem to be ignoring the fact that there are plenty of
>>pre-Cambrian fossils.
>
>Yep, they just don't seem that complex, compared to the Cambrian
>fauna.
to you. They were quite complex.
>>You also seem to think that the rapid origin of *phyla* is
>>significant. Why?
>
>Rapid origin of whole complex new forms is antithetical to the
>evolutionary theory I was taught. When the facts conflict with the
>theory, that's significant.
It has been demonstrated repeatedly that evolution can proceed very rapidly
at times. There is still a great deal to learn about the Cambrian, but it
is not a total mystery. For example that is also the time when the
atmosphere became oxygenated. That *might* have something to do with it.
That's an event that will only happen once (we hope!) and therefore perhaps
the life that developed then will only develop that way once. Even so, 70
million years is a good long time for evolution to take place. The Cambrian
"explosion" is only comparatively rapid.
The short timespan that Darwin had to work with was only about 5-10 million
years. *Way* too short for even a Cambrian-style explosion. Also Darwin
wasn't just concerned with the origin of the phyla, but of all the species
we see today. Even given a starting point in the Cambrian for most phyla
that's still 540 million years for the rest of life to develop.
>>So what? What about all the classes, orders and families
>>that have evolved since that time?
>
>Incremental Darwinian change. Why no new phyla?
the conditions available then will never be available again.
>>What about the fact that almost none of the animals and plants
>>living then still exist?
>
>Their descendants have been modified through Darwinian
>evolution. No problem. The problem is the absence of major
>new developments, in contrast to the rapidity of new developments
>in the early Cambrian.
>I don't see what fun there is in indignantly arguing for old evolutionary
>dogma, and ignoring the anomalies that make the subject interesting.
The Cambrian is an anomoly, yet it's not. There have been other
"explosions" and die-offs since that time. The Cambrian certainly is
interesting, but I'm not sure what you are getting at. It's obviously not
the creation event, there were animals alive before it. Also a great many
new phyla that evolved at that time which have since died out. Our
phylum--cordata--includes mammals, birds, fish, and reptiles. What's
remarkable about the original emergence of cordata?
And I still don't know what you are getting at. Say what you are saying.
Susan
----------
For if there is a sin against life, it consists not so much in despairing
of life as in hoping for another and in eluding the implacable grandeur of
this one.
--Albert Camus
http://www.telepath.com/susanb/