hms beagle

What is the current best theory for the formation of the first cell on
earth?

(And while we are on the subject, I find it disturbing that
scientists are saying the first DNA strands were carried to the earth
from some other location via meteor impact. Unless, that is,
scientists are saying something else. If they are, please let me
know. Neverthless, lets try to concentrate first on the cell wall
issue.)

tim tyler

IMO, the correct theory is that the first cells were the product of
natural selection.

In other words, there were early organisms which existed *without*
cell walls, and they constructed cell walls via natural selection -
probably to protect themselves from their environment and to
control their immediate environment.

Most speculation surrounding these events appears to be focussed
around the idea that the first membranes formed on mineral surfaces -
creating a protected two dimensional arena beneath them - and that
these "blisters" led to "bubbles" - and then eventually to free- living cellular organisms.

Panspermia.

The idea of the Earth originally being seeded with life from Mars
seems to be fairly widely regarded as being quite credible.

The idea of life in the solar system coming from elsewhere is
usually not regarded so favourably.
--
__________
|im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply.

graemew

Wikipedia has a good overview at
http://en.wikipedia.org/wiki/Origin_of_life. Talk.origins has more
details, including some nice diagrams, at
http://www.talkorigins.org/faqs/abioprob/abioprob.html.

-- Graeme

john wilkins

I'm glad you liked my diagrams :-)

--
John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project
University of Queensland - Blog: evolvethought.blogspot.com
"Darwin's theory has no more to do with philosophy than any other
hypothesis in natural science." Tractatus 4.1122

earle jones

*
There is an interesting essay by Dr. Harold Morowitz (Yale PhD in
Biophysics -- Prof of Biophysics at George Mason University) on the
subject of amphiphilic molecules and how their evolution had to
occur before a cell wall could exist.

Amphiphilic molecules, Morowitz tells us, are long molecules that
have the ability to bind to water on one end and to an oil (lipid)
on the other end. Until these molecules came into being, the idea
of a cell wall was impossible.

Egg yolks (and lecithin) are common souces of amphiphilic molecules.

The making of mayonnaise is substantially the problem of mixing oil
and water -- we all know that's impossible. But blend them together
with a bit of egg yolk and they produce that delectable and
fattening product we know and love!

Read "Mayonnaise and the Origin of Life" by Harold Morowitz -- an
entertaining essay written at a lay level.

(Even I could understand it!)

earle
*

perplexed in peoria

Thx for the reference. I agree with Morowitz that amphiphilic molecules
and membranes probably arose before cell walls. But there is an
interesting theory by Michael Russell et al. which disputes this. See:

http://www.gla.ac.uk/Project/originoflife/index.htm

The idea is that you have a semi-permeable mineral shell around the
organic stuff. I would call this a cell wall rather than a membrane,
since it is more-or-less rigid. Interesting idea, but I think you
still need a fissionable membrane for reproduction.

tim tyler

My favourite quote from there:

``What does Life do?

It responds electrochemically to geochemical and photochemical tensions
on Earth by attempting to resolve them, remaking itself in the process
that it might create a greater overall disorder. Or in the words of
Simon Black (2000) -"energy uses an organism as a mechanism for self-dissipation."''

There's also the old idea that early organisms took shelter inside
porus rocks long before they developed cell walls.

Many rocks are porus - and contain small hollow regions - where volcanic
gasses were, or in the form of impurities that have subsequently been
washed away.

The idea is that these played the roles of providing a stable controlled
environment for organsms - and helped keep their components together -
while still allowing the components to exit from their shelter and infect
other regions.

Sandstone is the rock most frequently mentioned in this context - e.g.
see "Seven Clues to the Origin of Life" - pages 100-102.
--
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