On Sun, 12 Sep 2004 18:23:23 +0000 (UTC), Tim Tyler 
wrote:

>Brett Aubrey  wrote or quoted:
>
>> I've always assumed that a fresh water primal soup might
>> allow presumably delicate first life more readily than salt
>> water.  This assumption is mainly due to the purity of the
>> source...  that is, since water is a necessity for life, the
>> impurity of salt (, etc.?) might be just one more issue to
>> hamper beginning life.  Can anyone out there comment
>> (refute/confirm) that this makes some sense?
>> (Or is  there no real way of even guessing at this?)
>
>Quite a few OOL scenarios put the OOL on the ocean floor.
>
>Others invoke evaporative tidal pools.
>
>I'd say that the odds were that the water was pretty salty.

Fresh water is an enormously difficult environment for cells to live
in.  Sea water is easy!

The problem is maintaining osmotic balance across the cell membrane.
Cells must contain a certain internal concentration of ions and
organic chemicals to sustain life.  Fresh water is extremely dilute --
for osmotic purposes it is essentially equivalent to distilled water.
As a result, cells in fresh water are constantly taking in water
osmotically.  Without a rigid cell wall to support the resulting
pressure (turgor pressure), the cell will burst.  Protistan animal
cells (protozoans) without cell walls have elaborate systems like
contractile vacuoles to bail out the water.

Maintaining an internal ion composition sufficiently concentrated to
balance the concentration of salt water and thus remain in water
balance is trivial.  It is simple enough to maintain some membrane
pumps so the specific ion concentrations intracellularly can differ
from the external environment without disturbing the osmotic balance.

Another problem with fresh water is the extreme variability of
chemical composition of the environment with the effect of rainwater
or tidal wash.  The oceans are extremely stable environments.

Go with salt  water.
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