Re: How does life come from non-life?

This is the million-dollar question, but no one has the answer yet!  
Scientists are working on several different scenarios to determine how life 
came about using the molecules that existed on the early Earth.  Three 
basic ideas have been suggested: the DNA world, the protein world, and the 
RNA world.

The DNA world is the proposed stage in the evolution of life that says DNA 
strands were created first and then lead to the formation of life.  Given 
the compexity of DNA and the unlikelihood that complexity came before 
simplicity, recent findings have forced this theory to fall out of favor.

The protein world is the proposed stage whereby life started when chains of 
amino acids were formed.  Since amino acids are the "building blocks of 
life", this idea was highly regarded for many years. 

However, new discoveries of the characteristics of RNA have lead to the 
acceptance (for the most part) of the RNA world.  This is a proposed stage 
early in the evolution of life in which RNA acted as both genetic material 
and enzyme.  This means that RNA can store genetic information as well as 
act as a catalytic molecule and suggests that this important biopolymer may 
have evolved on Earth well before DNA and protein.  Experiments have 
revealed that certain type of naturally occurring RNA (ribozymes) could act 
as their own enzymes, snipping themselves into two and splicing themselves 
back together again.

But what started the activity of the molecules in the first place?  Several 
groups are using minerals as catalysts in order to activate biomolecules 
and form long chains of amino acids (oligomers).  It's generally thought 
that an oligomer of 50 units (50-mer) is the minimum length required for 
life.  To that end, Jim Ferris' group at RPI (1) is using montmorillonite 
clay to catalyze the formation of oligomers.  After 14 days of successive 
feeding with the monomer ImpA, chains up to 55-mer long have been created. 
 The chain elongation takes place with both D- and L- monomers, which is 
great because both D- and L- enatiomers of mononucleotides required for RNA 
synthesis were probably present on the primitive Earth.

A recent paper by Hazen et al. (2) suggests that the emergence of 
biochemical chirality was a key step in the origin of life, and they have 
shown that the terraced surfaces of calcite crystals act as points along 
which homochiral polypeptides can form.  Thus, geochemical mechanisms seem 
to be required for the emergence of biomolecules.

Saghatelian et al. (3) used peptides to show that homochiral molecules 
readily self-replicate and so can rise to dominance in an initially 
heterochiral mixture.  This suggests that self-replicating peptides could 
have played a crucial rold in the emergence of life.  Since peptides are 
the smaller "cousins" of proteins, this gives support to the protein world 
hypothesis.

It's very difficult to "make life from non-life" because we don't really 
know what the conditions of the primitive Earth were truly like.  We have 
some idea, of course, but to get the right mixture of molecules, water, and 
energy together in the same place at the same time under the right 
conditions is quite challenging.  The early Urey/Miller experiment (whereby 
they formed amino acids from a mixture of molecules they thought were 
present in the early atmosphere) got us started, but we still have a long 
way to go.  We're working on it, though!

We can't bring people back to life because either (1) their cells are too 
old and worn out (old age or organ failure); (2) their cells are damaged 
beyond repair (cancer); (3) their cells lack the necessary oxygen for 
humans to live; or (4) any number of other scenarios.  This questions is 
probably better answered by a physician or coroner!



References:

(1) http://www.origins.rpi.edu   
The New York Center for Studies on the 
Origin of Life. Rensselaer Polytechnic Institute. Troy, NY.

(2) Selective adsorption of L- and D- amino acids on calcite: Implications 
for biochemical homochirality.  PNAS. May 8, 2001. 5487-5490.

(3)  A chiroselective peptide replicator.  Nature. 2001. vol. 409. 797-801.