a)  Formation of building blocks (amino acids, nucleotides) from early earth atmosphere
 
 

1).  Best estimate of early earth atmosphere not consistent with synthesis of amino acids or nucleotides (oxidizing vs reducing)

 
 used in experiments:
 

 H₂O, NH₃, CH₄, H₂   (formation of amino acids is favored)

 actual (best estimate from atmospheric physics, geology):
 

 H₂O, N₂, CO₂, (O₂?)    (formation of amino acids not favored,
                                         requires energy, O₂ destroys organics)

 

2)  Without oxygen, no ozone so UV destroys organics
 

(In Miller-type expt - selective use of certain wavelengths, quick removal)

 
 

3)  Building blocks of RNA, DNA cannot be synthesized under prebiotic conditions
 

"The evidence that is currently available does not support the availability of ribose on the prebiotic earth, except perhaps for brief periods of time, in low concentration as part of a complex mixture, and under conditions unsuitable for nucleotide synthesis."

    R. Shapiro, Prebiotic Ribose Synthesis,presented at a meeting of the
    International Society for the Study of the Origin of Life
 
 

"To avoid the need for ribose, some authors have preferred to invoke an RNA-like polymer, with a simpler or more accessible backbone, at the start of life. ... These suggestions still presume that the bases adenine, cytosine, guanine, and uracil were readily available on early Earth.  I have argued that this presumption is not supported by the existing knowledge of the basic chemistry of these substances."

 R. Shapiro, Proc. Nat. Acad. Sci. 96, 4396, 1999
 
 
 
 

b)  Polymerization - Proteins, DNA, RNA, Lipid membranes
 

 
 1) concentration of building blocks
 
 

 2) polymerization of amino acids requires removal of water
 
 

 3) energy sources break down as well as polymerize

(equilibrium favors smaller molecules)

 

 4) competing cross reactions (thousands)
 
 
 

 5) chemical chirality

         (proteins - only left handed amino acids,   DNA/RNA - only right handed nucleotides)
 
 

 6) origin of information

         (not just any sequence, 3-D structure of proteins essential to function)

 
"Our task is to find an algorithm, a natural law that leads to the origin of information."
      Manfred Eigen, Steps towards Life:  A perspective on Evolution, 1992, pg 12.
 

"the problem of the origin of life is clearly basically equivalent to the problem of the origin of biological information."
       Bernd-Olaf Kuppers,  Information and the Origin of Life, 1990, pg 170-172
 

"Theories of prebiotic natural selection need information, which implies that they have to presuppose what is to be explained in the first place."
       Christian de Duve
 

"Viewed in this way, the problem of the origin of life reduces to one of understanding how encoded software emerged spontaneously from hardware."
        Paul Davies, The Fifth Miracle, 1999, p 115.
 
 

 7) irreducible complexity of existing DNA/protein systems

enzymes needed for protein synthesis, DNA needed to specify sequence of amino acids in enzymes

(How could one part function alone?)
 

 "to build a single protein or DNA molecule in a cell, about 60 specific proteins acting as enzymes are needed."

         Davis and Kenyon, Of Pandas and People, pg 53.

 
 

c)  Assembly into protocells
 

  molecular machines and irreducible complexity  (see next section)