I outline a general thermodynamic condition for the earliest steps in the origin of life based on fluctuation theorems developed in the last two decades. I argue that the exponentially developing loop of asymmetric autocatalysis and thermodynamic tail-wind condition (TTC) in the prebiotic clutter was a key to a particular trajectory of decluttering via a sequence of early symmetry breaking events. Such decluttering was bound to result, most prominently, in homochiral amino acids and homochiral sugars composing nucleotides as the TTC exponentially favoured asymmetric autocatalytic processes over catalytic and symmetric autocatalytic processes in the clutter. I describe the loop's structure, including its chemical and physical properties, and explain that the TTC/asymmetric autocatalysis loop intersected with multiple chemical, geological and climatological feedback loops, thus providing conditions for the propagation of living systems as we know them.

The emergence and spread of chirality on the early Earth is considered by studying a set of reaction-diffusion equations based on a polymerization model. It is found that effective mixing of the early oceans is necessary to reach the present homochiral state. The possibility of introducing mass extinctions and modifying the emergence rate of life are discussed.

The astrobiological relevance of carbonaceous chondrites is reviewed. It is argued that the primitive meteorites called carbonaceous chondrites provide a unique source of information about the materials and conditions in the Solar System during the earliest phases of its history, and its subsequent evolution. Presolar dust grains extracted from the carbonaceous chondrites provide direct information on the previous generations of stars that provided the materials present for planet formation. The organic material found in carbonaceous chondrites consist of amino acids, carboxylic acids and sugar derivatives. Part of the amino acids found show L-enantiomeric excesses, which indicates that homochirality on Earth could be a direct result of input from meteoritic material to the early Earth.

Homochirality is an essential feature of biology, but how it developed in early life remains unclear. Our aim in this paper is to add to the discussion by taking a somewhat arbitrary but definite sequence of events and examining carefully the chirality at each stage. Our scenario for the development of life starts with the prebiotic, continues through a pre-RNA stage to the RNA world. This leads to the development of proteins and then to the incorporation of DNA in RNA–DNA–protein biochemistry.

We argue that homochirality probably did not develop prebiotically. We see the likely chiral bifurcation point to be during the development of RNA from an achiral pre-RNA. Surprisingly, we find the driving force for this to be enantiomeric cross-inhibition in which the addition of a ‘wrong-handed’ enantiomer to a growing polymer brings the polymerization to a halt. This, it is often argued, is a serious impediment to the development of chiral purity. We suggest that the sign of handedness at this stage was probably determined by chance. We then point out that homochiral RNA was unlikely by itself to lead to homochiral proteins. We identify the additional nonlinear feature required for bifurcation to be the rapid increase in enzymic power available when the amino acids in proteins approach single handedness and structural features such as α-helices and β-sheets become viable. If this is correct, then the handedness of the protein sector is indeed linked to that of RNA. However, the relative sign of the two handednesses will have depended on the precise stereo-sensitive interaction between the RNA and protein systems. We suggest that the most plausible scenario is via the recently discovered RNA binding sites for amino acids, which are both stereo-selective and have contact with the developing genetic code. The detailed steps that determine the handedness are not yet clear and may be specific to the precise development path.

It follows that if biochemistry similar to that on Earth developed extraterrestrially, we would surely have homochirality but at this stage we cannot be sure about the handedness of either the nucleic acid or the protein components.

Models for segregation of racemic mixtures of chiral amphiphiles and lipophiles in aqueous solutions show that the amphiphiles with active isomerization kinetics can perform a spontaneous symmetry break during the segregation and self-assemble to homochiral matter. Based on physico-chemical facts, it is argued that D-glyceraldehyde, which was synthesized from the volatiles at the hydrothermal reactors at the origin of life, could be the origin of homochirality in biological systems.

Reaction-diffusion equations based on a polymerization model are solved to simulate the spreading of hypothetic left and right-handed life forms on the Earth's surface. The equations exhibit front-like behavior as is familiar from the theory of the spreading of epidemics. It is shown that the relevant time scale for achieving global homochirality is not, however, the time scale of front propagation, but the much longer global diffusion time. The process can be sped up by turbulence and large scale flows. It is speculated that, if the deep layers of the early ocean were sufficiently quiescent, there may have been the possibility of competing early life forms with opposite handedness.