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The plausible continuity from minerals to modern enzymes leads us to characterize the emergence of metabolism as an 'enfolding' of geochemical mechanisms in organic control systems, as much as the creation of a genuinely novel system.

The fact that carbon fixation is not only simple, but that it is simple in this way - with explicit links to minerals and the periodic table - leads us to propose that the same set of constraints can have been both causes of limited evolutionary innovation in the world of moderns cells, and yet common to the cellular world and back through pre-cellular life and protometabolism to prebiotic geochemistry.

The central role and high concentration of phosphorus in biochemistry is disproportionate to its availability in most geochemical settings on Earth today. There are good reasons that no other chemical group may be able to do what phosphorus does in biochemistry, but its inevitability alone does not address the problem of either obtaining it or using it as a vehicle of disequilibrium.

The role of heredity and selection in population processes is mathematically identical to the role of Bayesian updating in certain problems of optimal inference. It is so general that one level it describes everything, and for the same reason it inherently describes nothing in particular.

An important and interesting question, which we do not know how to answer, is whether the geological activity on Earth today, and the subsystem of the biosphere supported by means of it, continues to be essential to maintaining the biosphere as whole, including its phototrophic constituencies.

Almost all hydrogen outside the litosphere today is bound in water. To escape it must first be unbound by UV photolysis, which occurs in the stratosphere. The existence of a liquid reservoir of water in the ocean, and of condensation at the top of the troposhere keeps the stratosphere dry and limits the delivery of hydrogen to the exobase. Condensation in turn depends on the Earth's being sufficiently cool.

The actual structure of the life we know is deeply and pervasively anchored in the particularities of the periodic table. If one wishes to propose an abstraction of 'life' away from its chemical substrate, one should first consider seriously the depth of this embedding, and should ask, if the chemical particulars were removed, how much of the structure we think of as living would remain to be abstracted.

Constraints on ecological function are more central to the earliest stages of biogenesis than most properties of organisms, and the ecosystem is the proper level of aggregation to recognize as the bridge from geochemistry to life.

A typological classification based on the directions of electron flow in metabolism reveals the greatest simplicity in the grouping of organisms. The same classification criteria apply at the ecosystem level, where they reveal greater universality than they do at the level of species.

Just as functions within computer science, ecosystems must become first-class citizens in biology.