Hugh Ross, The origin of Life page 42
Given the number of possible scenarios under consideration by the scientific community and the complex relationships among these models, developing a consistent set of predictions from them hardly seems possible. The challenge is heightened by the fact that predictions are often closely tied to a model’s details. Nevertheless, from the shared features of these evolutionary theories come nine general predictions:
1. Chemical pathways produced life’s building blocks. For natural processes to explain life’s beginning, investigations must identify plausible chemical routes that could generate life’s buildingblock molecules (amino acids, purines, pyrimidines, sugars, fatty acids, and so on).
2. Chemical pathways yielded complex biomolecules. Once life’s building-block molecules formed, plausible chemical routes and processes must have existed for them to condense into the molecular entities that ultimately led to the complex biomolecules central to the cell’s structural and functional components. These biomolecules include DNA, RNA, proteins, and membrane and all cell-wall components.
3. The chemical pathways that yielded life’s building blocks and complex molecular constituents operated in early Earth’s conditions. Not only must origin-of-life models identify plausible chemical routes that yielded life’s molecules, but these routes also must have operated under early Earth’s conditions and generated sufficient material to allow life to evolve.
4. Sufficiently placid chemical and physical conditions existed on early Earth for long periods of time. This prediction is a necessary corollary to the previous one. While the production of prebiotic compounds required high-energy conditions, these conditions could not persist for long without destroying the very molecules they formed. Fragile complex biomolecules like DNA, RNA, and proteins are particularly susceptible to breakdown by water and to breakage by mechanical, shear stresses.
5. Geochemical evidence for a prebiotic soup exists in Earth’s oldest rocks. Regardless of the source of prebiotic compounds, if a prebiotic soup existed on early Earth as a necessary preamble to life’s origin, then evidence for it should be discovered in the oldest layers of Earth’s geological column. (Of course, this prediction need not be a part of models in which life originates beyond Earth.)
6. Life appeared gradually on Earth over a long period of time. The transition from the prebiotic starting materials thought to have been present on early Earth, through a prebiotic soup to the first cellular entities, would require many chemical steps. Some of these steps proceed slowly, while others seem highly unlikely. Given these facts, life’s emergence should have required a long time to unfurl once Earth’s conditions could feasibly support life.
7. The origin of life occurred only once on Earth. This prediction stands as a corollary to the previous one, especially considering the number of steps required to generate first life from nonliving chemical entities and the low probability of some of the steps. In other words, it was such a lengthy, unlikely process that it could, at most, have happened just once.
8. Earth’s first life was simple. Given the arduous process required to generate the first lifeforms, it follows that life as it first appeared on Earth must have been simple, both in terms of its chemical makeup and its morphology, or form.
9. Life in its most minimal form is demonstrably simple. Life’s minimal complexity describes the fewest number of different biomolecules that must have simultaneously co-occurred for life to originate. For a realistic probability of emergence through natural processes, life’s most minimal form must have been relatively simple.