David A. Juckett

The prebiotic chemistry necessary for the development of life requires a low-probability combination of steps to reach the complexity of a living cell. An unanswered question is how big the reaction space must be to favor this process, if it is driven by stochastic forces. The space must be large enough and diverse enough to provide reaction centers as well as storage reservoirs to hold chemical intermediates. Using the carbon footprint of various lifeforms on Earth and their average cell masses, the number of cells alive today in various taxa can be calculated. It is shown that as cells increase in mass and complexity, they occupy progressively smaller shares of the biosphere and exist in smaller numbers. Conversely, the basic units of life increase in number as complexity decreases. Following this trajectory to the starting atomic elements of life yields a count of the CHNOPS needed to enable prebiotic chemistry to begin. Estimates of the starting volume of water necessary to contain this number of elements approaches the volume of Earth’s oceans. Furthermore, assigning the cell counts of various taxa to their times of first appearance on Earth yields a linear regression that can be extrapolated back in time to a point when only CHNOPS existed. This occurs at ~9.0 Gyr before the present. The implications of these findings are discussed, with a particular focus on a world existing 9 Gyr ago, with characteristics similar to Europa, with a large, protected water environment that can store chemical intermediates over a long time and thereby support combinatoric prebiotic chemistry.

The origin of life embodies two fundamental questions: how and when did life begin? It is commonly conjectured that life began on Earth around 4 billion years ago. This requires that the complex organization of RNA, DNA, triplet codon, protein, and lipid membrane (RDTPM) architecture was easy to establish between the time the Earth cooled enough for liquid water and the time when early microorganisms appeared. These bracketing events create a narrow window of time to construct a completely operational self-replicating organic system of very high complexity. Another conjecture is that life did not begin on Earth but was seeded from life-bearing space objects (e.g., asteroids, comets, space dust), commonly referred to as panspermia. The second conjecture implies that life formed somewhere else and was part of the solar nebula, originating from an earlier generation star where there was more time available for the development of life. In this paper, the goal is to provide a hypothetical perspective related to the timing for the origin of pre-biotic chemistry and life itself. Using a form of complexity growth, biological features spanning from the present day back to early life on Earth were examined for trends across time. Genome sizes, gene number, protein–protein binding sites, energy for cell construction, mass of individual cells, the rate of cell mass growth, and a molecular complexity measure all yield highly significant regressions of linearly increasing complexity when plotted over the last 4 Gyr (billion years). When extrapolated back in time, intersections with simple complexities associated with each variable yield a mean value of 8.6 Gyr before the present time. This era coincides with the peak of star and planet formation in the universe. This speculative analysis is consistent with the second conjecture for the origin of life. The major assumptions of such an analysis are presented and discussed.

Epigenetic transgenerational mechanisms underpin the imprinting of gamete origin during reproduction in mammals but are also hypothesized to transmit environmental exposures from parents to progeny in many life forms, which could have important consequences in population dynamics. Transgenerational hypotheses embody epigenetic alterations occurring in gametes, embryonic somatic cells, and embryonic primordial germ cells because most of the epigenome is erased and reconstituted during development. Four scenarios are described in this paper encompassing somatic and germline effects where each of these is either non-propagating or propagating in time. The non-propagating effects could result from environmental impulses such as toxicants, weather, epidemics, forest fires, etc. The propagating effects could result from continuous signals such as climate variations, food web abundances, population densities, predator numbers, etc. Focusing on the propagating mode, a population growth model is constructed incorporating the intrinsic delays associated with somatic or germline effects. Each exhibit oscillatory behavior over a wide range of the parameter space due to the inherent negative feedback of such delays. The somatic (maternal) model oscillates with a period of ∼6 generations while the germline (grandmaternal) model oscillates with a period of ∼10 generations. These models can be entrained by oscillatory external signals providing that the signals contain harmonic components near the intrinsic oscillations of the models. The 10-generation oscillation of the germline-effects model is similar to many wildlife cycles in mammals, bird, and insects. The possibility that such a transgenerational mechanism is a component of these wildlife cycles is discussed.

Cross-generational effects (grandmother effects) associated with epigenetic imprinting, environmental exposures, and lifestyle choices are beginning to be explored by various investigators. The possibility that low-level background radiation can be a driver of such effects has been suggested previously and is explored further in this study. Age-period-cohort analysis was performed on United States (US), United Kingdom (UK), and Australian (AU) female breast cancer mortality of the twentieth century, as well as on UK female total cancer mortality, to extract the high-frequency oscillations in the birth cohort time series. US fetal and infant congenital mortality were examined to extend the birth cohorts to modern times. A ∼17-year cycle was detected in all birth cohort series, which spanned approximately 180 years from 1820 to 2000. This suggests a global, environmental cause. To mimic previous work in examining a possible link to cosmic radiation, the 17- to 18-year cycles of the cosmogenic nuclide ¹⁴C, the sunspot double-cycle, neutron monitors, and a compilation of ground-based magnetic field observations were examined in the birth cohort and germ cell cohort time frames. Evidence is presented that optimal alignments with extraterrestrial oscillations occur in the time frame of the germ-cell cohort, one generation before the birth cohorts. Furthermore, the alignment is optimized by accounting for the changes in the maternal age distribution over time. These findings have potential importance to the mechanisms of disease as well as species adaptation and evolution.