The case for a connection between the directionality in Earth’s carbon isotope record and the impact of animal life
The isotopic composition of carbonate carbon (“delta 13C”) in the rock record is a central benchmark for global geochemical change, because it tracks the relative amount of organic and inorganic carbon flowing through the ocean and sediment systems, which connects it to oxygen, ocean alkalinity, temperature (via CO2), and numerous other processes. One of the most immediately obvious features of the delta-13-C record over the entire course of Earth’s history is that the amplitude and period of fluctuation declines over time. In this paper, myself and my colleagues Tais Dahl, Christian Bjerrum and Donald Canfield conduct a comparative study of different mathematical models seeking to explain the nature of such delta-13C fluctuations. We note that many of the more realistic explanations center on low oxygen levels in marine sediments – and we suggest, roughly speaking, that when moving animals evolved and ventilated such sediments, these fluctuations became less likely.
From a broader point of view, this fits in with a general principle first identified by Vladimir Vernadsky; that life is the source of qualitative change in the thermodynamic field of the biosphere. One interpretation of this principle is that when we observe a clear directional change in the geochemical record, a biological influence is the first thing we should check for.
Speculative review on the origin of eukaryotes: Extreme environments and the relative contribution of survival and fecundity to fitness
This paper reviews the fossil evidence and theoretical scenarios pertaining to the second biggest (the first being the origin of life) unanswered question in evolutionary biology; the origin of eukaryotes (large complex cells with nuclei). I suggest that this event illustrates a general principle: Qualitative transitions in biological complexity occur when the physical environment forces survival, rather than fecundity, to become the dominant component of fitness. I also argue that this is relevant to the general idea of novelty as a result of the forcing together of qualitatively different systems that function in similar ways but are composed of different stuff…
Talk at Kreyon Conference 2017: Novelty, historical science, and the limits of objective language
Philosophical arguments are developed concerning the definition and manifestation of novelty, from the perspective of long-term life/environment coevolution:
1) Novelty is most usefully defined as discontinuity in the distribution of cause and effect relationships within time (where a causal relationship is defined in a simple sense as a repetitive temporal association between changes, and a change is in turn defined as the conjunction of identity and temporality).
2) A pragmatic reading of the history of life on Earth (and, more generally, any non-steady state cosmology) justifies the claims that novelty (according to this definition):
(a) Is unequivocally real, but also rare and step-like in nature.
(b) Is the natural phenomenon that imparts direction to time – both in terms of objective application of the scientific method to the past, and the unique importance of time in consciousness/human subjectivity.
(c) Exhibits a closer analogy to symbiosis, in the biological sense, than to any other natural phenomenon.
3) A necessary but not sufficient condition for the occurrence of novelty is the prolonged interaction of systems with similar function but different structure.
(a)Where function is defined, with respect to a given system, as causal repetition unique to, and operating within that system, and structure is defined as repetition dictated by the nature of that system’s material constituents, and imposing constraints on function.
(b) The actual instant at which novelty occurs is identifiable by the fact that changes that initially occur in a temporally inconsistent manner, due to random consequences of the structural difference between the systems, begin to occur consistently at the level of the two initial systems combined.
(c) Both the phenomena of symbiosis and of genetic assimilation may be relevant analogies.
4) The reality of novelty provides a metaphysical grounding for the fact that all objective language must continuously semantically evolve, reconciling the early and late works of Ludwig Wittgenstein, and having implications for philosophical treatments of subjectivity relative to linguistic expression.
5) Although empirically speaking, novelty can only ever be identified retrospectively, it is suggested that development of a mathematical framework for the tracking of causal discontinuity within contexts that give rise bottlenecks of prolonged interactions between unrelated systems, may be of exploratory value.
Book: Natural Novelty: The newness manifest in existence
I have written a book about why new things happen, here’s a pdf. There is a short summary at the front. If you would like to buy a paper copy or higher quality Ebook-style pdf, please visit the amazon profile:
Or buy directly from the publisher (University Press of America) here: https://rowman.com/ISBN/9780761867081/Natural-Novelty-The-Newness-Manifest-in-Existence
Thanks for your interest.
Chicken-egg issues concerning the evolution of eukaryotic cells (paper in press)
Review of hypotheses attempting to explain how and why eukaryotes originated from prokaryotic ancestors. Major theme is the exceptional nature and scale of the change, which lends weight from an evolutionary point of view to the notion that the Proterozoic Earth system must have in some way been “special” in terms of its disposition to produce evolutionary novelty. Discusses a “chicken and egg” problem, whereby respiratory electron transport in multiple mitochondria allows increased free energy availability per cell, which allows an energetically demanding cytoskeleton to be supported – but faces the issue that symbionts are difficult to acquire without phagocytosis, which requires a cytoskeleton in the first place. Suggests a “bottleneck” scenario, in which free living proto-eukaryotes are forced spatially/temporally together, may have increased the probability of endosymbiosis, potentially in connection with the Paleoproterozoic glaciation events.
(Boyle, R.A. “The problem of Eukaryotic origins in relation to the Early/Mid Proterozoic Earth system” Book Chapter, Revolutions in the Early Proterozoic: Tracking Geochemical and Geobiological Change, “Topics in Geobiology”, In Press.)
the significance of animals stirring up mud
Makes the point that bioturbated sediments, ancient and modern, retain more organic phosphate per unit organic carbon than do non-bioturbated sediments (due to microbial polyphosphate sequestration in the oxygen-exposed sediments that result from bioturbation). Because bioturbation evolved at a definable point in time during the early Cambrian, this implies the origin of a concurrent phosphate sink. This in turn implies an oxygen decrease, because oxygen is produced by burial of reduced organic carbon, production of which is limited by phosphorus over long timescales. The oxygen/phosphate decreases were quantified relative to other relevant parameters (weathering, CP ratio of non-bioturbated sediments etc), and a feedback loop was suggested whereby the oxygen decrease induced by bioturbation is self-limiting, because bioturbation-causing animals require oxygen.
Constraints on the chemical composition of the ancient oceans
Addresses the problem of reconciling a Proterozoic “Canfield ocean” scenario (with globally significant euxinia), with the relatively rarity of pyrite-enriched reactive iron during this interval. Uses a simple box model to illustrate how the “electron tower principle” implies that globally significant sulphate reduction necessitates equivalently globally significant nitrate depletion (because denitrifiers will outcompete sulphate reducers). Proposes two distinct geochemical regimes for the low oxygen Proterozoic ocean (nitrate rich/ferruginous and nitrate depleted/euxinic), the latter of which may be partially reverted to in nitrate/oxygen depleted modern day upwelling zones. Suggests that a future empirical cross referencing exercise should find the iron speciation evidence for euxinia to be out of phase in time, with nitrogen isotope evidence for denitrification.