Snowball Earth and biological weathering enhancement

(work in progress)

Integrated geological evidence suggests that grounded ice sheets occurred at sea level across all latitudes during two intervals within the Neoproterozoic era; the “snowball Earth” (SBE) events. Glacial events at ~730 and ~650 million years ago (Ma) were probably followed by a less severe but nonetheless global-scale glaciation at ~580Ma, immediately preceding the proliferation of the first fossils exhibiting unambiguous animal-like form. Existing modeling identifies weathering-induced CO2 draw-down as a critical aspect of glacial inception, but ultimately attributes the SBE phenomenon to unusual tectonic boundary conditions. Here we suggest that the evident directional decrease in Earth’s susceptibility to a SBE suggests that such a-directional abiotic factors are an insufficient explanation for the lack of SBE events since ~580 Ma. Instead we hypothesize that the terrestrial biosphere’s capacity to sustain a given level of biotic weathering-enhancement under suboptimal/declining temperatures, itself decreased over time: because lichens (with a relatively robust tolerance of sub-optimal temperatures) were gradually displaced on the land surface by more complex photosynthetic life (with a narrower temperature window for growth). We use a simple modelling exercise to highlight the critical (but neglected) importance of the temperature sensitivity of the biotic weathering enhancement factor and discuss the likely values of key parameters in relation to both experiments and the results of complex climate models. We show how the terrestrial biosphere’s capacity to sustain a given level of silicate-weathering-induced CO2 draw-down is critical to the temperature/greenhouse forcing at which SBE initiation is conceivable. We do not dispute the importance of low degassing rate and other tectonic factors, but propose that the unique feature of the Neoproterozoic was biology’s capacity to tip the system over the edge into a runaway ice-albedo feedback; compensating for the self-limiting decline in weathering rate during the temperature decrease on the approach to glaciation. Such compensation was more significant in the Neoproterozoic than the Phanerozoic due, ultimately, to changes in the species composition of the weathering interface over the course of evolutionary time.

https://www.biorxiv.org/content/early/2018/06/29/359422.full.pdf

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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.

bioturb d13C final

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…

eukaryotes final

 

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.

http://kreyon.net/kreyonConference/

kreyon talk rich

 

 

 

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:

https://www.amazon.co.uk/Natural-Novelty-Newness-Manifest-Existence/dp/0761867082

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.

NN

 

 

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.)

BookChapterRBFinal

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.

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