Tyler Volk

Rise of angiosperms as a factor in long-term climatic cooling

By Late Cretaceous or early Tertiary time, the diversification and proliferation of angiosperm-deciduous ecosystems resulted in higher rates of mineral weathering. This increase in the global average weathering rate would have caused a decrease in atmospheric carbon dioxide and, hence, global cooling. The magnitude of this decrease is quantitatively explored here by developing a formulation for global weathering which combines ecosystems that differ in their fractional global coverage and intrinsic rates of weathering. Incorporating this formulation into models—specifically, several previously developed global steady-state models of the geochemical cycle of carbon between the atmosphere and carbonate rocks—gives results that show signifi-cant global cooling from the evolution of the angiosperm-deciduous ecosystems. This cooling may vary from a few degrees up to 10°C. In this way, deciduous ecosystems with high rates of mineral weathering could have contributed to the evolution during the past 100 m.y. of a cooler Earth and thus were a factor in producing conditions that enhanced their global proliferation.

Mass balances for a biological life support system simulation model.

Design decisions to aid the development of future space-based biological life support systems (BLSS) can be made with simulation models. Here we develop the biochemical stoichiometry for 1) protein, carbohydrate, fat, fiber, and lignin production in the edible and inedible parts of plants; 2) food consumption and production of organic solids in urine, feces, and wash water by the humans; and 3) operation of the waste processor. Flux values for all components are derived for a steady-state system with wheat as the sole food source. The large-scale dynamics of a materially-closed (BLSS) computer model is described in a companion paper. An extension of this methodology can explore multi-food systems and more complex biochemical dynamics while maintaining whole-system closure as a focus.

Biotic enhancement of weathering and surface temperatures on earth since the origin of life

Abstract Assuming steady state of carbon dioxide levels in a “pressure-cooker” atmosphere/ocean system (10–20 bars, near 100°C) produced by a land weathering sink and volcanic source (BLAG model), an abiotic Earth model for 3.8 Ga requires present biotic enhancements of weathering to be on the order of 100 or greater, consistent with the limit inferred from experimental and field studies. Using a plausible ratio of the present biotic enhancement (from higher plants) to enhancements produced by microbial activity alone, along with models for continental growth and outgassing rates consistent with geologic evidence, we find that computed surface temperatures hover near 20°C over geologic time, slowly decreasing to present, after a rapid initial decline as a result of microbial colonization of land. Results are consistent with the first possibility for glaciation in the late Archean/early Proterozoic. Useful modeling of climatic evolution, taking into account biotic enhancement of weathering, can now apparently be extended into the Precambrian, assuming operation of the carbonate-silicate buffer.

It is not the entropy you produce, rather, how you produce it

The principle of maximum entropy production (MEP) seeks to better understand a large variety of the Earths environmental and ecological systems by postulating that processes far from thermodynamic equilibrium will ‘adapt to steady states at which they dissipate energy and produce entropy at the maximum possible rate’. Our aim in this ‘outside view’, invited by Axel Kleidon, is to focus on what we think is an outstanding challenge for MEP and for irreversible thermodynamics in general: making specific predictions about the relative contribution of individual processes to entropy production. Using studies that compared entropy production in the atmosphere of a dry versus humid Earth, we show that two systems might have the same entropy production rate but very different internal dynamics of dissipation. Using the results of several of the papers in this special issue and a thought experiment, we show that components of life-containing systems can evolve to either lower or raise the entropy production rate. Our analysis makes explicit fundamental questions for MEP that should be brought into focus: can MEP predict not just the overall state of entropy production of a system but also the details of the sub-systems of dissipaters within the system? Which fluxes of the system are those that are most likely to be maximized? How it is possible for MEP theory to be so domain-neutral that it can claim to apply equally to both purely physical–chemical systems and also systems governed by the ‘laws’ of biological evolution? We conclude that the principle of MEP needs to take on the issue of exactly how entropy is produced.

Interactions of CO2, temperature and management practices: simulations with a modified version of CERES-Wheat.

A new growth subroutine was developed for CERES-Wheat, a computer model of wheat (Triticum aestivum) growth and development. The new subroutine simulates canopy photosynthetic response to CO2 concentrations and light levels, and includes the effects of temperature on canopy light-use efficiency. Its performance was compared to the original CERES-Wheat V-2 10 in 30 different cases. Biomass and yield predictions of the two models were well correlated (correlation coefficient r > 0.95). As an application, summer growth of spring wheat was simulated at one site. Modeled crop responses to higher mean temperatures, different amounts of minimum and maximum warming, and doubled CO2 concentrations were compared to observations. The importance of irrigation and nitrogen fertilization in modulating the wheat crop climatic responses were also analyzed. Specifically, in agreement with observations, rainfed crops were found to be more sensitive to CO2 increases than irrigated ones. On the other hand, low nitrogen applications depressed the ability of the wheat crop to respond positively to CO2 increases. In general, the positive effects of high CO2 on grain yield were found to be almost completely counterbalanced by the negative effects of high temperatures. Depending on how temperature minima and maxima were increased, yield changes averaged across management practices ranged from -4% to 8%.

Did surface temperatures constrain microbial evolution

The proposition that glaciation may not have occurred before the Cenozoic--albeit not yet a consensus position--nevertheless raises for reconsideration the surface temperature history of the earth. Glacial episodes, from the Huronian (2.3 billion years ago; BYA) through the late Paleozoic (320 to 250 million years ago; MYA) have been critical constraints on estimation of the upper bounds of temperature (Crowley 1983, Kasting and Toon 1989). Once removed, few if any constraints on the upper temperature limit other than life remain. Walker (1982) recognized that life provides an upper limit to temperature in the Precambrian. We propose a more radical concept: the upper temperature limit for viable growth of a given microbial group corresponds to the actual surface temperature at the time of the groups first appearance. In particular, we propose here that two major evolutionary developments--the emergence of cyanobacteria and aerobic eukaryotes--can be used to determine surface temperature in the Precambrian, and that only subsequent cooling mediated by higher plants and then angiosperms permitted what may possibly be the earths first glaciation in the late Cenozoic.

Toward a Future for Gaia Theory

The three papers in this issue of Climatic Change (Kirchner, 2002; Kleidon, 2002; Lenton, 2002) are probably the most concentrated effort in recent years by several prominent theoreticians of the biosphere to set forth their views on the current status and future of Gaia theory. (Also see the forthcoming volume by M.I.T. Press of the proceedings from the Second Chapman Conference on the Gaia Hypothesis, Valencia, Spain, 2000.) The three papers offer strikingly different renderings. Axel Kleidon asks whether life on global scales enhances itself by improving environmental conditions through its activities. His analysis suggests ‘yes.’ He further recommends that primary production measured in carbon units should be utilized as a ‘metric’ (my term) for Gaia theory. In contrast, Timothy Lenton focuses not as much on environmental parameters but on whether a global system with life, compared to a sterile planet, will be more resistant to change and also more resilient in its rapidity of response to change. Lenton concludes, tentatively at least, that the Gaia system does enhance regulation and that this regulation will tend to accumulate over time. The message in the third paper, by James Kirchner, runs counter to both Kleidon and Lenton. Kirchner uses evolutionary arguments to show why we should expect Gaia neither to be more stably regulated than an abiotic system nor produce an enhanced environment for life. Overall, I am most in agreement with Kirchner. As I will emphasize, the dynamics of evolutionary adaptation have far too often been neglected by Gaia theorists. In this essay I will concentrate first on the arguments advanced by Kleidon and Lenton, looking both at their shortfalls and positive offerings. Eventually I will try to use ideas from all three papers to sketch out what I see as tasks for the future of Gaia theory, which involves the ongoing search for general principles of the biosphere.

A modular BLSS simulation model

The coordination of material flows in Earths biosphere is largely made possible by the buffering effect of huge material reservoirs. Without similarly-sized buffers, a bioregenerative life support system (BLSS) for extraterrestrial use will be faced with coordination problems more acute than those in any ecosystem found on earth. A related problem is BLSS design is providing an interface between the various life-support processors, one that will allow for their coordination while still allowing for system expansion. Here we present a modular model of a BLSS that interfaces system processors only with the material storage reservoirs, allowing those reservoirs to act as the principal buffers in the system and thus minimizing difficulties with processor coordination. The modular nature of the model allows independent development of the detailed submodels that exist within the model framework. Using this model, BLSS dynamics were investigated under normal conditions and under various failure modes. Partial and complete failures of various components, such as the waste processor or the plants themselves, drive transient responses in the model system, allowing us to examine the effectiveness of the system reservoirs as buffers. The results from simulations of this sort will help to determine control strategies and BLSS design requirements. An evolved version of this model could be used as an interactive control aid in a future BLSS.

Toward a science of metapatterns: building upon Bateson's foundation

Purpose – Gregory Bateson defined a metapattern as a “pattern of patterns.” But, what did he mean by metapattern (which he used only once)? Can there be a meta‐science, in which metapatterns are its objects or principles? The authors explore these issues.Design/methodology/approach – The authors review examples of Batesons “great pattern” of “combination,” which the authors call the binary. Bateson showed that binary is the minimal solution to the problem of gaining new characteristics by combining parts into a larger whole. Thus, binary is clearly a metapattern, a discipline‐transcending structural and functional principle. The authors select parts of Batesons writings to highlight his search for other great patterns, some of which correspond with those developed by T. Volk.Findings – The authors suggest that the basis for a science of metapatterns is the following: functional patterns that confer advantages on the systems that possess those patterns can converge, in a meta‐realm that includes all of w...

Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids?

Eight circular geologic structures ranging from ∼3 to 17 km in diameter, showing evidence of outward-directed radial deformation and intensive brecciation, lie within a linear swath ∼15 km wide along a straight line stretching ∼700 km across the United States from southern Illinois through Missouri to eastern Kansas. Based on their similar geological characteristics and the presence of diagnostic and/or probable evidence of shock, these structures, once classified as ‘cryptovolcanic’ or ‘cryptoexplosion’ structures, are more confidently ascribed to hypervelocity impact. No other similar occurrence of aligned features is known, and we calculate the probability of a chance alignment to be <10−9. The unusual alignment suggests that the features are coeval and related to a multiple impact event, with a best-constrained late Mississippian-early Pennsylvanian (∼330–310 Myr) age. Calculations suggest that the proposed impact-crater chain is unlikely to have been formed by an incoming impactor disrupted by terrestrial or lunar tidal effects, and may have been the result of a string of asteroidal or cometary objects produced by breakup within the inner Solar System.