Life and the Planet – Part 1

23 05 2011

Life and the Planet meeting at the Geological Society of London

I recently attended the Life and the Planet meeting (May 5-6) held at Burlington House, home of the Geological Society of London, of which I am a fellow. In attendance were many of my friends and colleagues from the Gaia in Oxford meetings, including Jim and Sandy Lovelock, Lynn Margulis, Susan Canney, Tim Lenton, Andrew Watson, David Wilkinson, Anne and Mark Primavesi, and Bill Chaloner.

While the meeting had a Gaia theme, the program consisted of a number of speakers mainly from the geological sciences who are new to the discussion of Gaia. In general the speakers did a fair job of characterizing many of the dramatic shifts in earth’s history, such as the great oxygenation event, snowball earth, and the effects of the first plants on the planet, but many avoided mention of feedbacks, regulation, chaos, and complexity.

The one exception, of course, was the opening talk by James Lovelock. His keynote address was masterful, starting with a concise historical overview of Gaia theory for the many newcomers to the debate. He pointed out that the “atmosphere is almost entirely a biological product”. In his unapologetically alarmist voice he warned of “massively harmful climate change”, and suggested that climate change should mobilize science to geoengineer a fix. He then brought Gaia into the discussion of snowball earth by proposing a set of phytoplankton-driven ocean/atmosphere feedbacks involving sulfur pathways that could help drive the onset and termination of ice age conditions. Acknowledging ocean scientist Brian von Herzen in helping formulate this biotic ice age feedback, he stated “We have no notion if it offers a correct explanation but I put it to you as an example of the need for a whole science approach when seeking explanations of planetary scale phenomenon on a live planet like the Earth” (my bold). He then added, “This is especially true of the next catastrophe, the climate change we are now causing by the excessive excretion of CO2.”

He concluded on some musings on humans’ role in Gaia, saying “As part of the Earth system our job is to help keep our planet habitable and perhaps become a step in the evolution of an intelligent planet.”

The full text of Lovelock’s talk can be found here (h/t Oliver Tickell).

Lovelock’s apocalyptic view of climate change arises from his assumption that the present day living earth system (Gaia) is in a “feverish” state, where many of the self-regulating feedbacks have broken down. Not all of us studying Gaia theory agree with this view. Personally, while I am seeing significant changes occurring in the earth’s forest ecosystems, I do not see convincing evidence that the major temperature-regulating feedbacks of the planet are severely disrupted. While human signatures can be seen in climate change of many regions, I do not agree that the increase in global surface temperatures in recent decades is due mainly to anthropogenic greenhouse gas emissions.

The next speaker was Nick Lane on ‘Energy and the Origin of Life’. He proposed a definition of life as those systems having a driving force (e.g carbon source), metabolism, heredity, integrity, energy, and excretion. He then proposed that alkaline hydrothermal vents are modern day analogs for habitats where life could have originated. He suggested most, if not all, of the life characteristics (above) can be found in the thermodynamics and chemistry of these deep ocean vents.

In the question period afterwards I asked him if there were any microbial life forms associated with the alkaline hydrothermal vents, and he answered yes. So, I’m not sure how you can argue that these systems are analogs to precursors of conditions for life when they already support and are being actively altered by life. Still, I’m in favor of the idea of hydrothermal environments giving rise to life, though I think it more likely that life would have originated in hydrothermal areas at the air-earth-water interface, where there exists a broader range of chemistry and energy sources.

David Schwartzman, presenting ‘Was the Archean Climate Hot or Cold?’, made a passionate case for a very hot Archean (50 to 70 deg C), which he attributes to high CO2 from volcanic outgassing and from reduced weathering sinks due to smaller extent of land areas during the Archean. Curiously, he did not mention the possible warming role of CH4 (methane), another greenhouse gas thought to be abundant in the Archean atmosphere. He claims that the ratio of oxygen isotopes of chert and seawater are a function of, and proxy for, paleo-temperatures, and that analyses of Archean cherts and surrounding rocks point to very high temperatures. He also pointed out that phylogenetics put thermophiles as most primal, suggesting hot conditions under which life originated. He glossed over evidence of Huronian (Archean) glacial episodes at 2.1-2.4 Ga and 2.9 Ga, and disputed other recently published evidence for a cooler Archean climate.

Schwartzman’s thesis is heavily dependent on a large number of unverifiable assumptions of oxygen isotopes in Archean sediments. Other authors (e.g. Kasting et al. 2006) conclude the Archean climate was not much different from the Phanerozoic. The idea that Archean land extent was significantly less than present is widely questioned. The Archean glacial evidence also needs to be somehow reconciled by Schwartzman’s interpretation.

The next three talks focused on mechanisms and conditions associated with the Great Oxidation Event (~2.4 Ga). Euan Nisbet spoke on ‘The origins of (oxygenic) photosynthesis’, and presented evidence from stromatolites for oxygenic photosynthesis arising around 2.9 Ga ago, long before the Great Oxidation Event. This was one of the few papers to propose a biological regulating feedback in the earth system. Nisbet suggested that natural selection on the photosynthetic pathways has controlled the CO2:O2 ratio of the atmosphere and “sustained the Earth’s greenhouse-set surface temperature”.

David Catling’s talk, ‘Causes and Consequences of the Great Oxidation Event’, outlined a mechanism of oxygen buildup involving the loss of planetary hydrogen to space due to methane oxidation (presumably microbial). This caused “irreversible oxidation of the earth, and a secular decline in (atmospheric) methane”. This was followed by the Huronian glaciations (not to be confused with Snowball Earth glaciations which came later, in the Neoproterozoic), the cooling due to a reduction in atmospheric greenhouse gases (CH4 and CO2), and a resulting rise in O2 levels in the atmosphere.

Similarly, Simon Poulton speaking on ‘Paleoproterozoic fluctuations in biospheric oxygenation’ showed compelling evidence for fluctuating ocean oxic states (presumably tied to atmospheric oxygen levels) associated with the three Huronian glaciations. He mentioned that “oxidation of atmospheric methane following biogenic oxygen production has been suggested as a driver for the onset of glaciation”, but added the actual drivers “remain poorly understood”.

In my opinion these three papers on the Great Oxidation Event show just how “greenhouse gas” focused the models are of the earth, especially the early earth. Despite the existence of the Daisyworld model, which shows how simple life forms can regulate planetary surface temperature simply by altering surface albedo (reflectance), with no need to invoke changes in greenhouse gas concentration, scientists studying the early earth are not considering the likelihood that there were vast terrestrial ecosystems comprised of colonial prokaryotic algae, bacteria, and perhaps even fungi in every color and shade forming crusts and gelatinous mats, of the kind proposed by Andrew Knoll of Harvard, that stored water and returned it to the atmosphere. Beside water, these mats likely exchanged oxygen, nitrogen, and sulfur compounds with the atmosphere, and produced rock-dissolving acids that enhanced weathering rates and fluxes of sulfur and iron to the oceans. The existence of these land ecosystems cannot be ignored, though they routinely are ignored in the climate models of the early earth.

(Continued – see Parts 2 & 3)

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4 responses

23 08 2011
David Schwartzman

Very interesting website! Just a few comments on your responses to my presentation. On the potential contribution of methane to generating a hot Archean climate: I had the following on my powerpoint: “Other evidence for a very warm Archean/early Proterozoic (aside from the Huronian) includes: 1) Generally higher weathering intensities then, e.g., paucity of arkoses. These higher intensities would not have occurred if seafloor weathering/C sink was the realplayer, pulling down the temperature, hence this empirical evidence supports a hot climate and high carbon dioxide/methane levels.”
You also say “Schwartzman’s thesis is heavily dependent on a large number of unverifiable assumptions of oxygen isotopes in Archean sediments. Other authors (e.g. Kasting et al. 2006) conclude the Archean climate was not much different from the Phanerozoic. The idea that Archean land extent was significantly less than present is widely questioned. The Archean glacial evidence also needs to be somehow reconciled by Schwartzman’s interpretation.” “Unverifiable assumptions” ? Au contraire, I presented empirical evidence for a near present Archean seawater O18/O16 ratio as well as a host of other supportive evidence for the robustness of the Knauth paleotemperature interpretation of the oxygen isotope record. Most geochemists/geologists now estimate a significantly lower continental land area prior to about 3 billion years ago than now. And yes, the glacial evidence needs to be confronted. This is what I said in my presentation: “the Huronian plausibly explained by the rapid destruction of a methanedominated greenhouse. (Possible glaciation at 2.9 Gya with similar explanation,i.e., transient rise of atmospheric oxygen? Or are these diamictites hypercane deposits, a possibility suggested by Euan Nisbet?).”
I would be happy to send a pdf of my presentation to anyone curious about this debate. Email me at dschwartzman@gmail.com

23 08 2011
David Schwartzman

P.S. I didn’t argue for “reduced weathering sinks” in the hot Archean, on the contrary, at steady-state and for higher volcanic outgassing rates, the weathering sink for carbon must be higher, equal as a flux to the source. But with smaller continental area and lower biotic enhancement of weathering (microbial stabilization of soils) this higher weathering flux must be generated by the combination of much higher atmospheric carbon dioxide levels and climatic temperature than now, i.e., doing the work that biology does now.

23 08 2011
Lee Klinger

Thanks for your comment David. I’m traveling at the moment and will reply when I return. Cheers. Lee

9 09 2011
Lee Klinger

David,
I’m back from an extended stay in the backcountry. Thanks for your patience in awaiting this reply. First, I see that you did mention methane in your presentation and I stand corrected. My pen was simply not fast enough to record it. My revised point is that methane has been proposed to be a major contributor to Archean warming and it is curious to me why you focused so much on carbon dioxide and only briefly mentioned the role of methane.

As for the “unverifiable assumptions” regarding Archean O18/O16 ratios, we all know that these ratios depend on various assumptions such as solar output, oceanic surface area, and cosmic ray flux that cannot be verified for the Archean. Cosmic rays can alter O18/O16 ratios in the atmosphere. For instance, see the abstract here.

Your point that most geochemists/geologists estimate significantly lower continental surface area during the Archean may be right, but the fact remains that there is no good proxy for Archean land area and all estimates are really best guesses.

The Archean glaciations still seem to remain anomalies in your model. You attribute them to reduced methane associated with transient oxidation events. While I agree that oxidation events are somehow linked to these ancient glaciations, I still do not see how your high CO2 model of a hot Archean jives with the glacial record.

Finally, I meant to say “reduced biotic weathering sinks”. I disagree that microbial stabilization of soils would reduce weathering rates. Microbial crusts may reduce erosion, but chemical weathering rates would surely increase.

Thanks again for your comments David. I appreciate your interest in discussing these important matters regarding Gaia theory.

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