The Case for a Hot Early Earth(Climate) David W. Schwartzman Department of Biology Howard University, Washington, DC email@example.com Faint Early Sun Conference, April 9, 2012, Baltimore MD
A compelling case for a hot Archean (50-70 deg C) (And early Proterozoic aside from the Huronian) : Sedimentary chert oxygen and silicon isotopic record from the same samples and evidence for nearly constant seawater O18 /O16 ratio going back into the Archean (even the Hadean?). Knauth, L.P. and D.R. Lowe, 2003, Geol. Soc. Am. Bull. 115: 566–580. Knauth, L.P., 2005, Palaeogeog. Palaeoclim. Palaeoecol. 219: 53-69.
Challenges to hot Archean interpretation of Oxygen Isotope Record: 1) Burial temperatures recorded 2) (All) Archean cherts are hydrothermal 3) Archean seawater isotopically lighter than present ocean The silicon isotopic record appears to rule out resetting of climatic record by reequilibration during burial. ( Robert, F. and M. Chaussidon, 2006, Nature 443, 969-972.)
Evidence for near present seawater O18 /O16 ratio back into the Archean includes: 1) Paleozoic seawater is not significantly lighter than the present: direct measurement of fossil seawater from salt inclusions (Knauth, L.P. and S.K. Roberts, 1991, Geochemical Society Special Publication No. 3, 91- 104). (Same conclusion from clumped isotope study, Eiler, 2006) 2) Inferred from the geologic record of ancient seawater-altered oceanic crust (ophiolites, their ecologite proxies, greenstones)
Buffering of oxygen isotopic ratio of seawater by reaction with oceanic crust over geologic time Low temperature: Oceanic crust gains O18 relative to seawater High temperature: Oceanic crust loses O18, coming closer to seawater O18/O16 ratio
Jacob, D.E., 2004, Lithos 77: 295-316 Isua ophiolite (3.8 Ga): : 5.7 - 9.9(Furnes et al., 2007) Onverwacht greenstone (3.3-3.5 Ga): 3 -14(Hoffman et al., 1986) Joruma ophiolite (1.95 Ga): 1.4 - 8.5(Muehlenbachs et al., 2004) O18-depleted ecologites from Roberts Victor: consistent with subducted oceanic crust equilibrating at high temperature with seawater (Greau et al., 2011)
Other evidence for near present seawater O18 /O16 ratio back into the Archean/Hadean 2) Iceland, a subaerial, shallow ridge crest shows supply of O18 to hydrosphere even by light meteoric water interaction (Gantason and Muehlenbachs, 1998). 3) Archean and Proterozoic volcanogenic massive sulfide deposits with ore fluids on the order of 300 deg C and del O 18 = 0 per mil, again no evidence of very light seawater (personal communication, Muehlenbachs) 4) As Robert/Chaussidon pointed out, Karhu and Epstein’s (1986) chert-phosphate pairs give seawater values close to present day (+/- 5 per mil) back into the Archean, even if the temperatures of equilibration for some samples may be higher than the sediment/seafloor interface (note: their cherts were not necessarily the heaviest for each age, hence diagenetic equilibration temperatures are probable for several samples). 5) Hydrogen isotopic composition inferred from del D values measured from 2 Ga ophiolite-like complex (Lecuyer et al., 1996, Geology 24: 291-294). 1) Serpentinite (3.8 Ga) study (Pope et al., 2012, PNAS 109 (12) 4371-4376).
Conclusions Archean/Proterozoic ophiolites Joruna (2 Ga), Isua (3.8 Ga) and 3.3-3.5 Ga Onverwacht greenstone (Hoffman et al., 1986) have oxygen isotope patterns similar to Phanerozoic. Archean ecologite proxies for depleted/enriched seawater-altered oceanic crust (Jacob, 2004) with abundant depleted values, clear evidence of high temperature interaction with seawater. Similarly, high temperature alteration phases in the ophiolites show no evidence of equilibration with del O 18-depleted seawater. (Turner et al., 2007, Boron and oxygen isotope evidence for recycling of subducted components over the past 2.5 Gyr. Nature 447: 702-705) Hence the buffer was similar to now, O18/O 16seawater ratio close to present value.
Rosing et al., 2010, Nature 464, 744-747. Phase relations of iron minerals (magnetite, hematite, siderite) in Archean banded iron formations: Their conclusion: The Archean atmospheric carbon dioxide level was far too low to sustain a hot climate. However, I submit their reasoning is circular, since they assumed a temperature near 25 deg C to derive their low carbon dioxide level. On the same phase diagram, hot Archean temperatures on the order of 60-80 deg C are consistent with much higher carbon dioxide levels in the atmosphere.
But the triple point at 70 deg C is above the Faint Early Sun Constraint, not below it: PCO2 = 0.3 bars, log PCO2 = -0.52 x Figure provided by Rosing et al. in rebuttal to my critique
Another very recent challenge Som et al. (2012) Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints. Nature 484, in press. They claim "Our result rules out very high Archaean ocean temperatures of 70 C–85 C (refs 13 and 31), because these would necessitate about 2–6 bar of carbon dioxide8 plus 0.3–0.6 bar of water vapour, increasing barometric pressure far beyond the upper limit found here." They are referring to temperatures inferred from the earlier oxygen isotopic record of chert (3.5 to 3.0 Ga) assuming a CO2-dominated greenhouse. However, assuming their limit on air density is robust, it is consistent with the onset of a CH4-dominated greenhouse at about 2.7-2.8 Ga, with emergence of oxygenic photosynthesis boosting marine productivity and methane production. (Schwartzman et al., 2008, Astrobiology 8 (1): 187-203). Evidence for significant atmospheric methane at 2.7 Ga: e.g., Hayes (1994), Zherkle et al. (2012) A bistable organic-rich atmosphere on the Neoarchaean Earth. Nature Geoscience, in press.
More evidence for a very warm Archean 1) Cold Archean is hard to explain in the context of the long term carbon cycle: higher outgassing rates of carbon dioxide, smaller land areas and weaker biotic enhancement of weathering in Archean than present, taking into account the fainter Archean sun in climate modeling and higher weatherability of mafic crust. (Schwartzman, 1999 2002; see supplementary slide). Note as well the generally higher Archean weathering intensities, implying seafloor weathering was not driving the C sink, reducing temperature, hence a hot climate and high carbon dioxide/methane levels. 2) High CO2 levels prior to the first documented evidence of likely atmospheric methane at 2.8 Gya, consistent with the apparent requirements for the formation of Mn-bicarbonate clusters leading to oxygenic photosynthesis, i.e., high bicarbonate and therefore high CO2 levels are necessary (on order of 1 bar, pH of about 6.5). (Dismukes et al., 2001, PNAS 98:2170–2175). Note: Mn-bicarbonate and Cl complexing and lower pH increases Mn solubility in seawater (Dismukes and Blankenship, 2005). 3) No apparent glaciations for over a billion years (2 Gya to NeoProterozoic snowball), with the Huronian plausibly explained by the rapid destruction of a methane- dominated greenhouse. (Probable (?) glaciation at 2.9 Gya with similar explanation, i.e., transient rise of atmospheric oxygen?; see Ono et al. (2006) South African Jour. Geology 109: 97-108. Or are these Pongola diamictites, reworked impact deposits ?)
Why is there now the equivalent of 50-60 bars of CO2 in the crust as carbonate and reduced organic carbon, if seafloor weathering/carbonation of oceanic basalt drew down the atmospheric CO2, sinking most of it in the mantle, instead of degassing it back to the atmosphere/ocean during subduction? Modeling the history of juvenile degassing can explain how this 50-60 bar equivalent of crustal sedimentary carbon is consistent with high steady-state atmospheric pCO2 levels and surface temperatures prior to about 2.7 Ga. (see p.364-5, Schwartzman, D. and T. Volk, 1991, Biotic enhancement of weathering and surface temperatures on Earth since the origin of life, Palaeogeogr. Palaeoclimatol. Palaeoecol. (Global and Planetary Change Sect.) 90, 357-371).
Other evidence for a very warm Archean 1) Generally higher weathering intensities then, e.g., paucity of arkoses. E.g., Simpson et al., 2012, 3.2 Ga eolian deposits from the Moodies Group, Barberton Greenstone Belt, South Africa: Implications for the origin of first-cycle quartz sandstones. Precambrian Research, in press; Corcoran, P.L. and Mueller, W.U. (2004) Aggressive Archaean weathering. In: The Precambrian Earth: Tempos and Events, Developments in Precambrian Geology12, edited P.G. Eriksson, W.A. Altermann, D.R. Nelson, W.U. Mueller, and O. Catuneaunu, Elsevier, Amsterdam, pp. 494–504. 2) Highly stratified oceans apparently persisting until the mid Proterozoic (see Lowe, D.R., 1994, Early environments: Constraints and opportunities for early evolution. In: Early Life on Earth. Nobel Symposium No.84. (ed. S. Bengtson) pp. 24-35, Columbia University Press. N.Y.
High Hadean/Archean pCO2 levels in Atmosphere/Ocean Lichtenegger et al., 2010, Aeronomical evidence for higher CO2 levels during Earth’s Hadean epoch. Icarus 210: 1–7. (protected atmosphere from solar wind induced loss) Nutman et al., 2012, Waves and weathering at 3.7 Ga: Geological evidence for an equitable terrestrial climate under the faint early Sun. Australian Journal of Earth Sciences 59 (2): 167-176. Dauphas et al., 2007, Identification of chemical sedimentary protoliths using iron isotopes in the >3750 Ma Nuvvuagittuq supracrustal belt, Canada. Earth and Planetary Science Letters 254 (3–4): 358-376. Rouchon, V. and B. Orberger, 2008, Origin and mechanisms of K–Si-metasomatism of ca. 3.4–3.3 Ga volcaniclastic deposits and implications for Archean seawater evolution: Examples from cherts of Kittys Gap (Pilbara craton, Australia) and Msauli (Barberton Greenstone Belt, South Africa). Precambrian Research 165: 169–189. Rouchon et al., 2010, Diagenetic Fe-carbonates in Paleoarchean felsic sedimentary rocks (Hooggenoeg Formation, Barberton greenstone belt, South Africa): Implications for CO2 sequestration and the chemical budget of seawater. Precambrian Research 172: 255–278. Shibuya et al., 2010, Highly alkaline, high-temperature hydrothermal fluids in the early Archean ocean. Precambrian Research 182: 230–238. ____ 2012, Depth variation of carbon and oxygen isotopes of calcites in Archean altered upper oceanic crust: Implications for the CO2 flux from ocean to oceanic crust in the Archean. EPSL 321-322: 64–73.
New evidence for a hot Archean climate Fralick and Carter (2011) Neoarchean deep marine paleotemperature: Evidence from turbidite successions. Precambrian Research 191: 78– 84. Relative scarcity of ripple marks in these sediments (2.7 Ga) imply lower viscosity of seawater, hence higher temperatures consistent with a hot Archean climate.
Phylogeny and Temperature Note the apparent absence on molecular phylogenetic trees of deeply-rooted mesophiles/ psychrophiles. If Archean temperatures were similar to the Phanerozoic, then some of the low-temperature prokaryotes should be grouped near the root with the hyperthermophiles/thermophiles. Phylogenetic tree based on rRNA sequences (Lineweaver & Schwartzman 2004, Cosmic Thermobiology, based on Pace, N.R., 1997, Science, 276: 734-740.)
Inferred paleotemperatures from resurrected (elongation) proteins(Gaucher et al., 2008, Nature 451: 704-707.) Consistent with hot Archean, e.g., cyanobacteria emerging at about 60 deg C at 2.8 Ga. (Schwartzman, D., Caldeira, K., and A. Pavlov, 2008, Astrobiology 8 (1): 187-203.) More support for hot Archean temperatures from molecular studies: Boussau et al., 2008, Parallel adaptations to high temperatures in the Archaean eon. Nature 456: 942 – 945. Perez-Jimenez et al., 2011, Single-molecule paleoenzymology probes the chemistry of resurrected enzymes. Nature Structural & Molecular Biology 18: 592–596.
Upper temperature limits for growth of living organisms, approximate times of their emergence Group Approximate upper Time of temperature limit (“Tmax”) Emergence (oC) (Ga) “Higher” kingdoms: Plants 50 0.5-1.5 Metazoa (Animals) 50 0.6-1.5 Fungi 60 0.6-1.5 Eucaryotes 60 2.1-2.8 Procaryotes Phototrophs 70 >3.5 Hyperthermophiles >100 >3.8 (Temperatures from Brock & Madigan, 1991)
Sequence of organismal emergence times and Tmax Tmax values at emergence are consistent with the chert paleo- temperatures, and the more recent emergence of psychrophiles, hence little or no ice before the step down in temperature at about 1.4 Gya (aside from the Huronian; mesophiles emerging then would be likely wiped out by a return to near thermophilic temperatures). Oxygen levels alone cannot explain the big delay in the appearance of the "Higher" Kingdoms; Note the presence of high oxygen in surface microenvironmentssuch as cyanobacterial mats, going back to 2.7 Ga, as well as the recent discovery of anoxic metazoa*). *Danovaro, R. et al., 2010, The first metazoa living in permanently anoxic conditions. BMC Biology 2010, 8:30
Temperature History of Biosphere Explosion of Biodiversity
Warm-blooded Animals Tbody near 40 oC: provides energy for large brain; Tbody - Tclimate determines efficiency of heat loss from brain Future Past Tmax Metazoa 50 o C Tmax Vertebrates 40 o C Window for Maximum Encephalization
Lineweaver, C.H. and D. Schwartzman, 2004, Cosmic Thermobiology. In: Origins (ed. J. Seckbach), 233-248, Kluwer. Schwartzman, D., 1999, 2002 (updated paperback), Life, Temperature and the Earth: The Self-Organizing Biosphere. Columbia Univ. Press. Schwartzman, D.W., 2008, Coevolution of the Biosphere and Climate, In: Encyclopedia of Ecology (S.E. Jorgensen and B. Fath, eds), pp. 648-658, 1st Edition, Elsevier B.V., Oxford. Schwartzman, D.W. and L. P. Knauth, 2009, A hot climate on early Earth: implications to biospheric evolution. In: K.J. Meech et al. (eds.) Bioastronomy 2007: Molecules, Microbes, and Extraterrestrial Life, Astronomical Society of the Pacific Conference Series Vol. 420, San Francisco, pp. 221-228. Schwartzman, D. and C.H. Lineweaver, 2004, Temperature, Biogenesis and Biospheric Self-Organization. In: Non-Equilibrium Thermodynamics and the Production of Entropy:Life, Earth, and Beyond (eds. A. Kleidon and R. Lorenz), chapter 16, Springer Verlag. Schwartzman D, Middendorf M., and M.Armour-Chelu, 2009, Was climate the prime releaser for encephalization? Climatic Change 95, Issue 3: 439-447. References
Schwartzman, D. (1999, 2002) Life, Temperature and the Earth: The Self-Organizing Biosphere. Columbia Univ. Press.
(O18/O16) chert (SiO2) = f (temperature) (O18/O16) seawater
Hren et al., 2009, Nature 462: 205-208. O and H isotopes in 3.42 Ga Archean cherts: Their conclusion: Cherts formed in waters below 40 deg C. However, the hydrogen extracted in their analysis is not likely derived from in-situ OH groups, rather is an artifact of sample preparation, and as such represented modern, not Archean hydrogen isotopic ratios. (Paul Knauth, personal communication)
Blake et al., 2010, Nature 464: 1029-1032. • Isotopic analysis of Archean phosphate inclusions in chert: • Their conclusion: Inclusions crystallized in a ocean with similar • temperature to the present (26 to 35 deg C). But the O isotopic of • the host chert was not measured, which very likely equilibrated with the • minute phosphate inclusions during metamorphism, thereby changing • the original oxygen isotopic ratio in the phosphate grains (Paul Knauth, • personal communication). Nevertheless, they concluded the Archean • seawater oxygen isotopic composition was similar to the present, in • direct contradiction to the significantly lower O18/O16 ratio inferred in • Hren et al.’s analysis required to give their low temperatures.
Climatic cooling as a necessary condition for encephalization Schwartzman, D. and G. Middendorf, 2000, Biospheric cooling and the emergence of intelligence, In: A New Era in Bioastronomy, ASP Conference Series, Vol. 213, (G. Lemarchand and K. Meech, eds.), 425-429.
Implications to biotic and biospheric evolution: 1) Temperature constraint on emergence of major organismal groups. • 2) Atmospheric pO2 constraint on macroeucaryotes, including metazoa • in the Phanerozoic (Berner et al., 2007, Science 316: 557-558). • 3) Atmospheric pCO2 constraint on emergence of cyanobacteria, • lichens and leaves (megaphylls) in Devonian. • 4) A geophysiology of biospheric evolution, likewise on Earth-like • planets around Sun-like stars. • The highest level of niche-construction is the biosphere(see John • Odling-Smee, 2007, Niche inheritance: a possible basis for classifying multiple • inheritance systems in evolution. Biological Theory 2(3) 276–289.)
Quasi-determinism Multiple outcomes from the same initial conditions ? Randomness in impact history, multiple attractor states in mantle convection and steady-state climate regimes. Vary initial conditions: Will different geochemical environments (e.g.,trace element concentrations) generate different biochemistries, hence different temperature limits to phototrophy, oxygenic photosynthesis, “complex” life? Since a variety of geochemical environments likely existed on early Earth, were other biochemistries lost? Future: Compute, create and observe alternative biochemistries