Archaean Earth Research Articles

Diverse volcanism and crustal recycling on early Mars

The relatively well-preserved ancient crust of Mars provides a natural window into early planetary evolution not available on Earth due to sustained tectonic recycling and erosion on this planet. Mars has generally been considered a one-plate basaltic planet, though recent evidence suggests magmatic evolution resulting in felsic crust might have occurred sporadically. Here we show multiple lines of evidence for diverse volcanism and complex volcanotectonics in the southern highlands of Mars within and around the ∼3.5–4-billion-year-old Eridania basin. Infrared remote sensing reveals bimodal volcanism consisting of olivine-bearing basalts and voluminous, widespread dacitic (64–69% SiO2, and possibly higher) volcanic deposits within a region of high crustal potassium. The diverse igneous compositions are associated with an extraordinary number and morphological range of volcanic structures, including domes, stratovolcanoes, calderas and pyroclastic shields occurring proximal to large (hundreds of kilometres in diametre) basins within the Eridania region. The 2–4 km-deep topographically concave-up basins have crustal thicknesses 10–20 km thinner than adjacent terrain and disrupt patterns of deeply seated remnant crustal magnetism. The Eridania basins may represent ancient episodes of crustal recycling via lithospheric delamination in which altered, hydrated volcanic materials were cycled downward and melted resulting in magmatic evolution analogous to pre-plate tectonic processes on the Archaean Earth.

Evidence of Earth’s Oldest Glaciers Found in South Africa

The ancient glaciers hint at an Archaean Earth that may have looked similar in some ways to our own time.

Isotopic constraints on lightning as a source of fixed nitrogen in Earth’s early biosphere

Bioavailable nitrogen is thought to be a requirement for the origin and sustenance of life. Before the onset of biological nitrogen fixation, abiotic pathways to fix atmospheric N2 must have been prominent to provide bioavailable nitrogen to Earth’s earliest ecosystems. Lightning has been shown to produce fixed nitrogen as nitrite and nitrate in both modern atmospheres dominated by N2 and O2 and atmospheres dominated by N2 and CO2 analogous to the Archaean Earth. However, a better understanding of the isotopic fingerprints of lightning-generated fixed nitrogen is needed to assess the role of this process on early Earth. Here we present results from spark discharge experiments in N2−CO2 and N2−O2 gas mixtures. Our experiments suggest that lightning-driven nitrogen fixation may have been similarly efficient in the Archaean atmosphere, compared with modern times. Measurements of the isotopic ratio (δ15N) of the discharge-produced nitrite and nitrate in solution show very low values of −6‰ to −15‰ after equilibration with the gas phase with a calculated endmember composition of −17‰. These results are much lower than most δ15N values documented from the sedimentary rock record, which supports the development of biological nitrogen fixation earlier than 3.2 billion years ago. However, some Paleoarchean records (3.7 billion years ago) may be consistent with lightning-derived nitrogen input, highlighting the potential role of this process for the earliest ecosystems. Spark discharge experiments suggest lightning was not the main source of bioavailable nitrogen for the established Archaean biosphere, but could have been significant for Earth’s earliest ecosystems.

Light-independent anaerobic microbial oxidation of manganese driven by an electrosyntrophic coculture.

Anaerobic microbial manganese oxidation (AMMO) has been considered an ancient biological metabolism for Mn element cycling on Archaean Earth before the presence of oxygen. A light-dependent AMMO was recently observed under strictly anoxic conditions, providing a new proxy for the interpretation of the evolution of oxygenic photosynthesis. However, the feasibility of biotic Mn(II) oxidation in dark geological habitats that must have been abundant remains unknown. Therefore, we discovered that it would be possible to achieve AMMO in a light-independent electrosyntrophic coculture between Rhodopseudomonas palustris and Geobacter metallireducens. Transmission electron microscopy analysis revealed insoluble particle formation in the coculture with Mn(II) addition. X-ray diffraction and X-ray photoelectron spectroscopy analysis verified that these particles were a mixture of MnO2 and Mn3O4. The absence of Mn oxides in either of the monocultures indicated that the Mn(II)-oxidizing activity was induced via electrosyntrophic interactions. Radical quenching and isotopic experiments demonstrated that hydroxyl radicals (•OH) produced from H2O dissociation by R. palustris in the coculture contributed to Mn(II) oxidation. All these findings suggest a new, symbiosis-dependent and light-independent AMMO route, with potential importance to the evolution of oxygenic photosynthesis and the biogeochemical cycling of manganese on Archaean and modern Earth.

Earth’s oldest tsunami deposit? Early Archaean high‐energy sediments in the ca 3.48 Ga Dresser Formation (Pilbara, Western Australia)

AbstractDynamic sedimentary processes are a key parameter for establishing the habitability of planetary surface environments on Earth and beyond and thus critical for reconstructing the early evolution of life on our planet. This paper presents a sedimentary section from the ca 3.48 Ga Dresser Formation (Pilbara Craton, Western Australia) that contains high‐energy reworked sediments, possibly representing the oldest reported tsunami deposit on Earth to date. Field and petrographic evidence (e.g. up to 20 cm large imbricated clasts, hummocky bedding, Bouma‐type graded sequences) indicate that the high‐energy deposit represents a bi‐directional succession of two debrite–turbidite couplets. This succession can best be explained by deposition related to passage and rebound of tsunami waves. Sedimentary processes were possibly influenced by highly dense silica‐rich seawater. The tsunami was probably triggered by local fault‐induced seismic activity since the Dresser Formation was deposited in a volcanic caldera basin that experienced syndepositional extensional growth faulting. However, alternative triggers (meteorite impact, volcanic eruption) or a combination thereof cannot be excluded. The results of this work indicate a subaquatic habitat that was subject to tsunami‐induced high‐energy disturbance. Potentially, this was a common situation on the early Archaean Earth, which experienced frequent impacts of extraterrestrial bodies. This study thus adds to the scarce record of early Archaean high‐energy deposits and stresses the relevance of high‐energy depositional events for the early evolution of life on Earth.

The future lifespan of Earth’s oxygenated atmosphere

Earth's modern atmosphere is highly oxygenated and is a remotely detectable signal of its surface biosphere. However, the lifespan of oxygen-based biosignatures in Earth's atmosphere remains uncertain, particularly for the distant future. Here we use a combined biogeochemistry and climate model to examine the likely timescale of oxygen-rich atmospheric conditions on Earth. Using a stochastic approach, we find that the mean future lifespan of Earth's atmosphere with oxygen levels more than 1% of the present atmospheric level is 1.08+-0.14 billion years. The model projects that a deoxygenation of the atmosphere, with atmospheric oxygen dropping sharply to levels reminiscnet of the Archaean Earth, will most probably be triggered before the inception of moist greenhouse conditions in Earth's climate system and before the extensive loss of surface water from the atmosphere. We find that future deoxygenation is an inevitable consequence of increasing solar fluxes, whereas its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean-atmosphere-crust system. Our results suggest that the planetary carbonate-silicate cycle will tend to lead to terminally CO2-limited biospheres and rapid atmospheric deoxygenation, emphasizing the need for robust atmospheric biosignatures applicable to weakly oxygenated and anoxic exoplanet atmospheres and highlighting the potential importance of atmospheric organic haze during the terminal stages of planetary habitability.

From the LIPS of a serial killer: Endogenic retardation of biological evolution on unstable stagnant-lid planets

Geological data imply plate tectonics was not active on the Archaean Earth pre-2.5 ​Ga. Key arguments include: the absence from the Archaean rock record of ophiolites and high-pressure metamorphic rocks; the rarity of Archaean andesites and lahars; the absence of arc-like, source-metasomatic, trace element signatures in Archaean calc-alkaline magmatic suites; and fundamental differences in overall structural style and constituent lithologies. Conversely, unstable stagnant-lid models better account for many features of Archaean geology. Thermo-mechanical models imply many unstable stagnant-lid planets would experience mobile-lid phases linked to periodic mantle overturns of 30–100 million years duration, separated by stable-lid phases lasting 100–300 My. Mantle overturn upwelling zones would be characterized by high magma fluxes that may have generated continental nuclei, and would have reworked and resurfaced tracts of pre-existing oceanic and continental lithosphere. Overturns would also have generated large-scale lateral mantle flow patterns that would have pushed against the sub-continental lithospheric mantle keels underlying continents, and so induced continental drift and orogenesis, allowing mobile-lid behaviour despite the absence of plate-boundary forces such as slab pull. Major resurfacing of Earth’s surface during overturns would have heated the hydrosphere and atmosphere, with many negative impacts on biota. The high magmatic fluxes associated with mantle overturn events are likely to have induced periodic mass extinctions that may have retarded biological evolution on Earth. Evolutionary progress towards more complex metazoan organisms may only have been possible after the more efficient plate tectonic cooling system helped create a stabler, more temperate planet; although causal relationships remain uncertain. Did the start of a plate tectonic, mobile-lid cooling system on Earth gradually end (or moderate) mantle overturn behaviour? Or was the world-girdling plate tectonic system only allowed to begin because ‘other factors’ gradually acted to suppress mantle overturns during the Proterozoic? These ‘other factors’ include: secular decay of radioactive isotopes, scavenging of radioactive elements into continents, and shrinkage of the fertile lower mantle reservoir that fed early overturns. When overturn behaviour ended on Earth is also uncertain. The 2.1–1.9 ​Ga magmatic and tectonic pulse on Earth is plausibly interpreted as an Archaean-style mantle overturn, but more research is needed to determine whether the Large Igneous Provinces (LIPs) of the Meso- and Neo-Proterozoic are as well. It is predicted that Earth-sized exoplanets with surface water and chondritic mantle compositions will spend at least the first 2 ​Ga of their evolution as unstable stagnant-lid planets, with periodic overturns preventing evolution of complex metazoan organisms. Many such planets could remain trapped in this cooling mode, with only rare cases transitioning into the more efficient plate tectonic cooling mode. If correct, this greatly decreases the probability that complex metazoans are present elsewhere in the universe.

Solvated-electron production using cyanocuprates is compatible with the UV-environment on a Hadean-Archaean Earth.

UV-driven photoredox processing of cyanocuprates can generate simple sugars necessary for prebiotic synthesis. We investigate the wavelength dependence of this process from 215 to 295 nm and generally observe faster rates at shorter wavelengths. The most efficient wavelengths are accessible to a range of potential prebiotic atmospheres, supporting the potential role of cyanocuprate photochemistry in prebiotic synthesis on the early Earth.

Enantiomeric excess by magnetic circular dichroism in Archaean atmosphere

Evolution of homochirality requires an initial enantiomeric excess (EE) between right and left-handed biomolecules. We show that magnetic circular dichroism (MCD) of sun’s ultraviolet C light by oxygen in Archaean earth’s anoxic atmosphere followed by chirally selective damage of biomolecules due to circular dichroism (CD) can generate EE of correct handedness. Our calculation of EE uses published data for CD of biomolecules and accepted magnitude for Archaean earth’s magnetic field. Independent of atmospheric oxygen concentration calculated EE has the same sign for all pyrimidine nucleosides which is opposite to that for amino-acids. Purine nucleosides have smaller EE values with opposite sign to pyrimidines but are less susceptible to UV damage. Homochirality is explained by origin of prebiotic life in one hemisphere of earth and its evolution to EE ~ ± 1 before reversal of terrestrial magnetic field. Chirality of biomolecules is decided by the direction of magnetic field where prebiotic life originated on Archaean earth.

Microblock amalgamation in the North China Craton: Evidence from Neoarchaean magmatic suite in the western margin of the Jiaoliao Block

The Archaean Earth is considered to have been characterized by microcontinents that formed, dominantly, through the accretion of oceanic arcs and plateaus. The North China Craton (NCC) provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the Archaean. Here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks, the Jiaoliao Block that forms part of the composite Eastern Block of the NCC. We present petrological, geochemical and zircon U–Pb geochronological data from the Taipingzhai charnockite suite, and associated amphibolites, metagabbros and orthogneisses from the Qianxi Complex. Geochemically the rocks show a wide range of SiO2 (charnockite suite: 52.57–75.50wt.%; metagabbro: 43.71wt.%; amphibolite: 50.24wt.%; garnet-bearing biotite: 63.73wt.%), and MgO (charnockite suite: 0.89–5.01wt.%; metagabbro: 3.99wt.%; amphibolite: 6.23wt.%; garnet-bearing biotite: 2.08wt.%). The composition of the felsic units straddle from diorite through syeno-diorite to granite with both alkalic and subalkalic affinity, with dominantly magnesian composition and arc-related features. Their immobile trace element relationships suggest calc-alkaline affinity. They show positive Pb, Ba, La, Nd, and Gd and negative Nb, Ta, Sr, Th and Ti anomalies with slightly negative anomalies of Ce and Y, attesting to arc-related features. In tectonic classification diagrams, the rocks plot in the VAG+syn-COLG field or the VAG area suggesting subduction-related origin.The dominant population of zircons in all these rocks displays magmatic crystallization features including high Th/U values with core-rims textures indicating subsequent thermal events. The zircon U–Pb data yield upper intercept ages of 2587±10Ma to 2543±17Ma and 207Pb/206Pb mean ages of 2578±7.3Ma to 2536±8Ma for the charnockite suite, marking the timing of emplacement of the arc magmas. The overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207Pb/206Pb ages between 2533Ma to 2490Ma. Zircons in the metagabbro preserve upper intercept ages of 2556±20Ma representing the crystallization age of this rock. The younger ages of 2449±58Ma (upper intercept age) and 1845±25Ma (207Pb/206Pb spot age) are interpreted to represent subsequent multiple thermal events in this area. Zircons in the amphibolite preserve the 207Pb/206Pb mean age of 2539±9Ma, representing the crystallization age of this rock. The garnet-bearing biotite gneiss shows an upper intercept age of 2562±10Ma (MSWD=0.66; N=36) and the 207Pb/206Pb mean age of 2561±9Ma (MSWD=0.63; N=33) which is taken to represent the crystallization age of this rock. Some inherited zircons are also identified with 207Pb/206Pb ages of 2664±26Ma and 2628±26Ma. Zircon Lu–Hf data show dominantly positive εHf(t) values and combined with crustal residence ages, the results suggest Mesoarchean to Neoarchean juvenile crust formation in the NCC. We interpret the data presented here to represent a phase of major late Neoarchaean arc magmatism along the western margin of the Jiaoliao Block related to the birth of microcontinental nuclei within the NCC. Our data suggest that the Western and Eastern Blocks might not have existed as discrete crustal blocks, and that the construction of the NCC is a result of the assembly of several microblocks or terranes at the end of Archaean. Similar Archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early Earth.

A review of the inferred geodynamic evolution of the Dharwar craton over the ca. 3.5–2.5 Ga period, and possible implications for global tectonics

The geological history and evolution of the Dharwar craton from ca. 3.5–2.5 Ga is reviewed and briefly compared with a second craton, Kaapvaal, to allow some speculation on the nature of global tectonic regimes in this period. The Dharwar craton is divided into western (WDC) and eastern (EDC) parts (separated possibly by the Closepet Granite Batholith), based on lithological differences and inferred metamorphic and magmatic genetic events. A tentative evolution of the WDC encompasses an early, ca. 3.5 Ga protocrust possibly forming the basement to the ca. 3.35–3.2 Ga Sargur Group greenstone belts. The latter are interpreted as having formed through accretion of plume-related ocean plateaux. The approximately coeval Peninsular Gneiss Complex (PGC) was possibly sourced from beneath plateau remnants, and resulted in high-grade metamorphism of Sargur Group belts at ca. 3.13–2.96 Ga. At about 2.9–2.6 Ga, the Dharwar Supergroup formed, comprising lower Bababudan (largely braided fluvial and subaerial volcanic deposits) and upper Chitradurga (marine mixed clastic and chemical sedimentary rocks and subaqueous volcanics) groups. This supergroup is preserved in younger greenstone belts with two distinct magmatic events, at 2.7–2.6 and 2.58–2.54 Ga, the latter approximately coincident with ca. 2.6–2.5 Ga granitic magmatism which essentially completed cratonization in the WDC. The EDC comprises 2.7–2.55 Ga tonalite–trondhjemite–granodiorite (TTG) gneisses and migmatites, approximately coeval greenstone belts (dominated by volcanic lithologies), with minor inferred remnants of ca. 3.38–3.0 Ga crust, and voluminous 2.56–2.5 Ga granitoid intrusions (including the Closepet Batholith). An east-to-west accretion of EDC island arcs (or of an assembled arc – granitic terrane) onto the WDC is debated, with a postulate that the Closepet Granite accreted earlier onto the WDC as part of a “central Dharwar” terrane. A final voluminous granitic cratonization event is envisaged to have affected the entire, assembled Dharwar craton at ca. 2.5 Ga. When Dharwar evolution is compared with that of Kaapvaal, while possibly global magmatic events and freeboard–eustatic changes at ca. 2.7–2.5 Ga may be identified on both, the much earlier cratonization (by ca. 3.1 Ga) of Kaapvaal contrasts strongly with the ca. 2.5 Ga stabilization of Dharwar. From comparing only two cratons, it appears that genetic and chronologic relationships between mantle thermal and plate tectonic processes were complex on the Archaean Earth. The sizes of the Kaapvaal and Dharwar cratons might have been too limited yet to support effective thermal blanketing and thus accommodate Wilson Cycle onset. However, tectonically driven accretion and amalgamation appear to have predominated on both evolving cratons.

Archaean drips

The Archaean Earth was much hotter than today. Numerical modelling shows that the base of thickened crust that formed at the time would have been so dense that it dripped back into the mantle.

Delamination and recycling of Archaean crust caused by gravitational instabilities

The volume of Archaean crust preserved at Earth’s surface today is low. Thermodynamic calculations and geodynamic modelling show that the thick, primary crust that would have formed on a much hotter Archaean Earth was denser than the underlying mantle, and would have therefore been recycled back into the mantle as drips.

Isotope composition and volume of Earth’s early oceans

Oxygen and hydrogen isotope compositions of Earth's seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen's was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth's oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH(4) and CO(2) concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth.

Volcaniclastic habitats for early life on Earth and Mars: A case study from ∼3.5 Ga-old rocks from the Pilbara, Australia

Within the context of present and future in situ missions to Mars to investigate its habitability and to search for traces of life, we studied the habitability and traces of past life in ∼3.5 Ga-old volcanic sands deposited in littoral environments an analogue to Noachian environments on Mars. The environmental conditions on Noachian Mars (4.1–3.7 Ga) and the Early Archaean (4.0–3.3 Ga) Earth were, in many respects, similar: presence of liquid water, dense CO 2 atmosphere, availability of carbon and bio-essential elements, and availability of energy. For this reason, information contained in Early Archaean terrestrial rocks concerning habitable conditions (on a microbial scale) and traces of past life are of relevance in defining strategies to be used to identify past habitats and past life on Mars. One such example is the 3.446 Ga-old Kitty’s Gap Chert in the Pilbara Craton, NW. Australia. This formation consists of volcanic sediments deposited in a coastal mudflat environment and is thus a relevant analogue for sediments deposited in shallow water environments on Noachian Mars. Two main types of habitat are represented, a volcanic (lithic) habitat and planar stabilized sediment surfaces in sunlit shallow waters. The sediments hosted small (<1 μm in size) microorganisms that formed colonies on volcanic particle surfaces and in pore waters within the volcanic sediments, as well as biofilms on stabilised sediment surfaces. The microorganisms included coccoids, filaments and rare rod-shaped organisms associated with microbial polymer (EPS). The preserved microbial community was apparently dominated by chemotrophic organisms but some locally transported filaments and filamentous mat fragments indicate that possibly photosynthetic mats formed nearby. Both microorganisms and sediments were silicified during very early diagenesis. There are no macroscopic traces of fossilised life in these volcanic sediments and sophisticated instrumentation and specialized sample preparation techniques are required to establish the biogenicity and syngenicity of the traces of past life. The fact that the traces of life are cryptic, and the necessity of using sophisticated instrumentation, reinforces the challenges and difficulties of in situ robotic missions to identify past life on Mars. We therefore recommend the return of samples from Mars to Earth for a definitive search for traces of life.

Phosphate oxygen isotopic evidence for a temperate and biologically active Archaean ocean

Oxygen and silicon isotope compositions of cherts and studies of protein evolution have been interpreted to reflect ocean temperatures of 55-85 degrees C during the early Palaeoarchaean era ( approximately 3.5 billion years ago). A recent study combining oxygen and hydrogen isotope compositions of cherts, however, makes a case for Archaean ocean temperatures being no greater than 40 degrees C (ref. 5). Ocean temperature can also be assessed using the oxygen isotope composition of phosphate. Recent studies show that (18)O:(16)O ratios of dissolved inorganic phosphate (delta(18)O(P)) reflect ambient seawater temperature as well as biological processing that dominates marine phosphorus cycling at low temperature. All forms of life require and concentrate phosphorus, and as a result of biological processing, modern marine phosphates have delta(18)O(P) values typically between 19-26 per thousand (VSMOW), highly evolved from presumed source values of approximately 6-8 per thousand that are characteristic of apatite in igneous rocks and meteorites. Here we report oxygen isotope compositions of phosphates in sediments from the 3.2-3.5-billion-year-old Barberton Greenstone Belt in South Africa. We find that delta(18)O(P) values range from 9.3 per thousand to 19.9 per thousand and include the highest values reported for Archaean rocks. The temperatures calculated from our highest delta(18)O(P) values and assuming equilibrium with sea water with delta(18)O = 0 per thousand (ref. 12) range from 26 degrees C to 35 degrees C. The higher delta(18)O(P) values are similar to those of modern marine phosphate and suggest a well-developed phosphorus cycle and evolved biologic activity on the Archaean Earth.

The sanukitoid series: magmatism at the Archaean–Proterozoic transition

ABSTRACTA specific type of granitoid, referred to as sanukitoid (Shirey &amp; Hanson 1984), was emplaced mainly across the Archaean–Proterozoic transition. The major and trace element composition of sanukitoids is intermediate between typical Archaean TTG and modern arc granitoids. However, among sanukitoids, two groups can be distinguished on the basis of the Ti content of the less differentiated rocks of the suite: high- and low-Ti sanukitoids. Melting experiments and petrogenetic modelling show that they may have formed by either (1) melting of mantle peridotite previously metasomatised by felsic melts of TTG composition, or (2) by reaction between TTG melts and mantle peridotite (assimilation). Rocks of the sanukitoid suite were emplaced at the Archaean–Proterozoic boundary, possibly marking the time when TTG-dominated granitoid magmatism changed to a more modern-style, arc-dominated magmatism. Consequently, the intermediate character of sanukitoids is not only compositional but chronological. The succession of granitoid magmatism with time is integrated in a plate tectonic model where it is linked to the thermal evolution of subduction zones, reflecting the progressive cooling of Earth: (1) the Archaean Earth’s heat production was high enough to allow the production of large amounts of TTG granitoids formed by partial melting of recycled basaltic crust (‘slab melting’); (2) at the end of the Archaean, due to the progressive cooling of the Earth, the extent of slab melting was reduced, resulting in lower melt:rock ratios. In such conditions the slab melts can be strongly contaminated by assimilation of mantle peridotite, thus giving rise to low-Ti sanukitoids. It is also possible that the slab melts were totally consumed in reactions with mantle peridotite, subsequent melting of this ‘melt-metasomatised mantle’ producing the high-Ti sanukitoid magmas; (3) after 2·5 Ga, Earth heat production was too low to allow slab melting, except in relatively rare geodynamic circumstances, and most modern arc magmas are produced by melting of the mantle wedge peridotite metasomatised by fluids from dehydration of the subducted slab. Of course, such changes did not take place exactly at the same time all over the world. The Archaean mechanisms coexisted with new processes over a relatively long time period, even if they were subordinate to the more modern processes.

Adaptations to submarine hydrothermal environments exemplified by the genome of Nautilia profundicola.

Submarine hydrothermal vents are model systems for the Archaean Earth environment, and some sites maintain conditions that may have favored the formation and evolution of cellular life. Vents are typified by rapid fluctuations in temperature and redox potential that impose a strong selective pressure on resident microbial communities. Nautilia profundicola strain Am-H is a moderately thermophilic, deeply-branching Epsilonproteobacterium found free-living at hydrothermal vents and is a member of the microbial mass on the dorsal surface of vent polychaete, Alvinella pompejana. Analysis of the 1.7-Mbp genome of N. profundicola uncovered adaptations to the vent environment—some unique and some shared with other Epsilonproteobacterial genomes. The major findings included: (1) a diverse suite of hydrogenases coupled to a relatively simple electron transport chain, (2) numerous stress response systems, (3) a novel predicted nitrate assimilation pathway with hydroxylamine as a key intermediate, and (4) a gene (rgy) encoding the hallmark protein for hyperthermophilic growth, reverse gyrase. Additional experiments indicated that expression of rgy in strain Am-H was induced over 100-fold with a 20°C increase above the optimal growth temperature of this bacterium and that closely related rgy genes are present and expressed in bacterial communities residing in geographically distinct thermophilic environments. N. profundicola, therefore, is a model Epsilonproteobacterium that contains all the genes necessary for life in the extreme conditions widely believed to reflect those in the Archaean biosphere—anaerobic, sulfur, H2- and CO2-rich, with fluctuating redox potentials and temperatures. In addition, reverse gyrase appears to be an important and common adaptation for mesophiles and moderate thermophiles that inhabit ecological niches characterized by rapid and frequent temperature fluctuations and, as such, can no longer be considered a unique feature of hyperthermophiles.

Carbon microbubbles sequestration: A novel technology for stable underground emplacement of greenhouse gases into wide variety of saline aquifers, fractured rocks and tight reservoirs

Abstract A novel economic leak-free underground injection technology of greenhouse gas—the carbon (CO 2 ) microbubbles sequesrtrationcan bring the deep reduction of greenhouse gas emission into reality around the world. The atomized foams of CO 2 gas, CO 2 supercritical fluid or CO 2 liquid are dispersed deep into tiny pores of wide variety of underground rocks for virtually permanent storage. The gas microbubbles injection may be effective also for the EOR and EGR in tight rocks such as oil shale and gas shale. Combined effect of hardly buoyant carbon microbubbles, heavy carbon dioxide solution and various trapping mechanisms makes the carbon microbubbles sequestration stable and leak-free in wide variety of geology. The carbon microbubbles injection is suitable also to small scale sequestration of greenhouse gases in the coming hydrogen society as well as large scale CO 2 storage from big coal-fired power plants. The dispersion and dilution of CO 2 in large volume of deep groundwater and rocks by scattered relatively small-scale carbon microbubbles injections are an earth-friendly strategy of greenhouse gas sequestration. The flexibility of site selection makes the source-sink matching much easier for the carbon microbubbles sequestration than conventional direct large-scale injection practices. As we can find the suitable site for the storage near of many large sources of carbon dioxide, the carbon microbubbles sequestration is practically energy-saving and cost-effective greenhouse gas reduction method in many regions. The carbon microbubbles injection can produce the reductive geochemical and biological environments in tiny pores of igneous (especially oceanic) rocks and sequestrate CO 2 into carbonates, organics and methane in the similar mechanism to the Early Archaean earth. The autogenous sealing by carbonate trapping and by hydrate trapping provides the leak proof storage of anthropogenic CO 2 in the deep oceanic crust. The carbon microbubbles sequestration (CMS) provides the economig leak-free option of carbon capture and storage (CCS) and a break-through for the prevention of global warming.

Photosynthetic and atmospheric evolution. Introduction.

The evolution of photosynthesis remade the Archaean Earth. Before photosynthesis, the air and oceans were anoxic. Now the air is a biological construction, a fifth of which is free molecular oxygen, and the ocean can sustain animal life even in the depths. The evolution, first of anoxygenic and then