The base of the ICS(International Commission on Stratigraphy)Geological Time Scale was ratified in 2022 by defining a new Global Stratigraphic Standard Age(GSSA)for the lower boundary of the Hadean Eon(formerly 4000–...The base of the ICS(International Commission on Stratigraphy)Geological Time Scale was ratified in 2022 by defining a new Global Stratigraphic Standard Age(GSSA)for the lower boundary of the Hadean Eon(formerly 4000–3600 Ma);the age of the Solar System based on the oldest solids,calcium-aluminium inclusions(CAIs),generated in the protoplanetary disk.The formal GSSA for the Hadean base is the oldest reliable,weighted mean Ucorrected Pb–Pb age of 4567.30±0.16 Ma obtained for CAIs in primitive meteorites Allende and Efremovka.This age is supported by the 4568–4567 Ma U-corrected Pb–Pb ages of chondrules in Northwest African meteorites.The boundary sets an upper lifetime for the protoplanetary disk and timing of planet formation.展开更多
Objective The Hadean zircon and rock are critical to deepening our understanding of the developmental history of early Earth, making possible new avenues for the Pre-Archean Eon. However, the Hadean rock on Earth is ...Objective The Hadean zircon and rock are critical to deepening our understanding of the developmental history of early Earth, making possible new avenues for the Pre-Archean Eon. However, the Hadean rock on Earth is only identified in Canada indeed. Comparatively, the Hadean zircon has attracted considerably more attention, as it is widespread and exhibits robust chemical and physical features that make it survive in extreme conditions, thereby providing a method of deciphering the evolution of the early Earth. It should be noted that most of the detrital or the xenocrystic zircons older than 4.0 Ga are found in Western Australia. Hadean zircon occurrences outside Western Australia have been also reported in Canada, west Greenland and China. For the first time,展开更多
The Hadean history of Earth is shrouded in mystery and it is considered that the planet was born dry with no water or atmosphere.The Earth-Moon system had many features in common during the birth stage.Solidification ...The Hadean history of Earth is shrouded in mystery and it is considered that the planet was born dry with no water or atmosphere.The Earth-Moon system had many features in common during the birth stage.Solidification of the dry magma ocean at 4.53 Ga generated primordial continents with komatiite.We speculate that the upper crust was composed of fractionated gabbros and the middle felsic crust by anorthosite at ca.21 km depth boundary,underlain by meta-anorthosite（grossular ＋ kyanite 4 quartz）down to 50-60 km in depth.The thickness of the mafic KREEP basalt in the lower crust,separating it from the underlying upper mantle is not well-constrained and might have been up to ca.100-200 km depending on the degree of fractionation and gravitational stability versus surrounding mantle density.The primordial continents must have been composed of the final residue of dry magma ocean and enriched in several critical elements including Ca,Mg,Fe,Mn,P,K,and Cl which were exposed on the surface of the dry Earth.Around 190 million years after the solidification of the magma ocean, ＂ABEL bombardment＂ delivered volatiles including H_2O,CO_2,N_2 as well as silicate components through the addition of icy asteroids.This event continued for 200 Myr with subordinate bombardments until 3.9 Ga,preparing the Earth for the prebiotic chemical evolution and as the cradle of first life.Due to vigorous convection arising from high mantle potential temperatures,the primordial continents disintegrated and were dragged down to the deep mantle,marking the onset of Hadean plate tectonics.展开更多
The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and ...The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials.展开更多
How and where did life on Earth originate？ To date, various environments have been proposed as plausible sites for the origin of life. However, discussions have focused on a limited stage of chemical evolution, or em...How and where did life on Earth originate？ To date, various environments have been proposed as plausible sites for the origin of life. However, discussions have focused on a limited stage of chemical evolution, or emergence of a specific chemical function of proto-biological systems. It remains unclear what geochemical situations could drive all the stages of chemical evolution, ranging from condensation of simple inorganic compounds to the emergence of self-sustaining systems that were evolvable into modern biological ones. In this review, we summarize reported experimental and theoretical findings for prebiotic chemistry relevant to this topic, including availability of biologically essential elements（N and P） on the Hadean Earth, abiotic synthesis of life＇s building blocks（amino acids, peptides, ribose, nucleobases, fatty acids, nucleotides, and oligonucleotides）, their polymerizations to bio-macromolecules（peptides and oligonucleotides）, and emergence of biological functions of replication and compartmentalization. It is indicated from the overviews that completion of the chemical evolution requires at least eight reaction conditions of（1） reductive gas phase,（2） alkaline pH,（3） freezing temperature,（4）fresh water,（5） dry/dry-wet cycle,（6） coupling with high energy reactions,（7） heating-cooling cycle in water, and（8） extraterrestrial input of life＇s building blocks and reactive nutrients. The necessity of these mutually exclusive conditions clearly indicates that life＇s origin did not occur at a single setting; rather, it required highly diverse and dynamic environments that were connected with each other to allow intratransportation of reaction products and reactants through fluid circulation. Future experimental research that mimics the conditions of the proposed model are expected to provide further constraints on the processes and mechanisms for the origin of life.展开更多
Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth.From these facts,many scientists believe that the primordial continents nev...Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth.From these facts,many scientists believe that the primordial continents never existed during Hadean Earth,and the continental volume has kept increasing.On the other hand,recent studies reported the importance of the primordial continents on the origin of life,implying their existence.In this paper,we discussed the possible process that could explain the loss of the primordial continents with the assumption that they existed in the Hadean.Although depending on the timing of the initiation of plate tectonics and its convection style,subduction erosion,which is observed on the present-day Earth,might have carried the primordial continents into the deep mantle.展开更多
Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the effi...Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine-an automatic zircon separator（AZS）. This is designed particularly for automatic pick-up of100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes：（1） image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray,（2） automatic capturing of the individual zircon grains with microtweezers, and（3） placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical（color） indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e.（1） direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing,（2） high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors（LA-MIC-ICPMS）.With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of 〉150 grains per hour can be achieved with sufficient precision（ca. 0.5%）.We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest（〉4.3 Ga） zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons.展开更多
The mineral schreibersite,（Fe,Ni）_3P,provides a reactive source of phosphorus capable of forming phosphorylated molecules.These molecules may have been an important component of prebiotic chemistry,allowing their bu...The mineral schreibersite,（Fe,Ni）_3P,provides a reactive source of phosphorus capable of forming phosphorylated molecules.These molecules may have been an important component of prebiotic chemistry,allowing their build-up and eventual commencement of autopoiesis.Discussed here are potential geochemical routes to providing schreibersite,as a potentially important prebiotic mineral,to the Hadean Earth.Two routes are identified：delivery of phosphides by meteoritic material and the reduction of phosphates to phosphides by high-temperature,low-redox conditions.About 1-10% of all crustal phosphorus is estimated to have been in schreibersite during the Hadean,making the long-term reaction of this mineral with organic-laden water plausible for many years.Ultimately,such conditions would have been conducive to the formation of life as we know it today.展开更多
文摘The base of the ICS(International Commission on Stratigraphy)Geological Time Scale was ratified in 2022 by defining a new Global Stratigraphic Standard Age(GSSA)for the lower boundary of the Hadean Eon(formerly 4000–3600 Ma);the age of the Solar System based on the oldest solids,calcium-aluminium inclusions(CAIs),generated in the protoplanetary disk.The formal GSSA for the Hadean base is the oldest reliable,weighted mean Ucorrected Pb–Pb age of 4567.30±0.16 Ma obtained for CAIs in primitive meteorites Allende and Efremovka.This age is supported by the 4568–4567 Ma U-corrected Pb–Pb ages of chondrules in Northwest African meteorites.The boundary sets an upper lifetime for the protoplanetary disk and timing of planet formation.
基金financially supported by the National Science Foundation of China (grants No.41430207 and 90914001)the National Key Basic Research Program of China (grant No.2012CB416603)the Science Foundation of China University of Petroleum, Beijing (grant No.2462017YJRC032)
文摘Objective The Hadean zircon and rock are critical to deepening our understanding of the developmental history of early Earth, making possible new avenues for the Pre-Archean Eon. However, the Hadean rock on Earth is only identified in Canada indeed. Comparatively, the Hadean zircon has attracted considerably more attention, as it is widespread and exhibits robust chemical and physical features that make it survive in extreme conditions, thereby providing a method of deciphering the evolution of the early Earth. It should be noted that most of the detrital or the xenocrystic zircons older than 4.0 Ga are found in Western Australia. Hadean zircon occurrences outside Western Australia have been also reported in Canada, west Greenland and China. For the first time,
基金supported by Foreign Expert Funding from China University of Geosciences Beijing
文摘The Hadean history of Earth is shrouded in mystery and it is considered that the planet was born dry with no water or atmosphere.The Earth-Moon system had many features in common during the birth stage.Solidification of the dry magma ocean at 4.53 Ga generated primordial continents with komatiite.We speculate that the upper crust was composed of fractionated gabbros and the middle felsic crust by anorthosite at ca.21 km depth boundary,underlain by meta-anorthosite（grossular ＋ kyanite 4 quartz）down to 50-60 km in depth.The thickness of the mafic KREEP basalt in the lower crust,separating it from the underlying upper mantle is not well-constrained and might have been up to ca.100-200 km depending on the degree of fractionation and gravitational stability versus surrounding mantle density.The primordial continents must have been composed of the final residue of dry magma ocean and enriched in several critical elements including Ca,Mg,Fe,Mn,P,K,and Cl which were exposed on the surface of the dry Earth.Around 190 million years after the solidification of the magma ocean, ＂ABEL bombardment＂ delivered volatiles including H_2O,CO_2,N_2 as well as silicate components through the addition of icy asteroids.This event continued for 200 Myr with subordinate bombardments until 3.9 Ga,preparing the Earth for the prebiotic chemical evolution and as the cradle of first life.Due to vigorous convection arising from high mantle potential temperatures,the primordial continents disintegrated and were dragged down to the deep mantle,marking the onset of Hadean plate tectonics.
基金Financial support from the Ministry of Earth Sci-ences,New Delhi for Excimer 193 nm LA system at CSIR-NGRI MoES/P.O.(Seismo)/1(245)/2014for the project on Singhbhum craton to S.D.,E.V.S.S.K.B.,B.S.and T.V.K(No.MoES/P.O.(Geosci)45/2015+1 种基金GAP-738-28EVB)part of the CSIR-NGRI projects INDEX(PSC0204) and GEOMET
文摘The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials.
基金partly supported by JSPS KAKENHI Grant Nos. 26800276 (Grant-in-Aid for Young Scientists (B)), 16H04074 (Grant-in-Aid for Scientific Research (B)), 16K13906 (Grant-in-Aid for Challenging Exploratory Research), and 26106001 (Grant-in-Aid for Scientific Research on Innovative Areas)
文摘How and where did life on Earth originate？ To date, various environments have been proposed as plausible sites for the origin of life. However, discussions have focused on a limited stage of chemical evolution, or emergence of a specific chemical function of proto-biological systems. It remains unclear what geochemical situations could drive all the stages of chemical evolution, ranging from condensation of simple inorganic compounds to the emergence of self-sustaining systems that were evolvable into modern biological ones. In this review, we summarize reported experimental and theoretical findings for prebiotic chemistry relevant to this topic, including availability of biologically essential elements（N and P） on the Hadean Earth, abiotic synthesis of life＇s building blocks（amino acids, peptides, ribose, nucleobases, fatty acids, nucleotides, and oligonucleotides）, their polymerizations to bio-macromolecules（peptides and oligonucleotides）, and emergence of biological functions of replication and compartmentalization. It is indicated from the overviews that completion of the chemical evolution requires at least eight reaction conditions of（1） reductive gas phase,（2） alkaline pH,（3） freezing temperature,（4）fresh water,（5） dry/dry-wet cycle,（6） coupling with high energy reactions,（7） heating-cooling cycle in water, and（8） extraterrestrial input of life＇s building blocks and reactive nutrients. The necessity of these mutually exclusive conditions clearly indicates that life＇s origin did not occur at a single setting; rather, it required highly diverse and dynamic environments that were connected with each other to allow intratransportation of reaction products and reactants through fluid circulation. Future experimental research that mimics the conditions of the proposed model are expected to provide further constraints on the processes and mechanisms for the origin of life.
基金supported by JSPS KAKENHI(Grand-in-Aid for Scientific Research(S)) Grant No.23224012(Growth of the second continent and mantle)
文摘Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth.From these facts,many scientists believe that the primordial continents never existed during Hadean Earth,and the continental volume has kept increasing.On the other hand,recent studies reported the importance of the primordial continents on the origin of life,implying their existence.In this paper,we discussed the possible process that could explain the loss of the primordial continents with the assumption that they existed in the Hadean.Although depending on the timing of the initiation of plate tectonics and its convection style,subduction erosion,which is observed on the present-day Earth,might have carried the primordial continents into the deep mantle.
基金supported by the Grant-in-Aid from Japan Society of the Promotion for Science (JSPS KAKAENHI New Academic Research No. 26106005)
文摘Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine-an automatic zircon separator（AZS）. This is designed particularly for automatic pick-up of100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes：（1） image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray,（2） automatic capturing of the individual zircon grains with microtweezers, and（3） placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical（color） indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e.（1） direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing,（2） high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors（LA-MIC-ICPMS）.With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of 〉150 grains per hour can be achieved with sufficient precision（ca. 0.5%）.We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest（〉4.3 Ga） zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons.
基金supported by NSF and the NASA Astrobiology Program,under the NSF Center for Chemical Evolution,CHE1504217by National Aeronautics and Space Administration Exobiology grant NNX14AN96G
文摘The mineral schreibersite,（Fe,Ni）_3P,provides a reactive source of phosphorus capable of forming phosphorylated molecules.These molecules may have been an important component of prebiotic chemistry,allowing their build-up and eventual commencement of autopoiesis.Discussed here are potential geochemical routes to providing schreibersite,as a potentially important prebiotic mineral,to the Hadean Earth.Two routes are identified：delivery of phosphides by meteoritic material and the reduction of phosphates to phosphides by high-temperature,low-redox conditions.About 1-10% of all crustal phosphorus is estimated to have been in schreibersite during the Hadean,making the long-term reaction of this mineral with organic-laden water plausible for many years.Ultimately,such conditions would have been conducive to the formation of life as we know it today.
