DOCSLIB.ORG

Penciling in Details of the Hadean Christopher H

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Penciling in Details of the Hadean Christopher H COMMENTARY Penciling in details of the Hadean Christopher H. House1 this new record of early carbon is exciting Department of Geosciences, Penn State Astrobiology Research Center, Pennsylvania State because it provides a new window into the University, University Park, PA 16802 seemingly accessible Hadean Earth. The Hadean graphite provides a new constraint on the carbon isotopic composi- Some truly remarkable graphite is described (3, 4). So far, these zircons and their inclusions tion of reduced carbon likely deposited in byBelletal.inPNAS(1).Graphiteis,of arecurrentlyouronlytangiblerecordofthe sediments at that time. In the upper left course, the same material as found in pencil first half a billion years of Earth history. portion of Fig. 1, an electron micrograph tips or in the anode of lithium ion batteries. Based in part on the extreme age of some of the Hadean zircon is shown along with Graphite is, however, also a very common of these zircon minerals, along with similarly the δ13Cvalueof−24±4‰, as measured material in Earth Science, and is often the old age dates for a Martian meteorite (5), the using an ion microprobe (1). In geochemis- form of carbon found in very old fossils that Planetary Science and Earth Science commu- try, δ13C values are reported relative to an have been subjected to substantial heat. The nities now appreciate that planets form and inorganic carbonate reference, meaning that graphite described in the Bell et al. article cool rather quickly (6). No longer is the this negative value is quite depleted in 13C is remarkable because it is exceptionally old, Hadean just a placeholder on our timelines relative to typical inorganic carbonate dating to the Hadean eon. Officially, the between the formation of the Earth and the rocks. In fact, the value is indistinguishable Hadean is defined as the time period from oldest known rocks. The Hadean Earth is from biological carbon fractionated by mi- the formation of the Earth until 4 billion y represented by tangible samples that appear crobial carbon fixation. During carbon fix- ago. Until recently, this has been a seemingly to have formed in a continental crust setting, ation, enzymes preferentially incorporate 12C, convenient definition, leaving it as the geo- likely above an active subduction zone (7). leaving inorganic carbon enriched in 13C. logical eon without a rock record on Earth. Specifically, Bell et al. (1) describe two sizable Thus, one of the most important geological Over the past quarter century, however, the graphite inclusions within a 4.1 billion-y-old records for understanding the long habitabil- discovery and exploration of detrital zircon zircon from the Jack Hills. This sample im- ity of the Earth is the record of the carbon minerals from the Jack Hills conglomerates plies that a Hadean chunk of organic material isotopic composition of organic material and of Western Australia (2) have provided a new was transported by geological processes (in- inorganic carbonates back through time window into this early time. Jack Hills zir- cluding subduction) to a granitic magma (8, 9). Broadly, this record convincingly cons crystallized in magma chambers at var- chamber, where it was incorporated into the shows the sustained impact of global marine ioustimesasfarbackas4.4billionyago crystalizing minerals. The sheer existence of carbon fixation on preserved sedimentary carbon going back at least 3.5 billion y. Throughout this long history, microbial life in the oceans would have had a δ13Cvalueof Graphite in Mars Highly about −25‰ (Fig. 1), quite distinct from in- 4.1 Ga Zircon Moon -20‰ 13 organic carbon with a δ C value of about -24±4‰ Reducing Highly -20‰ 0‰. This record of life has potentially been Bell et al. (1) Reducing pushed further back to ∼3.9 billion y ago Prebiotic with the discovery of 13C-depleted graphite Soup? in Greenland metasediments (10, 11). This new discovery of 13C-depleted graphite from 4.1 billion y ago potentially pushes biological Typical carbon into the previously uncharted Hadean. Diamonds The implication is that there was a substantial -5‰ Microbes amount of potentially biogenic carbon on the -25‰ Earth 4.1 billion y ago, 200 million y before the next known sedimentary carbon. Extend- Other Diamonds Moderately -25‰ ing the biological carbon cycle further back Reducing based on this graphite inclusion is simple, consistent, and in line with the principle of Fig. 1. Summary of the few carbon isotopic (δ13C) and redox constraints we have for the Earth’s earliest carbon uniformitarianism. Thus, this discovery sug- cycle. In the upper left is the newly reported carbon isotopic value for a graphite inclusion in a 4.1 Ga Hadean zircon gests life was flourishing in our oceans near (−24 ± 4‰). This remarkable graphite provides a new constraint on the global carbon cycle in the Hadean. Also the end of the Hadean, if not earlier. The shown are Precambrian diamonds (bimodal at −5‰ and −25‰) and Early Archean microbial biomass (scattered around −25%). The Hadean zircon hosting the graphite comes from a continental crust setting, shown as thick and dark brown. Typically, continental crust forms in magma chambers above a subducting slab of oceanic crust, shown Author contributions: C.H.H. wrote the paper. here in black. Finally, various measures of redox suggest that the Earth’s present upper mantle is mildly reducing and The author declares no conflict of interest. has been such for >3.8 billion y. (Inset) Similar constrains for magmatic carbon found in lunar rocks (around −20‰) and Martian meteorites (around −20‰). Both the Moon and Mars appear to have highly reducing mantles. (Inset See companion article on page 14518. image adapted from ref. 1.) 1Email: [email protected]. 14410–14411 | PNAS | November 24, 2015 | vol. 112 | no. 47 www.pnas.org/cgi/doi/10.1073/pnas.1519765112 Downloaded by guest on September 23, 2021 13 next clear step will be to test the continuity aspects of the Earth in its final stage of for- reducing and had significant C-depleted COMMENTARY of possible biogenic graphite preservation in mation. The simplest conclusion is that the carbon in its upper mantle. In other zircon. If this does indeed record ancient Earth’suppermantlewassignificantlymore words, the earliest Earth may have looked sedimentary carbon preserved despite a trip reduced in the beginning. Growing evidence like our present Moon. Certainly, during through a magma chamber, then such a re- indicates that magmatic carbon on Mars (17, the Hadean the Earth’s mantle changed to cord in zircon should be recoverable through 18) and the Moon (19) has a carbon isotopic become more oxidizing and to settle on an the subsequent 4 billion y of Earth history. upper mantle isotopic composition similar to This ancient carbon appears to have had a Bell et al. describe two today. In the beginning, however, a prebiotic wild ride, having been in a magma chamber, sizable graphite inclu- soup could have produced substantial sedi- but looking at carbon from extreme geo- sions within a 4.1 mentary carbon, and it is possible that the logical settings is required to understand the carbon was more 13C-depleted than we nor- ’ Earth s carbon cycle. This new isotope mea- billion-y-old zircon from mally consider. Bell et al. (1) cover their bases surement is one more constraint added to a the Jack Hills. by appropriately calling their graphite poten- substantial body of similar research on mate- tially biogenic. Is the graphite they found from rials extruded from deep within the Earth. composition of about −20‰.Thisissig- 13 a prebiotic soup? It is possible and would be For example, the new measurement is similar nificantly more C-depleted than that of equally exciting, but I do not think so given to some mantle diamonds. Fig. 1 includes Earth’s present upper mantle. At present, that the zircon’s crystallization age is over 400 a summary of several decades of carbon iso- the textbook answer is that the Earth and million y after the Earth’s formation. Four- topic measurements of diamonds extruded Mars started out with different carbon from the Earth’s mantle in violent explosive and that the Moon is just weird, poten- hundred million years is a long time. In terms eruptions. Diamonds show that the mantle is tially having been influenced by meteorite of geophysics, it is more time than plate tec- bimodal with respect to carbon isotopes. impacts. tonics took to both assemble and break-up Most diamonds have carbon isotope values A wild alternative suggestion is that the the supercontinent Pangea. However, the clustered at −5‰, but there is another less- bulk of Earth is actually more 13C-depleted Jack Hills zircons extend back to about abundant group of diamonds with carbon than we think, with an average carbon iso- 4.4 billion y ago, roughly 100 million y isotopic values spread around −25‰ (12, topic value around −20‰. For example, the aftertheMoonwasformed.Ifgraphite 13). Based, in part, on this evidence, the man- Earth’s core could contain significant C, continues to be found in more ancient zir- tle is believed to have an isotopic composition resulting in a fractionated mantle (20). In cons, distinguishing between a dense prebi- of −5‰, and the prevailing view is that the any case, I think it is worth considering otic soup and a productive carbon-fixing more 13C-depleted diamonds represent bio- that at its beginning, the Earth was highly biosphere could be a challenge. genic carbon that has been subducted into the mantle (14). In this interpretation, the 13 transition zone diamonds and the Hadean 1 Bell EA, Boehnke P, Harrison TM, Mao WL (2015) Potentially 10 Rosing MT (1999) C-Depleted carbon microparticles in biogenic carbon preserved in a 4.1 billion-year-old zircon.
Load more

Recommended publications
  • The Evolution and Distribution of Life in the Precambrian Eon-Global Perspective and the Indian Record 765
    The evolution and distribution of life in the Precambrian eon-Global perspective and the Indian record 765 The evolution and distribution of life in the Precambrian eon-Global perspective and the Indian record M SHARMA* and Y SHUKLA Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226 007, India *Corresponding author (Email, [email protected]) The discovery of Precambrian microfossils in 1954 opened a new vista of investigations in the fi eld of evolution of life. Although the Precambrian encompasses 87% of the earth’s history, the pace of organismal evolution was quite slow. The life forms as categorised today in the three principal domains viz. the Bacteria, the Archaea and the Eucarya evolved during this period. In this paper, we review the advancements made in the Precambrian palaeontology and its contribution in understanding the evolution of life forms on earth. These studies have enriched the data base on the Precambrian life. Most of the direct evidence includes fossil prokaryotes, protists, advanced algal fossils, acritarchs, and the indirect evidence is represented by the stromatolites, trace fossils and geochemical fossils signatures. The Precambrian fossils are preserved in the form of compressions, impressions, and permineralized and biomineralized remains. [Sharma M and Shukla Y 2009 The evolution and distribution of life in the Precambrian eon-Global perspective and the Indian record; J. Biosci. 34 765–776] DOI 10.1007/s12038-009-0065-8 1. Introduction suggested that all the living forms can be grouped into three principal domains viz. the Bacteria, the Archaea, and The sudden appearance and radiation of both skeletal and the Eucarya (Woese 1987, 2002; Woese et al.
    [Show full text]
  • Geologic History of the Earth 1 the Precambrian
    Geologic History of the Earth 1 algae = very simple plants that Geologists are scientists who study the structure grow in or near the water of rocks and the history of the Earth. By looking at first = in the beginning at and examining layers of rocks and the fossils basic = main, important they contain they are able to tell us what the beginning = start Earth looked like at a certain time in history and billion = a thousand million what kind of plants and animals lived at that breathe = to take air into your lungs and push it out again time. carbon dioxide = gas that is produced when you breathe Scientists think that the Earth was probably formed at the same time as the rest out of our solar system, about 4.6 billion years ago. The solar system may have be- certain = special gun as a cloud of dust, from which the sun and the planets evolved. Small par- complex = something that has ticles crashed into each other to create bigger objects, which then turned into many different parts smaller or larger planets. Our Earth is made up of three basic layers. The cen- consist of = to be made up of tre has a core made of iron and nickel. Around it is a thick layer of rock called contain = have in them the mantle and around that is a thin layer of rock called the crust. core = the hard centre of an object Over 4 billion years ago the Earth was totally different from the planet we live create = make on today.
    [Show full text]
  • The Geologic Time Scale Is the Eon
    Exploring Geologic Time Poster Illustrated Teacher's Guide #35-1145 Paper #35-1146 Laminated Background Geologic Time Scale Basics The history of the Earth covers a vast expanse of time, so scientists divide it into smaller sections that are associ- ated with particular events that have occurred in the past.The approximate time range of each time span is shown on the poster.The largest time span of the geologic time scale is the eon. It is an indefinitely long period of time that contains at least two eras. Geologic time is divided into two eons.The more ancient eon is called the Precambrian, and the more recent is the Phanerozoic. Each eon is subdivided into smaller spans called eras.The Precambrian eon is divided from most ancient into the Hadean era, Archean era, and Proterozoic era. See Figure 1. Precambrian Eon Proterozoic Era 2500 - 550 million years ago Archaean Era 3800 - 2500 million years ago Hadean Era 4600 - 3800 million years ago Figure 1. Eras of the Precambrian Eon Single-celled and simple multicelled organisms first developed during the Precambrian eon. There are many fos- sils from this time because the sea-dwelling creatures were trapped in sediments and preserved. The Phanerozoic eon is subdivided into three eras – the Paleozoic era, Mesozoic era, and Cenozoic era. An era is often divided into several smaller time spans called periods. For example, the Paleozoic era is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous,and Permian periods. Paleozoic Era Permian Period 300 - 250 million years ago Carboniferous Period 350 - 300 million years ago Devonian Period 400 - 350 million years ago Silurian Period 450 - 400 million years ago Ordovician Period 500 - 450 million years ago Cambrian Period 550 - 500 million years ago Figure 2.
    [Show full text]
  • A Fundamental Precambrian–Phanerozoic Shift in Earth's Glacial
    Tectonophysics 375 (2003) 353–385 www.elsevier.com/locate/tecto A fundamental Precambrian–Phanerozoic shift in earth’s glacial style? D.A.D. Evans* Department of Geology and Geophysics, Yale University, P.O. Box 208109, 210 Whitney Avenue, New Haven, CT 06520-8109, USA Received 24 May 2002; received in revised form 25 March 2003; accepted 5 June 2003 Abstract It has recently been found that Neoproterozoic glaciogenic sediments were deposited mainly at low paleolatitudes, in marked qualitative contrast to their Pleistocene counterparts. Several competing models vie for explanation of this unusual paleoclimatic record, most notably the high-obliquity hypothesis and varying degrees of the snowball Earth scenario. The present study quantitatively compiles the global distributions of Miocene–Pleistocene glaciogenic deposits and paleomagnetically derived paleolatitudes for Late Devonian–Permian, Ordovician–Silurian, Neoproterozoic, and Paleoproterozoic glaciogenic rocks. Whereas high depositional latitudes dominate all Phanerozoic ice ages, exclusively low paleolatitudes characterize both of the major Precambrian glacial epochs. Transition between these modes occurred within a 100-My interval, precisely coeval with the Neoproterozoic–Cambrian ‘‘explosion’’ of metazoan diversity. Glaciation is much more common since 750 Ma than in the preceding sedimentary record, an observation that cannot be ascribed merely to preservation. These patterns suggest an overall cooling of Earth’s longterm climate, superimposed by developing regulatory feedbacks
    [Show full text]
  • Eoarchean Crustal Evolution of the Jack Hills Zircon Source and Loss of Hadean Crust
    Available online at www.sciencedirect.com ScienceDirect Geochimica et Cosmochimica Acta 146 (2014) 27–42 www.elsevier.com/locate/gca Eoarchean crustal evolution of the Jack Hills zircon source and loss of Hadean crust Elizabeth A. Bell ⇑, T. Mark Harrison, Issaku E. Kohl, Edward D. Young Dept. of Earth, Planetary, and Space Sciences, UCLA, United States Received 10 March 2014; accepted in revised form 18 September 2014; available online 30 September 2014 Abstract Given the global dearth of Hadean (>4 Ga) rocks, 4.4–4.0 Ga detrital zircons from Jack Hills, Narryer Gneiss Complex (Yilgarn Craton, Western Australia) constitute our best archive of early terrestrial materials. Previous Lu–Hf investigations of these zircons suggested that felsic (low Lu/Hf) crust formation began by 4.4 to 4.5 Ga and continued for several hundred million years with evidence of the least radiogenic Hf component persisting until at least 4 Ga. However, evidence for the involvement of Hadean materials in later crustal evolution is sparse, and even in the detrital Jack Hills zircon population, the most unradiogenic, ancient isotopic signals have not been definitively identified in the younger (<3.9 Ga) rock and zircon record. Here we show Lu–Hf data from <4 Ga Jack Hills detrital zircons that document a significant and previously unknown transition in Yilgarn Craton crustal evolution between 3.9 and 3.7 Ga. The zircon source region evolved largely by internal reworking through the period 4.0–3.8 Ga, and the most ancient and unradiogenic components of the crust are mostly missing from the record after 4 Ga.
    [Show full text]
  • Convective Isolation of Hadean Mantle Reservoirs Through Archean Time
    Convective isolation of Hadean mantle reservoirs through Archean time Jonas Tuscha,1, Carsten Münkera, Eric Hasenstaba, Mike Jansena, Chris S. Mariena, Florian Kurzweila, Martin J. Van Kranendonkb,c, Hugh Smithiesd, Wolfgang Maiere, and Dieter Garbe-Schönbergf aInstitut für Geologie und Mineralogie, Universität zu Köln, 50674 Köln, Germany; bSchool of Biological, Earth and Environmental Sciences, The University of New South Wales, Kensington, NSW 2052, Australia; cAustralian Center for Astrobiology, The University of New South Wales, Kensington, NSW 2052, Australia; dDepartment of Mines, Industry Regulations and Safety, Geological Survey of Western Australia, East Perth, WA 6004, Australia; eSchool of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT, United Kingdom; and fInstitut für Geowissenschaften, Universität zu Kiel, 24118 Kiel, Germany Edited by Richard W. Carlson, Carnegie Institution for Science, Washington, DC, and approved November 18, 2020 (received for review June 19, 2020) Although Earth has a convecting mantle, ancient mantle reservoirs anomalies in Eoarchean rocks was interpreted as evidence that that formed within the first 100 Ma of Earth’s history (Hadean these rocks lacked a late veneer component (5). Conversely, the Eon) appear to have been preserved through geologic time. Evi- presence of some late accreted material is required to explain the dence for this is based on small anomalies of isotopes such as elevated abundances of highly siderophile elements (HSEs) in 182W, 142Nd, and 129Xe that are decay products of short-lived nu- Earth’s modern silicate mantle (9). Notably, some Archean rocks clide systems. Studies of such short-lived isotopes have typically with apparent pre-late veneer like 182W isotope excesses were focused on geological units with a limited age range and therefore shown to display HSE concentrations that are indistinguishable only provide snapshots of regional mantle heterogeneities.
    [Show full text]
  • Geologic Time Lesson Guide Lesson Guide | Description
    Geologic Time Lesson Guide Lesson Guide | Description Instructor: Dr. Michael T. Lewchuk Grade Level: 6 - 12 Subject: Earth & Physical Science Students will investigate the subdivisions of the Geologic Time Scale. Wonder How: Have you ever wondered how scientists and geologists know how old something is? Goal: Students will gather data and use ratios that will help them create a scale model of Geological time using simple materials found at home. Lesson Guide | Lesson Guide Agenda Lesson Guide Agenda: v Vocabulary v Materials List v Geologic Time Scale v Activity Instructions v Challenge! v Additional Resources v Oklahoma Academic Standards Lesson Guide | Vocabulary Eon – An Eon is the fundamental division of time in Geology. The Earth’s 4.6-billion- year history is divided into four Eons: Hadean, Archean, Proterozoic and Phanerozoic. Precambrian Supereon – This is the combination of the Hadean, Archean and Proterozoic Eons. It is subdivided based on the physical properties of the Earth’s surface and atmosphere. Hadean Eon – The Hadean is the oldest Eon. It is generally described as the time when the Earth was so hot that it was all, or mostly all, molten liquid. Archean Eon – The Archean Eon is generally described as the time when solid rock existed on the surface of the Earth, but little or no free oxygen existed in the atmosphere. Proterozoic Eon – The Proterozoic is generally considered the Eon when free oxygen began to appear in the atmosphere. Microscopic life developed during the Proterozoic. Lesson Guide | Vocabulary Phanerozoic Eon – The Phanerozoic Eon is the most recent Eon in geologic history.
    [Show full text]
  • The World Turns Over: Hadean–Archean Crust–Mantle Evolution
    Lithos 189 (2014) 2–15 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Review paper The world turns over: Hadean–Archean crust–mantle evolution W.L. Griffin a,⁎, E.A. Belousova a,C.O'Neilla, Suzanne Y. O'Reilly a,V.Malkovetsa,b,N.J.Pearsona, S. Spetsius a,c,S.A.Wilded a ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC, Dept. Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia b VS Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia c Scientific Investigation Geology Enterprise, ALROSA Co Ltd, Mirny, Russia d ARC Centre of Excellence for Core to Crust Fluid Systems, Dept of Applied Geology, Curtin University, G.P.O. Box U1987, Perth 6845, WA, Australia article info abstract Article history: We integrate an updated worldwide compilation of U/Pb, Hf-isotope and trace-element data on zircon, and Re–Os Received 13 April 2013 model ages on sulfides and alloys in mantle-derived rocks and xenocrysts, to examine patterns of crustal evolution Accepted 19 August 2013 and crust–mantle interaction from 4.5 Ga to 2.4 Ga ago. The data suggest that during the period from 4.5 Ga to ca Available online 3 September 2013 3.4 Ga, Earth's crust was essentially stagnant and dominantly maficincomposition.Zirconcrystallizedmainly from intermediate melts, probably generated both by magmatic differentiation and by impact melting. This quies- Keywords: – Archean cent state was broken by pulses of juvenile magmatic activity at ca 4.2 Ga, 3.8 Ga and 3.3 3.4 Ga, which may Hadean represent mantle overturns or plume episodes.
    [Show full text]
  • Late Precambrian (Adaptive Radiation/Cambrian/Evolution/Paleontology/Predation)
    Proc. Nat. Acad. Sci. USA Vol. 70, No. 5, pp. 1486-1489, May 1973 An Ecological Theory for the Sudden Origin of Multicellular Life in the Late Precambrian (adaptive radiation/Cambrian/evolution/paleontology/predation) STEVEN M. STANLEY Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland 21218 Communicated by Hans P. Eugster, March 16, 1973 ABSTRACT According to modern ecological theory, Eukaryotic organisms arose earlier than 1300 million years high diversity at any trophic level of a community is pos- ago, and perhaps even earlier than 1700 million years ago, sible only under the influence of cropping. Until herbivores evolved, single-celled algae of the Precambrian were re- but were probably haploid and asexual at first. The oldest source-limited, and a small number of species saturated convincing evidence of sexuality comes from spore-like uni- aquatic environments. In the near-absence of vacant cells in the 900 million year-old Bitter Springs fossil flora. niches, life diversified slowly. Because the changes re- The advent of sexuality should have greatly increased genetic quired to produce the first algae-eating heterotrophs were therefore delayed, the entire system was self-limiting. variability and correspondingly increased rates of evolution- When the "heterotroph barrier" was finally crossed in the ary diversification. It is then puzzling that the Bitter Springs late Precambrian, herbivorous and carnivorous protists flora and various other fossil assemblages of similar age are arose almost simultaneously, for no major biological dif- impoverished relative to modern eukaryote assemblages. ferences separate the two groups. These events automati- They have yielded only simple spheroidal unicells, none of cally triggered the formation of a series of self-propagat- ing feedback systems of diversification between adjacent which exhibits features typical of even moderately advanced trophic levels.
    [Show full text]
  • Temporal Variation in Relative Zircon Abundance Throughout Earth History
    Letter Geochemical Perspectives Letters magma crystallisation, crust production, and even crustal composition (Condie et al., 2009; Cawood et al., 2013; Parman, 2015; Lee et al., 2016). However, quantity of zircon is not a direct substitute for quantity of magma or crust. Instead, zircon © 2017 European Association of Geochemistry abundance in the igneous record is a function of magma composition, which is both spatially and temporally heterogeneous. Moreover, due to the high closure temperatures of the U-Th/Pb and U-series systems, ages from these geochro- Temporal variation in relative zircon nometers exclusively date zircon crystallisation (Schoene, 2014), which need not abundance throughout Earth history coincide with the crystallisation of other silicate minerals. The temperature Tsat at which zircon saturates in an igneous magma can C.B. Keller1,2,3*, P. Boehnke4,5, B. Schoene3 be accurately predicted by an empirical equation of the form Zr a zircon = ln + bM + c T Zr sat melt Abstract doi: 10.7185/geochemlet.1721 where a, b, and c are constants, [Zr] is zirconium concentration, and M is a Zircon is the preeminent chronometer of deep time on Earth, informing models of crustal compositional measure of magma polymerisation defined on a molar basis as growth and providing our only direct window into the Hadean Eon. However, the quantity of zircon crystallised per unit mass of magma is highly variable, complicating interpreta- Na + K + 2 Ca tion of the terrestrial zircon record. Here we combine zircon saturation simulations with a M = dataset of ~52,000 igneous whole rock geochemical analyses to quantify secular variation in Al ∗ Si relative zircon abundance throughout Earth history.
    [Show full text]
  • The Geochronology and Geochemistry of Zircon As Evidence for the Reconcentration of REE in the Triassic Period in the Chungju Area, South Korea
    minerals Article The Geochronology and Geochemistry of Zircon as Evidence for the Reconcentration of REE in the Triassic Period in the Chungju Area, South Korea Sang-Gun No 1,* and Maeng-Eon Park 2 1 Mineral Resources Development Research Center, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea 2 Department of Earth Environmental Science, Pukyong National University, Busan 48513, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-10-9348-7807 Received: 1 November 2019; Accepted: 2 January 2020; Published: 5 January 2020 Abstract: The Chungju rare-earth element (REE) deposit is located in the central part of the Okcheon Metamorphic Belt (OMB) in the Southern Korean Peninsula and research on REE mineralization in the Gyemyeongsan Formation has been continuous since the first report in 1989. The genesis of the REE mineralization that occurred in the Gyemyeongsan Formation has been reported by previous researchers; theories include the fractional crystallization of alkali magma, magmatic hydrothermal alteration, and recurrent mineralization during metamorphism. In the Gyemyeongsan Formation, we discovered an allanite-rich vein that displays the paragenetic relationship of quartz, allanite, and zircon, and we investigated the chemistry and chronology of zircon obtained from this vein. We analyzed the zircon’s chemistry with an electron probe X-ray micro analyzer (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The grain size of the zircon is as large as 50 µm and has an inherited core (up to 15 µm) and micrometer-sized sector zoning (up to several micrometers in size). In a previous study, the zircon ages were not obtained because the grain size was too small to analyze.
    [Show full text]
  • The Geologic Time Scale (Pages 327–329)
    Name Date Class A Trip Through Geologic Time ■ Adapted Reading and Study The Geologic Time Scale (pages 327–329) The Geologic Time Scale (pages 327–328) Key Concept: Because the time span of Earth’s past is so great, geologists use the geologic time scale to show Earth’s history. • Earth has a very long history. Years and centuries are not very helpful for such a long history. So scientists use the geologic time scale for Earth’s history. • The geologic time scale is a record of how Earth and its life forms have changed through time. For example, the scale shows when life first appeared on Earth. • In the geologic time scale, time is divided into bigger blocks than years or centuries. The scale begins when Earth formed 4.6 billion years ago and goes to the present. Answer the following questions. Use your textbook and the ideas above. 1. The record of how Earth and its life forms have changed through time is the . 2. When does the geologic time scale begin? Circle the letter of the correct answer. a. 4 billion years ago b. 4.6 billion years ago c. 544 million years ago 3. Is the following sentence true or false? The geologic time scale divides time into years and centuries. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. 155 Name Date Class A Trip Through Geologic Time ■ Adapted Reading and Study Divisions of Geologic Time (page 329) Key Concept: After Precambrian Time, the basic units of the geologic time scale are eras and periods.
    [Show full text]