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ARCHEAN ENVIRONMENTAL STUDIES:THE HABITAT OF EARLY LIFE (ArchEnviron)Standing Committee for Life,Earth and Environmental Sciences (LESC)

RESEARCH NETWORKING PROGRAMME

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The European Science Foundation (ESF) was established in 1974 to create a common European platform forcross-border cooperation in all aspects of scientific research.

With its emphasis on a multidisciplinary and pan-European approach, the Foundation provides the leadershipnecessary to open new frontiers in European science.

Its activities include providing science policy advice (Science Strategy); stimulating co-operation betweenresearchers and organisations to explore new directions (Science Synergy); and the administration of externallyfunded programmes (Science Management). These take place in the following areas: Physical and engineeringsciences; Medical sciences; Life, earth and environmental sciences; Humanities; Social sciences; Polar;Marine; Space; Radio astronomy frequencies; Nuclear physics.

Headquartered in Strasbourg with offices in Brussels, the ESF’s membership comprises 75 national fundingagencies, research performing agencies and academies from 30 European nations.

The Foundation’s independence allows the ESF to objectively represent the priorities of all these members.

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The aim of this Research NetworkingProgramme is to coordinate and encourageresearch on the environment of the early Earthand on the manner in which life emerged andevolved.

The main research topics are:

• Composition and temperature of Archeanatmosphere and oceans;

• The nature of Archean landmasses;

• Interaction between Archean surface watersand the oceanic and continental crust;

• The search for traces of early life.

Our main goal is to obtain a betterunderstanding of the conditions that existed ator near the surface of our planet during the firsttwo billion years of its history. Our approach isbased firmly on the earth sciences but weinteract with complementary programmes suchas molecular biology, genetics and exobiology.

The starting point of the programme is the notionthat conditions at the surface of the Archean Earthmay have been very different from those at present,but in a manner that is as yet poorly understood.

Most probably the Archean sun was less luminous,the mantle was hotter and the atmospherecontained little oxygen, but we do not know howsuch differences influenced the way the Earthfunctioned. Our lack of understanding of theinterplay between solar radiation and atmosphericcomposition means that we are unsure whether theatmosphere and oceans were hotter or colder thanthose of today. Rates of heat production werehigher in the Archean mantle, but because ourunderstanding of mantle convection at that time isrudimentary, we do not know if this differenceresulted in internal temperatures that wereextremely high, or close to those of the present-daymantle.

We know very little about the environments in whichlife may have appeared and later evolved. Twocommonly cited settings for the cradle of life arehydrothermal springs on the ocean floor and tidalflats on the early continents. Our views on the firstare based on studies of black or white smokers onthe modern ocean floor, but their Archeancounterparts may have been very different. Archeanoceanic crust probably was much thicker thanmodern crust and the thermal gradient across thiscrust would have been low: temperatures in theshallow interior of Archean oceanic crust may havebeen lower than those in modern crust, not higheras is commonly assumed. Archean volcanic rockswere more magnesian than their moderncounterparts and Archean ocean water morereducing. How did these differences influenceconditions in Archean hydrothermal springs andwhat was their influence on the appearance andearly evolution of life?

Our knowledge of the second setting is even morerudimentary. The survival of 4.2-4.4 billion year oldzircons for about a billion years on the turbulentsurface of the Archean Earth tells us that felsiccontinents formed very early on and that thesecontinents stayed on the surface throughout theearly Archean. 3.8 Ga sediment rocks in Isua,Greenland tell us that this crust was exposed toweathering and erosion: some of the emergent landin the Archean was very similar to that of today. Butthere may also have been vast “melano” (dark-coloured) continents – emergent volcanic plateauscomposed of mafic to ultramafic volcanic rocks.The best modern analogue of an Archean tidal flatmay be the shores of a tropical Iceland.

It is probable that the volume of ocean water wasgreater than today’s. Was the Archean awaterworld in which only a few small landmasses(mafic or felsic) breached the surface of a globalocean; or did higher mantle temperatures and morevigorous convection produce an extensive networkof emergent mountain ranges along the mid-oceanridges?

The main scientific objective of the programme is toanswer these questions and many others, all crucialto our understanding of the origin and evolution oflife.

Introduction

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Our programme involves scientists and students fromat least 20 different institutions in eight Europeancountries. These include university departments,government research centres and the Geology orNatural Science Museums in three different countries.The list is not exhaustive and we welcome theparticipation of other scientists.

Most of the institutions are in Earth Sciences butthrough the involvement of multidisciplinaryinstitutions such as the Centre of MolecularBiophysics in Orleans, the Darwin Centre forBiogeology in Utrecht and the Centro de BiologíaMolecular in Madrid, and our association with theEuropean Space Agency, we interact with scientistsof other disciplines. We coordinate our activities withprogrammes in other major countries, and withinternational programmes in the fields of Archeanstudies and geomicrobiology.

The principal goal of the programme is to coordinatethe research of those European scientists andstudents who work on the environment of theArchean Earth. We do this by funding exchange visitsbetween participating laboratories of scientists andupper-level research students, and by organisingconferences, workshops and sessions atinternational congresses.

Scope of the Programme

Banded iron formations,

which probably indicate a

change in atmosphere

composition

around 2.5 Ga(photo: N. Arndt)

Impact breccia from theVredefort dome

(photo: C. Koeberl)

Archean pillow lava,

Abitibi greenstone belt,

Canada(photo: N. Arndt)

The research activities of the proposed programmecan be grouped into four main projects.

Project 1: Composition and Temperature ofArchean Atmosphere and Oceans

The question of how the composition, andparticularly the redox state, of the atmosphere andoceans changed during the first 3 billion years ofEarth history has occupied geologists for the pastfour decades. Lively debate continues between twofirmly entrenched schools, one that argues that theatmosphere was relatively reducing for the periodfrom 4.5 Ga up to about 2.5 Ga, the other thatproposes that the change to oxidizingcompositions similar to those of the presentatmosphere happened before 4.0 Ga. Diversearguments are used to defend the opposing pointsof view: geological features that record conditionsduring the deposition of sediments of formation orsoils are particularly important, yet in each casequestions remain as to whether the inferredconditions reflect only a local environment or that ofthe atmosphere/hydrosphere as a whole. Otherapproaches use geochemical data and depend onissues such as the interpretation of mass-independent fractionation of stable isotopes.

Project 2: Nature of Archean Landmasses

Geological and geochemical investigations in rarelocalities where subaerial Archean rocks are knownconstrain the physico-chemical conditions and thetopography of the land surface. The nature ofweathering and erosion, the types of sedimentsthat resulted from this erosion, the fluxes from landto sea may have been radically different for the twotypes of land surface that might have existed in theArchean. At one extreme the “continents” of mafic-ultramafic rock were composed of easily alteredrocks but had subdued relief that mitigated the rateof mechanical erosion. At the other are granitoidcontinents with compositions similar to moderncontinents. However, because of highertemperatures in the mantle and crust, due to higherconcentrations of heat-producing isotopes, themountain ranges may have been lower and thetopography more subdued. How would theselandmasses have reacted to erosion under themore aggressive Archean atmosphere? What typesof sediments were deposited around the edges ofthe early supracrustal masses? What is the origin ofthe silicification that affects such a high proportionof Archean sedimentary and volcanic rocks? Doesthe silicification indicate that hydrothermalcirculation, both within the oceanic crust and onland, was much more common than now? How didthe closer Moon influence tides and their effects onsedimentary structures? How deep was the usualwave-base?

Project 3: Impact of Impacts

How was the Earth affected by meteorite impacts?The lunar impact record indicates that largeimpacts were much more frequent in the Archean,more specifically prior to 3.9 Ga, than at later times.Such frequent and large impact events may havebeen an important factor in the processes thatdetermined the conditions of early life. Largeimpacts are thought to have had a devastatingeffect on life in the more recent history of Earth,such as the KT extinction event. However, in theArchean, meteorite impacts may have influencedthe origin and the habitat of early life. Pre-bioticmolecules, such as amino acids and polycyclicaromatic hydrocarbons, are abundant in space,and meteorites and comets could perhaps haveplayed an important role in providing the necessaryingredients for life on Earth. The energy of theimpact and brecciation of target rocks in the craterresults in extensive hydrothermal systems thatcould provide an ideal habitat for early life.

Project 4:Interaction between Archean Seawater and theOceanic Crust

The goal of this project is to establish the physicaland chemical characteristics of oceanichydrothermal systems in the Archean. Morespecifically, we would aim to establish the size,geometry, and flow rates of the hydrothermal cellsand the changing temperature and chemicalcompositions (Eh, pH, contents of major and traceelements) of the fluids that moved through thesystem. Particular attention will be paid to thechanges in composition that took place as thefluids flowed out of the crust and mixed withArchean seawater.As with the other projects, we will cooperate closelywith groups working on modern hydrothermalsystems on land and in the ocean basins.

Project 5:The Search for Traces of Early Life

A fundamental requirement for life is a steadysource of energy commensurate with therequirements of metabolism. The materials andmodules required for emerging life must also bedelivered at the same time and in the same place.The energy must be sufficient to drive the first cells(e.g. to drive pyrophosphate formation) but not ofsuch power to destroy them. The next fundamentalquestion relates to the formation of RNA, DNA,other polymerised organic molecules and cross-catalytic self-replicating systems. In other words,how could sufficient and sustained concentrationsof the building blocks of life be achieved in aprebiotic world?

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Objectives

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We focus our research on three key field areaschosen using the following criteria: (a) they are theoldest regions in which the geological and tectonicnature of the rock formations can be interpreted inan unambiguous manner; (b) they are regionswhere European geologists have been particularlyactive during the past decade and in which firmresearch collaboration has been established withlocal geologists; (c) they are regions that arepolitically stable and readily accessible.

The Pilbara Belt in Western Australia. This 3.0-3.5Ga region, together with the Barberton belt inSouth Africa, contains the oldest known well-preserved sequences of volcanic and sedimentaryrocks. It is the site of numerous investigations ofthe habitat of early life and the source of some ofmost exciting discoveries in the field. Teams ofDutch, French and British geologists have workedextensively in the region and have established firmresearch contacts not only with Australiangeologists, but also with teams from the USA andJapan who are also very active in the region.

The Barberton Belt in South Africa. This region hasreceived rather less attention by research groups inthe past decade but contains many sequences thatare spectacularly well preserved. It also hasprovided extremely valuable information on theenvironment at the surface of the Archean Earthand has yielded some of the best evidence for theexistence and nature of early life. Cooperativeresearch programmes are well establishedbetween European and South African scientists.

The Abitibi Belt in Canada. Although this belt isconsiderably younger than Pilbara and Barberton, ithas been chosen because the geological setting ofthe rocks is better understood than any otherArchean region. Thanks to concerted and ongoinggeological, geochronological, geochemical andgeophysical studies, mainly by Canadiangeologists, and the remarkable preservation inmany parts of the belt, the conditions ofsedimentation and volcanism, and the entiretectonic evolution of the belt are well constrained.For example, only in this belt can island arcsequences be unambiguously be distinguishedfrom rocks deposited in mid-ocean settings.Investigations in the Abitibi belt will thereforeprovide the firmest constraints on the conditions onthe ocean floor and at the surface of the Archeanearth. Again, firm research links have beenestablished with local geologists.

Field Areas Funding

Living stromalites in the laboratory at ETH Zurich(photo: C. Vasconcelos)

Fossil stromalites

from the Barberton Greenstone belt(photo: N. Arndt)

ESF Research Networking Programmes areprincipally funded by the Foundation’s MemberOrganisations on an à la carte basis. ArchEnviron issupported by:

• Forskningsrådet for Natur og Univers (FNU)Natural Science Research Council, Denmark

• Centre National de la Recherche Scientifique(CNRS)National Centre for Scientific Research, France

• Deutsche Forschungsgemeinschaft (DFG)German Research Foundation, Germany

• Nederlandse Organisatie voor WetenschappelijkOnderzoek (NWO)Netherlands Organisation for Scientific Research,Netherlands

• Consejo Superior de Investigaciones Científicas(CSIC)Council for Scientific Research, Spain

• Ministerio de Educación y Ciencia (MEC)Ministry of Education and Science, Spain

• VetenskapsrådetSwedish Research Council, Sweden

• Schweizerischer Nationalfonds (SNF)Swiss National Science Foundation, Switzerland

• Natural Environment Research Council (NERC),United Kingdom

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Nicholas Arndt (Chair)Laboratoire de Géodynamique desChaînes Alpines 1381 rue de la Piscine 38401 St Martin d’HèresFranceTel: +33 4 76635931 Email: arndt@ujf-grenoble.fr

Ricardo AmilsUniversidad Autonoma de Madrid Centro de Biologia Molecular del CSIC Campus UAM28049 MadridSpainTel: +34 91 497 8078 Email: ramils@cbm.uam.es

David BanksSchool of Earth and EnvironmentUniversity of LeedsWoodhouse LaneLeeds LS2 9JTUnited KingdomTel: +44 113 343 5244Email: D.Banks@earth.leeds.ac.uk

Ulrich RillerHumboldt-Universität zu Berlin Museum für Naturkunde Invalidenstrasse 43 10115 BerlinGermanyTel: +49 30 2093 8573Email:ulrich.riller@museum.hu-berlin.de

Minik RosingGeologisk Museum Oster Voldgade 5-7 1350 Copenhagen KDenmarkTel: +45 3532 2368Email: minik@savik.geomus.ku.dk

Fons StamsWageningen UniversityLaboratory of MicrobiologyPO Box 8033Hesselink van Suchtelenweg 4 6700 EJ Wageningen NetherlandsTel: +31 317 483101Email: fons.stas@wur.nl

Crisogno VasconcelosGeological Institute ETH-Zentrum Sonneggstrasse 8092 ZurichSwitzerlandTel: +41 44 632 3673Email:crisogono.vasconcelos@erdw.ethz.ch

Martin WhitehouseSwedish Museum of Natural HistoryNORDSIM Laboratory for IsotopeGeology Box 50 007 Frescativ. 40 104 05 StockholmSwedenTel: +46 8 5195 5169Email: martin.whitehouse@nrm.se

Tanja ZegersPaleomagnetic Laboratory Institute of Earth Sciences Utrecht University Budapestlaan 17 3584 CD UtrechtNetherlandsTel: +31 71 5656585Email: trzegers@rssd.esa.int

ESF Liaison

Bernard AvrilScience

Life, Earth and EnvironmentalSciences Unit (LESC)European Science Foundation 1 quai Lezay-Marnésia BP 90015 67080 Strasbourg cedex FranceEmail: archenviron@esf.org

For the latest information on thisResearch Networking Programmeconsult the ArchEnviron home page:www.esf.org/archenviron

ArchEnviron Steering Committee

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