Archean Environment: the habitat of early life
Mid-term Conference of the Research Networking Program
Archean Environment: the habitat of early life
April 11-12, 2008
Scientific Advisory Committee:
Ricardo Amils (UAM, Madrid)
Goals: The most important physical and chemical conditions when life evolved at the surface of the Archean Earth remain poorly constrained and the driving forces behind the formation and development of the earliest continents are unclear. Extrapolating our knowledge of the modern Earth, including plate tectonics, (bio)geochemical cycles and microbiological ecology back to the first two billion years of Earth history is fraught with difficulty. Life emerged in conditions that may or may not have a modern analogue. This workshop is designed to discuss the latest developments in these fields, within four major themes:
The meeting will be of interest to a wide variety of earth and planetary scientists working in fields related to the early Archean Earth, including geology, geochemistry, geophysics, microbiology, exobiology and geo-chronology.
Report of the Barberton Field Workshop
The Barberton Greenstone Belt contains one of the best-preserved successions of mid-Archean (3.5-3.2 Ga) supracrustal rocks in the world. The volcanic successions provide new insights into volcanic processes, mantle dynamics, and interaction of the oceanic volcanic crust with the hydrosphere and biosphere. Barberton komatiites are unique, both in terms of their age and compositions, yet their complete geochemical characteristics have never been fully documented. The sources of hydrothermal fluids on the ocean floor, driven by circulation of seawater through the volcanic pile, constitute one possible site where life emerged and evolved. Sedimentary sequences provide information about conditions in sedimentary basins: the nature of erosion and sediment transport and deposition, the composition and temperature of Archaean seawater, and a second habitat of early life. Study of tidal sequences provides information about the dynamics of the Earth-Moon system. Finally, investigation of spherule layers and impact debris provide information about the nature and magnitude of meteorite impacts.
The belt, a small, cusp-shaped succession of volcanic and sedimentary rocks invaded on all sides by granitoid plutons is located about 350 km east of Johannesburg. It is world famous for its komatiites, a type of ultramafic lava named after the Komati River which runs through the southern part of the belt and for its thick sequences of sedimentary rocks, which have yielded some of the earliest records of early life. The greenstone sequence has been subdivided into three stratigraphic units: (1) the Onverwacht Group, dominated by ultramafic and mafic volcanic rocks with minor but important sedimentary chert units; (2) the Fig Tree Group, a meta-turbiditic succession made up of greywackes, shales, and cherts; and (3) the Moodies Group, characterized by coarse-grained clastic sedimentary rocks, mainly including sandstones and conglomerates. The protracted, 350 million year long evolution of the region, from initial volcanism and sedimentation through to deformation and granite intrusion, has been used as a model for the formation of the continental crust.
Extensive field-based studies have already provided evidence for the existence as early as 3.5 Ga of a rich microbial ecosystem . Micropaleontological studies show that filamentous and spherical structures reminiscent of modern bacteria, as well as laminated stromatolites representing fossilized microbial mats are widespread but controversial. Stable isotopic data have revealed the likely emergence of diverse groups of prokaryotes including carbon fixing Bacteria and Archaea, methanogens, sulfate reducers and possibly photosynthesizers. Archean sedimentary sequences provide information about conditions at Earth’s surface: the nature of erosion, the transport, deposition and diagenesis of sedimentary material, the thermal history and evolution of sedimentary basins, and thus the overall geodynamic setting on the early Earth.
Controversy surrounds the origin of the ultramafic lavas of the Barberton Belt: many geologists support a model in which the melts form in an unusually hot mantle plume but others advocate melting in cooler conditions in an Archean subduction zone. Resolution of the issue has important implications for our understanding of Archean geodynamics. The rims of basaltic pillows contain micrometer-scale mineralized tubes that provide evidence of submarine microbial activity during the early history of Earth. Black and white smokers on the Archean ocean floor, the exits of hydrothermal fluids that circulated through the basaltic crust represent a possible setting for the emergence and evolution of life.
Sites to be visited will include: (1) The Buck Reef volcanic-sedimentary complex (sedimentary context and habitats of early life, origin of silicification, paleo- land surface processes, role of microorganisms (past and present), hydrothermal cycle, chemistry of the volcano-sedimentary system, properties and composition of Archean seawater and atmosphere); (2) the Theespruit Formation (metamorphic and structural evolution of the oldest rocks in the belt); (3) Komatiites and basalts of the Komati Formation (volcanic settings, geochemistry and dynamics of the Archean mantle, hydrothermal alteration of the ocean crust, properties and composition of Archean seawater and hydrothermal fluids, chemosynthetic development of early life, habitat of micro organisms in the Archean ocean crust) (4) Upper Onverwacht and Fig Tree Groups (hydrothermal sea-floor alteration and Archean seawater composition, Archean mantle processes, traces of early life in carbonaceous cherts, shales and sulfates. Origin of banded iron formations and barites and the evolution of the Archean atmosphere. Evidence for meteorite impacts).
Letter of intent to ICDP (Acrobat pdf file)
Date: 1-2 March 2007
Those intending to attend please contact
Nick Arndt, e-mail firstname.lastname@example.org
Ulrich Riller, e-mail Ulrich.Riller@MUSEUM.HU-Berlin.de
Summary of the project
The project aim is to define conditions at the surface of the Archean Earth through detailed study of drill cores from the Barberton Greenstone Belt, South Africa. The focus will be on the nature of the sedimentary and volcanic rocks that formed the habitat of early terrestrial life. We aim to understand the complex processes of Archean sedimentation and volcanism, and how these interacted at the interface between lithosphere-hydrosphere-atmosphere-biosphere.
The Barberton Greenstone Belt contains one of the best-preserved successions of mid-Archean supracrustal rocks in the world, and is a remarkable natural laboratory where diverse volcanic-sedimentary sequences can be studied in detail. However, despite generally good exposure, nowhere are complete field sections observed, and crucial features such as the contacts of lava flows and continuous successions of critical sedimentary rock sequences, are absent. Only by diamond drilling will we be able to obtain the continuous sections of volcano-sedimentary successions of the type needed for detailed study of the conditions that prevailed at the surface of the Archean Earth.
Two main target areas have been identified for drilling. (1) Sedimentary sequences provide information about the nature of erosion and sediment transport and deposition, the composition and temperature of Archaean seawater, and about the habitat in which life on Earth emerged and evolved. Study of tidal sequences provides information about the dynamics of the Earth-Moon system and investigation of spherule layers and impact debris provide information about the nature and magnitude of meteorite impacts. (2) Komatiite-basalt successions provide new insights into volcanic processes, mantle dynamics, and interaction between oceanic crust and the hydrosphere and biosphere.
Participation in the drilling project and in follow-up studies of recovered drill core will include a broad spectrum of earth scientists. South Africans from at least five universities will handle the local management of the project, assisted by a steering committee containing European and American representatives. Other participants will be drawn from at least seven European countries, as well as from the USA, Australia, China and Japan. International coordination of the project will be assured by ArchEnviron (Archean Environment: the Habitat of Early Life), a research program of the European Science Foundation. Participation and training of students, and in particular those from previously disadvantaged backgrounds will be an important aspect of the project. Komatiites and other rocks in the Archean crust are important depositories of economic minerals, and it is expected that South African mining companies will support the project.
This is the third meeting on this topic. The first was held in Johannesburg on 16th October 2006, the second in San Francisco on 11th December 2006. The minutes of the two meetings are included as separate files.
The main purpose of the meeting at Berlin is to:
|| Logistical information ||
ESF ArchEnviron Programme workshop
April 12-14, Rio Tinto, Spain
Description and objectives
Oceans were most likely the habit of first life on Earth. Although we know from the geological record that water was abundant on the surface of the Earth in Archean, we are only starting to unravel the physical and chemical conditions of oceans in the Archean.
The bathymetry and geological setting of Archean oceans is largely determined by the geodynamical process operating at that time: plate tectonics or a unique Archean geodynamic process ? In addition, the surface of the early Earth may have been determined to a much larger extent by large impact basins than it is today. This has large consequences for the geometry of oceanic basins, as well as the temperature gradient of the oceanic crust.
The composition and temperature distribution of the Archean ocean may have been different from
those of today: temperatures may have been as high as 70 oC, salinities might have been in the
percent rather than the permille range, and redox-sensitive elements, in particular, differed
significantly from those of the modern ocean. The composition depends to a large extent
on the sources (e.g., oceanic crust, seafloor sediments, continental crust) and on the physico-chemical
conditions during weathering and hydrothermal alteration and during mixing of riverine and hydrothermal
waters, respectively, with seawater.
This workshop aims to bring together scientists from diverse fields to integrate the available information on Archean oceans, the theoretical constraints from modeling work on the physical and chemical conditions of Archean oceans, and implications for primitive life.
The workshop will include an excursion to the Rio Tinto area, which is currently regarded as
one of the potential analogues for life on early Earth and on Mars.
Preliminary outline of sessions and schedule
Thursday April 12
PM: Excursion to Rio Tinto area
Friday April 13
PM: Excursion to Rio Tinto area
Application Deadline: 26th February 2007
Scientists interested in contributing to and participating in lively discussions on the nature of Archean oceans and their role as a habitat for early life are encouraged to apply. Potential participants should include a letter of application during the web registration. This letter should include a brief statement of interests, the relevance of the applicant's recent work to the themes of the meeting, the subject of proposed presentation and discussion topics. Those wishing to make an oral or poster presentation should submit an abstract instead of a statement of interests. Interested graduate students are strongly encouraged to apply; partial financial support is available. Invitations will be e-mailed to participants in the first week of March 2007.
The venue will be Hotel Va¡zquez Daaz in Nerva, 90 kms from Seville. A block reservation will be made for participants at the hotel. A bus will be organised to take participants from Seville airport/train station to the hotel. To facilitate logistics, participants are asked to book flights that arrive in Seville before 17.00 on April 11. After the workshop, a bus will bring participants back to Sevilla in the afternoon of Saturday April 14th. ESF will reimburse reasonable travel and accommodation expenses