Did biogeochemical methane cycling regulate the Neoarchean atmosphere?

Lead Research Organisation: University of St Andrews
Department Name: Earth and Environmental Sciences

Abstract

Billions of years ago the young planet Earth was much different from the one we inhabit today, with wildly fluctuating temperatures and an atmosphere filled with toxic gases. Understanding how we got from that inhospitable place to the world of today, dominated by mild climates and large oxygen-based life forms, is a fundamental question in Earth sciences. One important transition occurred approximately 2.5 billion years ago (Ga), called the Great Oxidation Event (GOE), when the oxygen concentrations in Earth's atmosphere first increased from near zero to a fraction of modern levels. A major focus of research in natural science is determining how the Earth system (including life) has acted to produce such monumental changes in the environment; however, exactly how and why the GOE occurred remains a mystery.

Integral to understanding the transition to an oxygenated environment on the early Earth are quantitative estimates of the composition of the ancient atmosphere. These estimates are difficult to make using most geochemical tools, which tend to reflect processes that occurred in the marine environment instead. This study proposes to link the four stable isotopes of sulfur, which directly reflect chemical reactions that occurred in the atmosphere, with numerical models tying these geochemical signatures to atmospheric compositions. An additional set of geochemical analyses will allow us to determine the chemistry of the oceans and how the biosphere was acting at the same time. This study is unique in its combination of these multiple techniques, which we will apply to well-preserved sediments deposited directly before the GOE, to determine how the Earth's atmosphere developed during this time, and how the oceans and biosphere both contributed and responded. Understanding the interactions between the atmosphere, oceans, and life is particularly crucial during this time period, as it represents an Earth system poised at the edge of a major transition in global surface chemistry.

We have performed a preliminary set of similar analyses on ~2.65-2.5 Ga sediments that paint a tantalizing picture of an unusual Earth environment directly before the GOE. These analyses point to an atmosphere that was not only very low in oxygen, but was also periodically dominated by a layer of organic particles (termed "haze") produced at high methane levels, similar to that seen on Saturn's moon Titan. We will expand upon the hypotheses developed from these preliminary analyses and explore their significance for the development of Earth surface chemistry and the evolution of life during this critical period in Earth history.

Planned Impact

Beneficiaries and Relevance of Research:

The beneficiaries of this research beyond the scientific community will be the public sector and the general public, through outreach activities planned by the principal investigators. The question of how life evolved on Earth and how the planet became habitable are topics of great interest to the general public, and are amenable to outreach activities that can easily be presented to a broad audience. In turn, this fosters increased interest in and understanding of environmental science by the broader community. In addition, this research focuses on a critical time period in Earth history that is associated with the run-up to one of the most fundamental changes in the surface of our planet, the Great Oxidation Event. An increased understanding of the interactions between the atmosphere, oceans, and biosphere from this time period is critical to recognizing and interpreting the driving forces and response to major environmental change, and as such is of great interest to the general public as well. This work will additionally strengthen the quality and international recognition of research in England by fostering strong international collaborations with North America (the US), and by promoting interdisciplinary research within the environmental sciences (geochemistry and atmospheric chemistry). The post-doctoral researcher and student will receive a wide range of training that will enhance their skills in fields including analytical geochemistry, biogeochemical cycling, atmospheric and biogeochemical modelling, and Earth system history. These are ideal transferable skills to the employment sector, in either the academic realm or in industry, in consideration of global issues related to environmental changes on Earth.

Engagement with Users and Beneficiaries:

The principal investigators plan to highlight their work to the public wherever possible via public talks, popular science articles, and public outreach activities. The researchers involved in this study all have excellent records in this regard, and will continue to build upon this important area of activity. For example, PI Zerkle has contributed to numerous outreach programs aimed at the general public, including Space Day (at Pennsylvania State University) and Maryland Day (at the University of Maryland), and is planning a public exhibit at the Hancock Great North Museum in Newcastle on Earth surface oxygenation. Co-I Poulton gave a keynote lecture on the oxygenation history of the ocean at the 2009 British Science Festival and has given several other public lectures. Co-I Claire has developed planetarium shows for the Pacific Science Center (Seattle, WA) and is a founding member of Blue Marble Space Institute, which has partnered with NASA to bring the Cheltenham Festival's flagship science communication activity - FameLab - to the United States.

In particular, as part of this project we will host two workshops highlighting research on the Precambrian Earth, as discussed in Academic Beneficiaries above. Each of these workshops will entail a public lecture to be delivered by an international guest speaker (PP Farquhar is confirmed for one of these lectures, see letter of support). We are further committed to advertising our findings through the media and through popular articles. We also propose to highlight major outcomes of this proposal, as they are generated, through press releases at Newcastle University and the University of East Anglia. In addition we will engage with colleagues at these workshops and at international and national scientific meetings and foster future scientific development and additional collaborations.

Publications

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Farquhar J (2013) Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes. in Proceedings of the National Academy of Sciences of the United States of America

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Izon G (2017) Biological regulation of atmospheric chemistry en route to planetary oxygenation. in Proceedings of the National Academy of Sciences of the United States of America

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Mettam C (2017) High-frequency fluctuations in redox conditions during the latest Permian mass extinction in Palaeogeography, Palaeoclimatology, Palaeoecology

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Zahnle K (2013) The rise of oxygen and the hydrogen hourglass in Chemical Geology

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/J022802/1 01/12/2012 31/05/2013 £100,221
NE/J022802/2 Transfer NE/J022802/1 01/10/2013 30/03/2017 £95,411
 
Description We have shown that methane producing microbes so significantly altered atmospheric chemistry during Earth's Archean epoch that it produced an organic haze layer, similar to Saturn's moon Titan. We've produced a novel methodology for how to model/interpret sulfur isotopes in Earth's ancient atmosphere and sediments. In our most recent work, we have detailed conditions in the Earth system that enable hazy atmospheric conditions, and how these tie into the bigger picture of planetary oxidation.
Exploitation Route We are continuing with this discovery research project, in an attempt to understand what the Earth system was like at this time period.
Sectors Other

URL http://phys.org/news/2015-11-early-earth-periodically-hazy.html
 
Description The inital papers have just started to come out, but they are well cited. The new work is being presented at conferences.
First Year Of Impact 2014
 
Title Atmospheric minor sulfur isotopes 
Description We presented a numerical model of atmospheric chemistry which is capable of predicting minor sulfur isotope paterns 
Type Of Material Computer model/algorithm 
Year Produced 2014 
Provided To Others? Yes  
Impact The paper was recently published (in an open source format), and is being utilized by other research groups 
URL http://www.sciencedirect.com/science/article/pii/S0016703714004475
 
Description Colin Mettam to SUERC 
Organisation University of Glasgow
Department NERC SUERC CIAF Cosmogenic Isotope Analysis Facility
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution We sent Colin to Syracuse University in the US to learn a novel technique for nitrogen isotope preparation. In early 2016, Colin went to SUERC to set up the method there.
Collaborator Contribution They will provide technical expertise, parts, labor, as well as isotopic measurements
Impact Funding took much longer to come through than original anticipated, and necessary parts were not ordered by SUERC until early in 2016. Colin went to SUERC in January/February 2016 and built a working cryotrap. Data is forthcoming...
Start Year 2014
 
Description Colin Mettam to Syracuse 
Organisation Syracuse University
Country United States of America 
Sector Academic/University 
PI Contribution PGR student Colin Meetam went to Syracuse university on NERC funds
Collaborator Contribution Syracuse hosted and housed him, provided training on novel isotopic techniques, and did not charge for samples run
Impact Preliminary results were presented on November 5 at the Life and the Planet meeting in London, and at the 2015 Geochemistry research in progress meeting in Leeds.
Start Year 2014