Earth's Early Atmosphere and Surface Environment

141 Pages·2014·8.103 MB·English

by  George H. Shaw

Earth’s Early Atmosphere and Surface Environment
edited by
George H. Shaw
Geology Department
Union College
Schenectady, New York 12308, USA
Special Paper 504
3300 Penrose Place, P.O. Box 9140 Boulder, Colorado 80301-9140, USA
2014
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Copyright © 2014, The Geological Society of America (GSA), Inc. All rights reserved. Copyright
is not claimed on content prepared wholly by U.S. government employees within the scope of their
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Published by The Geological Society of America, Inc.
3300 Penrose Place, P.O. Box 9140, Boulder, Colorado 80301-9140, USA
www.geosociety.org
Printed in U.S.A.
GSA Books Science Editors: Kent Condie and F. Edwin Harvey
Library of Congress Cataloging-in-Publication Data
Earth’s early atmosphere and surface environment / edited by George H. Shaw, Geology Department,
Union College, Schenectady, New York 12308, USA.
pages cm. — (Special paper ; 504)
Includes bibliographical references.
Summary: “This volume explores the range of conditions and compositions that have been proposed
for Earth’s early surface and atmosphere with a collection of papers presented at a 2011 GSA Pardee
Symposium. Each chapter is accompanied by a commentary and followed by a transcript of the ensuing
discussion at the meeting”— Provided by publisher.
ISBN 978-0-8137-2504-8 (pbk.)
1. Earth (Planet)—Origin—Congresses. 2. Atmospheric chemistry—Congresses. 3. Physical
geography—Congresses. I. Shaw, George H., 1945–. II. Geological Society of America. Meeting (2011:
Minneapolis, Minn.) III. Pardee Keynote Symposium (2011 : Minneapolis, Minn.)
QC879.6.E27 2014
551.51′109012—dc23
2014001614
Cover: (Front) The first unequivocal evidence of life on Earth, a 3.5 Ga stromatolite, lies nestled in
a remote hillside in the Australian Pilbara’s North Pole Dome. Photo by Lev Horodyskyj. (Back)
Ferruginous stromatolites from the Biwabik Iron Formation, Minnesota (ca. 1.8 Ga). The stromatolite
columns are approximately 1 cm across. Photo by E. Calvin Alexander Jr. of a sample from the
collections in the Earth Sciences Department, University of Minnesota.
10 9 8 7 6 5 4 3 2 1
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Contents
Introduction—Earth’s early atmosphere and surface environment
George H. Shaw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .v
SHAW
1. Evidence and arguments for methane and ammonia in Earth’s earliest atmosphere and
an organic compound–rich early ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
George H. Shaw
2. How low can you go? Maximum constraints on hydrogen concentrations prior to
the Great Oxidation Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Shawn Domagal-Goldman
3. Discussion of “Evidence and arguments for methane and ammonia in Earth’s earliest
atmosphere and an organic compound–rich early ocean” (Shaw) . . . . . . . . . . . . . . . . . . . . . . . .15
KASTING
4. Atmospheric composition of Hadean–early Archean Earth: The importance of CO . . . . . . . . . .19
James F. Kasting
5. Atmospheric composition of Hadean–early Archean Earth: The importance
of CO: Comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Laura Schaefer and Bruce Fegley Jr.
6. Discussion of “Atmospheric composition of Hadean–early Archean Earth:
The importance of CO” (Kasting) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
ZAHNLE and CATLING
7. Waiting for O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
2
Kevin Zahnle and David Catling
8. Discussion of “Waiting for O” (Zahnle and Catling) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
2
iii
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iv Contents
OHMOTO et al.
9. Oxygen, iron, and sulfur geochemical cycles on early Earth: Paradigms
and contradictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Hiroshi Ohmoto, Yumiko Watanabe, Antonio C. Lasaga, Hiroshi Naraoka, Ian Johnson, Jamie
Brainard, and Andrew Chorney
10. The upside-down biosphere: “Evidence for the partially oxygenated oceans during
the Archean Eon” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
Shawn Domagal-Goldman
11. Discussion of “Oxygen, iron, and sulfur geochemical cycles on early Earth:
Paradigms and contradictions” (Ohmoto et al.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
REVIEW AND CONCLUSIONS
12. Earth’s early atmosphere and surface environments: A review . . . . . . . . . . . . . . . . . . . . . . . . . .105
Martin J. Van Kranendonk
13. Concluding comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
George H. Shaw
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The Geological Society of America
Special Paper 504
2014
Introduction: Earth’s early atmosphere and
surface environment
Investigations of the chemical state of Earth’s early surface and atmosphere have been guided by geo-
logical evidence, cosmochemical analysis, and comparisons to other terrestrial bodies. A Pardee Symposium
was held at the Geological Society of America Annual Meeting in Minneapolis, Minnesota, on 12 October
2011 with the goal of covering the broadest possible range of ideas that had then been developed addressing
this important, if obscure, period in Earth’s history.
The symposium provided for the presentation and discussion of several, often contradictory, models
for the early Earth. The emphasis was on the later Hadean (post–moon-forming impact) to the late Archean
(Great Oxidation Event), that is, from about 4.3 Ga to 2.1 Ga. The symposium used an unusual format with
the intention of stimulating the maximum amount of discussion of the various views of the nature of Earth’s
early environment. There were four invited papers, with one hour devoted to each topic. The presenters
were asked to submit in advance a written paper of about 3000 words. Each paper was then sent to a “com-
mentator” who prepared a statement of about 1000–1500 words, which was sent back to the presenter.1 The
commentary was not intended or expected to be (solely) a critique of the original paper, but rather to include
additional thoughts based on the content of the paper, in order to further stimulate discussion. At the meeting,
each presenter delivered the paper as originally conceived, not in response to the commentary, in about 25
minutes. The commentator then delivered the commentary in about 10 minutes, followed by a brief response
from the presenter if desired. The remainder of the time was available for discussion. A recording was made
of the entire session in order to prepare a transcript of the discussion. In most cases it was possible to identify
those who made comments or asked questions at the meeting, and they are so indicated in the discussion sec-
tions. Very minor edits and changes for clarity have been made to the discussion segments.
This volume is the tangible result of the symposium. It incorporates the presentations, commentaries,
and discussions in the order presented at the meeting. The review process for the presentations resulted in
some modifi cations to the various texts, but the goal was to preserve, as much as possible, the fl avor of the
symposium. In addition, the inevitable passage of time for preparation of the volume led to some additional
text and references from the past couple years. I believe I have been reasonably true to the essence of the
symposium even with these modifi cations, and they have undoubtedly resulted in improvements to the vari-
ous texts.
With the hope of further increasing the value of this volume, I also commissioned an audience partici-
pant to prepare a paper covering the symposium topic as a whole and summarizing, to the extent possible, the
current state of the fi eld (at least from his viewpoint). One of the goals was to demonstrate a somewhat novel
session format that might be used in the future, and this volume provides a record that might be useful for
someone contemplating this. The success of this effort can perhaps best be suggested by the comment of one
audience participant. After the session, he described his skepticism upon being informed at the beginning, of
the format to be used. He then stated that he felt it was one of the best sessions at the meeting. It should be
clear that this format is probably not amenable to all topics, and may be best suited for those where there is a
1Although the paper by K. Zahnle and D. Catling (Chapter 7) was sent to a commentator, the commentator withdrew at a point in
time too late to obtain a replacement.
Shaw, G.H., 2014, Introduction: Earth’s early atmosphere and surface environment, in Shaw, G.H., ed., Earth’s Early Atmosphere
and Surface Environment: Geological Society of America Special Paper 504, p. v–vi, doi:10.1130/2014.2504(00). For permission to
copy, contact [email protected]. © 2014 The Geological Society of America. All rights reserved.
v
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by guest
on 23 April 2020
vi G.H. Shaw
broad range of views in a focused area, with some degree of controversy implicit in the range. It is our hope
that this effort could be the stimulus for someone to try this again at a future GSA meeting.
As for the substance of the topic discussed, it is clear that an extremely broad range of viewpoints is
held by geologists, geochemists, atmospheric chemists, climate scientists, and various others, as informed by
their own perspectives and the data they feel are most critical to discussion. In some cases, there are disparate
inferences and conclusions drawn from more or less the same basic data. While this may seem surprising,
it is, perhaps, a consequence of the nature of such an ancient and often skimpy geologic record. Although
it is unlikely that all (if any) of the views presented can be correct, there appears at least some possibility
that some (variable) fraction of each may have some validity in forming a picture of an important period of
Earth’s history, one in which it is highly probable that life began its long journey. It is our hope that the dis-
cussions presented herein will help in the development of a self-consistent model of the early Earth.
The underlying theme of the symposium centers on the question of the oxidation state of the atmo-
sphere, and by extension, the general surface environment. The sequence of presentations was chosen to
proceed from consideration of a highly reduced initial surface (G.H. Shaw, Chapter 1), through what is seem-
ingly the generally accepted view of a more or less neutral (in the sense of oxidation state) N-CO (w/CO?)
2 2
atmosphere (J.F. Kasting, Chapter 4), and the processes by which it ultimately became strongly oxidizing and
with free O (K. Zahnle and D. Catling, Chapter 7), to the rather controversial view that free oxygen has been
2
present from very early (perhaps since 3.5 Ga) in Earth’s history (H. Ohmoto et al., Chapter 9). This scheme
to some extent follows the historical development of ideas concerning the atmosphere, but also “bookends”
the more conventional view that N-CO “defi nes” the chemical state of the atmosphere and surface, with
2 2
more radical views on both the more reducing and oxidizing ends of the spectrum. The student of Earth’s
early atmosphere and/or surface will fi nd here the widest range of thought available on this aspect of a critical
and extensive part of Earth’s history
I would like to thank GSA and the Pardee Symposia organizers for sponsoring this symposium, allowing
us to test a novel (for us) format. I would also like to thank all of the participants for their thoughtful contribu-
tions, and the symposium attendees for their energetic discussions. Robert Pepin was gracious enough to be a
co-convener and his participation before, during, and after the symposium is much appreciated.
George H. Shaw
Geology Department, Union College, Schenectady, New York 12308, USA
[email protected]
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by guest
on 23 April 2020
The Geological Society of America
Special Paper 504
2014
Introduction: Earth’s early atmosphere and
surface environment
Investigations of the chemical state of Earth’s early surface and atmosphere have been guided by geo-
logical evidence, cosmochemical analysis, and comparisons to other terrestrial bodies. A Pardee Symposium
was held at the Geological Society of America Annual Meeting in Minneapolis, Minnesota, on 12 October
2011 with the goal of covering the broadest possible range of ideas that had then been developed addressing
this important, if obscure, period in Earth’s history.
The symposium provided for the presentation and discussion of several, often contradictory, models
for the early Earth. The emphasis was on the later Hadean (post–moon-forming impact) to the late Archean
(Great Oxidation Event), that is, from about 4.3 Ga to 2.1 Ga. The symposium used an unusual format with
the intention of stimulating the maximum amount of discussion of the various views of the nature of Earth’s
early environment. There were four invited papers, with one hour devoted to each topic. The presenters
were asked to submit in advance a written paper of about 3000 words. Each paper was then sent to a “com-
mentator” who prepared a statement of about 1000–1500 words, which was sent back to the presenter.1 The
commentary was not intended or expected to be (solely) a critique of the original paper, but rather to include
additional thoughts based on the content of the paper, in order to further stimulate discussion. At the meeting,
each presenter delivered the paper as originally conceived, not in response to the commentary, in about 25
minutes. The commentator then delivered the commentary in about 10 minutes, followed by a brief response
from the presenter if desired. The remainder of the time was available for discussion. A recording was made
of the entire session in order to prepare a transcript of the discussion. In most cases it was possible to identify
those who made comments or asked questions at the meeting, and they are so indicated in the discussion sec-
tions. Very minor edits and changes for clarity have been made to the discussion segments.
This volume is the tangible result of the symposium. It incorporates the presentations, commentaries,
and discussions in the order presented at the meeting. The review process for the presentations resulted in
some modifi cations to the various texts, but the goal was to preserve, as much as possible, the fl avor of the
symposium. In addition, the inevitable passage of time for preparation of the volume led to some additional
text and references from the past couple years. I believe I have been reasonably true to the essence of the
symposium even with these modifi cations, and they have undoubtedly resulted in improvements to the vari-
ous texts.
With the hope of further increasing the value of this volume, I also commissioned an audience partici-
pant to prepare a paper covering the symposium topic as a whole and summarizing, to the extent possible, the
current state of the fi eld (at least from his viewpoint). One of the goals was to demonstrate a somewhat novel
session format that might be used in the future, and this volume provides a record that might be useful for
someone contemplating this. The success of this effort can perhaps best be suggested by the comment of one
audience participant. After the session, he described his skepticism upon being informed at the beginning, of
the format to be used. He then stated that he felt it was one of the best sessions at the meeting. It should be
clear that this format is probably not amenable to all topics, and may be best suited for those where there is a
1Although the paper by K. Zahnle and D. Catling (Chapter 7) was sent to a commentator, the commentator withdrew at a point in
time too late to obtain a replacement.
Shaw, G.H., 2014, Introduction: Earth’s early atmosphere and surface environment, in Shaw, G.H., ed., Earth’s Early Atmosphere
and Surface Environment: Geological Society of America Special Paper 504, p. v–vi, doi:10.1130/2014.2504(00). For permission to
copy, contact [email protected]. © 2014 The Geological Society of America. All rights reserved.
v
Downloaded from https://pubs.geoscienceworld.org/books/chapter-pdf/979796/spe504-v.pdf
by guest
on 23 April 2020
vi G.H. Shaw
broad range of views in a focused area, with some degree of controversy implicit in the range. It is our hope
that this effort could be the stimulus for someone to try this again at a future GSA meeting.
As for the substance of the topic discussed, it is clear that an extremely broad range of viewpoints is
held by geologists, geochemists, atmospheric chemists, climate scientists, and various others, as informed by
their own perspectives and the data they feel are most critical to discussion. In some cases, there are disparate
inferences and conclusions drawn from more or less the same basic data. While this may seem surprising,
it is, perhaps, a consequence of the nature of such an ancient and often skimpy geologic record. Although
it is unlikely that all (if any) of the views presented can be correct, there appears at least some possibility
that some (variable) fraction of each may have some validity in forming a picture of an important period of
Earth’s history, one in which it is highly probable that life began its long journey. It is our hope that the dis-
cussions presented herein will help in the development of a self-consistent model of the early Earth.
The underlying theme of the symposium centers on the question of the oxidation state of the atmo-
sphere, and by extension, the general surface environment. The sequence of presentations was chosen to
proceed from consideration of a highly reduced initial surface (G.H. Shaw, Chapter 1), through what is seem-
ingly the generally accepted view of a more or less neutral (in the sense of oxidation state) N-CO (w/CO?)
2 2
atmosphere (J.F. Kasting, Chapter 4), and the processes by which it ultimately became strongly oxidizing and
with free O (K. Zahnle and D. Catling, Chapter 7), to the rather controversial view that free oxygen has been
2
present from very early (perhaps since 3.5 Ga) in Earth’s history (H. Ohmoto et al., Chapter 9). This scheme
to some extent follows the historical development of ideas concerning the atmosphere, but also “bookends”
the more conventional view that N-CO “defi nes” the chemical state of the atmosphere and surface, with
2 2
more radical views on both the more reducing and oxidizing ends of the spectrum. The student of Earth’s
early atmosphere and/or surface will fi nd here the widest range of thought available on this aspect of a critical
and extensive part of Earth’s history
I would like to thank GSA and the Pardee Symposia organizers for sponsoring this symposium, allowing
us to test a novel (for us) format. I would also like to thank all of the participants for their thoughtful contribu-
tions, and the symposium attendees for their energetic discussions. Robert Pepin was gracious enough to be a
co-convener and his participation before, during, and after the symposium is much appreciated.
George H. Shaw
Geology Department, Union College, Schenectady, New York 12308, USA
[email protected]
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on 23 April 2020
The Geological Society of America
Special Paper 504
2014
Evidence and arguments for methane and ammonia in Earth’s
earliest atmosphere and an organic compound–rich early ocean
George H. Shaw*
Geology Department, Union College, Schenectady, New York 12308, USA
ABSTRACT
The preponderance of geologic evidence does not support carbon dioxide as the
main carbon species degassed from early Earth, nor a carbon dioxide–rich early
atmosphere. In fact, there are several problems that cannot be addressed by assuming
either of these facets of what has become conventional wisdom about the early atmo-
sphere. A careful examination of the conditions that most likely accompanied late
accretion, incorporating the most probable average composition of accreting mate-
rials, suggests an early atmosphere produced by degassing of reduced carbon and
nitrogen species, followed by photochemical processing to yield a surface environ-
ment rich in organic compounds. Recycling of these organics through hydrothermal
and volcanic systems would have maintained a level of reduced gases (photochemi-
cally unstable as they may be) in the early atmosphere for an extended period, accom-
panied by a growing carbon dioxide component derived from mantle magmatism.
Such a model for the early atmosphere is not only consistent with geological data, it
also solves many problems of the early history of Earth.
PROBLEMS WITH THE “STANDARD MODEL” of times present atmospheric concentrations (Kasting, 1993), the
aforementioned problems remain. Solving any one of these prob-
The problems with an early CO-rich atmosphere have been lems does not make the others go away.
2
discussed at length in Shaw (2008a). Briefl y, these include the Earth’s atmosphere is the most changeable element in the
excessive delay in atmospheric oxidation following the advent Earth system, especially over geologic time scales. Earth’s atmo-
of oxygenic photosynthesis (given an enormous supply of pho- sphere was signifi cantly different in the geologic past, with vir-
tosynthetically available CO), diffi culties in producing prebiotic tually no free oxygen before the latest Archean (Cloud, 1968,
2
organics, a lack in the geologic record of the requisite amounts of 1972). The processes involved in atmosphere–ocean–solid Earth
Archean carbonate sediments or their metamorphic equivalents, interactions also operated at signifi cantly different rates during
a lack of intense and pervasive weathering due to atmospheric the Hadean–Archean compared to the present, given the more
acidity/reactivity, and diffi culties with producing the early sedi- energetic state of early Earth. Volcanic exhalation and hydro-
mentary carbon isotope record. In addition, even if (as has been thermal activity were probably greater, and sedimentation was
suggested) the faint young sun paradox might be overcome with mainly in deep water, given the early absence of stable conti-
a CO-rich atmosphere, perhaps at a level hundreds to thousands nental masses. Only by taking into account reasonably probable
2
*[email protected]
Shaw, G.H., 2014, Evidence and arguments for methane and ammonia in Earth’s earliest atmosphere and an organic compound–rich early ocean, in Shaw, G.H.,
ed., Earth’s Early Atmosphere and Surface Environment: Geological Society of America Special Paper 504, p. 1–10, doi:10.1130/2014.2504(01). For permission
to copy, contact [email protected]. © 2014 The Geological Society of America. All rights reserved.
1
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