Toby Tyrrell, author of On Gaia, explains how he came to question the Gaia Hypothesis

We interviewed Toby Tyrrell about his new book “On Gaia” last week. This week, we’re proud to link to this article in which he details some of the research that led him to view the Gaia Hypothesis with a critical eye:

Nitrogen is exceptionally abundant in the environment, it makes up 78 per cent of air, as dinitrogen (N2). N2 is also much more plentiful in seawater than other dissolved forms of nitrogen. The problem is that only organisms possessing the enzyme nitrogenase (organisms known as nitrogen-fixers) can actually use N2, and there aren’t very many of them. This is obviously a less than ideal arrangement for most living things. It is also unnecessary. Nitrogen starvation wouldn’t happen if just a small fraction of the nitrogen locked up in N2 was available in other forms that can be used by all organisms; yet biological processes taking place in the sea keep nearly all that nitrogen as N2. If you think about what is best for life on Earth and what that life can theoretically accomplish, nitrogen starvation is wholly preventable.

This realisation led me to wonder what other aspects of the Earth environment might be less than perfect for life. What about temperature? We know that ice forming inside cells causes them to burst and that icy landscapes, although exquisite to the eye, are relatively devoid of life. We can also see that ice ages – the predominant climate state of the last few million years – are rather unfortunate for life as a whole. Much more land was covered by ice sheets, permafrost and tundra, all biologically impoverished habitats, during the ice ages, while the area of productive shelf seas was only about a quarter of what it is today. Global surveys of fossil pollen, leaves and other plant remains clearly show that vegetation and soil carbon more than doubled when the last ice age came to an end, primarily due to a great increase in the area covered by forests.

Although the cycle of ice ages and interglacials is beyond life’s control, the average temperature of our planet – and hence the coldness of the ice ages – is primarily determined by the amount of CO2 in the atmosphere. As this is potentially under biological control it looks like another example of a less than perfect outcome of the interactions between life on Earth and its environment.

Look further and you find still more examples. The scarcity of light at ground level in rainforests inhibits growth of all but the most shade-tolerant plants. There’s only really enough light for most plants at canopy height, often 20 to 40 metres up, or below temporary gaps in the canopy. The intensity of direct sunlight does not increase the higher you go, so having the bulk of photosynthesis taking place at such heights brings no great advantage to the forest as a whole. Rather the contrary, trees are forced to invest large amounts of resources in building tall enough trunks to have the chance of a place in the sun. This arrangement is hard to understand if you expect the environment to be arranged for biological convenience, but is easily understood as an outcome of plants competing for resources.

Source: “Not Quite Perfect”, Planet Earth Online:


Read a sample chapter from On Gaia: A Critical Investigation of the Relationship between Life and Earth [PDF].

Q&A with Toby Tyrrell, author of “On Gaia”


tyrell_toby_au photo

Toby Tyrrell is professor of Earth system science at the National Oceanography Centre Southampton (University of Southampton). His new book On Gaia: A Critical Investigation of the Relationship between Life and Earth publishes at the end of July.

He kindly answered some questions from our UK Director of Publicity Caroline Priday.

Q: Why did you write this book

A: My aim was to determine whether the Gaia hypothesis is a credible explanation of how life and environment interact on Earth.


Q: What is the Gaia hypothesis?

A: James Lovelock’s Gaia hypothesis, first put forward in the 1970’s, proposes that life has played a critical role in shaping the planetary environment and climate over ~3 bil­lion years, in order to keep it habitable or even optimal for life down through the geological ages. Life has not been merely a passive pas­senger on a fortuitously habitable Earth, it is claimed, but rather has shaped the environment and helped to keep it comfortable.


Q: Why has there been so much interest in the Gaia hypothesis?

A: In part because it suggests answers to some fundamental questions of widespread interest, such as how it is that Earth remained continuously habitable for so long, how did our planet and the life upon it end up the way they are, and how does the Earth system work?


Q: Lots of scientists have considered Gaia before – what is different about this book?

A: Previous books have been mostly reviews of the scientific debates over Gaia, collections of scientific papers, or congratulatory restatements of Gaia by supporters. This book is the first to submit the Gaia hypothesis to detailed sceptical scrutiny, subjecting each of three main arguments put forward in support of Gaia to close analysis, and comparing them to modern evidence collected in the more than 30 years since the Gaia hypothesis was first proposed. It is the first book containing a hard-nosed and thorough examination of the Gaia hypothesis.


Q: What are the three main arguments that have been advanced in support of Gaia?

A: Firstly, that the Earth is very comfortable for life. Secondly, that the presence of life on Earth has profoundly altered the nature of the planetary environment. And thirdly, that the environment has remained fairly stable over geological time.


Q: What is the main conclusion of the book?

A: That the Gaia hypothesis does not “hold up in court”: it is not consistent with modern scientific evidence and understanding and should therefore be rejected.


Q: What are the reasons given for rejecting the Gaia hypothesis?

A: Firstly because there are no facts or phenomena that can be explained only by Gaia (no ‘smoking gun’). Secondly because there is no proven mechanism for Gaia (no accepted reason for why it should emerge out of natural selection). And thirdly because the key lines of argument that Lovelock and others advanced in support of Gaia either give equally strong support to alternative hypotheses or else are mistaken. For instance the planet is not excessively favourable for life: it has been colder than optimal during the ice ages that have occupied the majority of the last few million years, and unnecessary nitrogen starvation is ubiquitous. Its environmental history has not been all that stable: we now have abundant evidence of past environmental instability, from ice age cycles to seawater Mg/Ca variation to Snowball/Slushball Earths.


Q: If life and its environment do not interact in the way suggested by Gaia (life moulding the environment towards its own convenience) then how do they interact?

A: Through ‘coevolution’. Stephen Schneider and Randi Londer put forward the idea of a coevolution between life and its environment: biological processes such as oxygen production by photosynthesis shape the environment, and, clearly, the environment also strongly influences life through evolution of organisms to fit their environments. Coevolution recognises that both affect the other. Unlike Gaia, however, coevolution does not claim any emergent property out of the two-way interaction between life and environment. It is neutral with regards to predictions about the resulting effect on the environment. It does not suggest that the interaction tends to improve living conditions on Earth.


Q: If the Gaia hypothesis is not the reason, then why did the Earth remain habitable for such an enormously long interval of time?

A: This may relate partly to the weak Anthropic Principle, whereby we logically cannot observe any facts that preclude our own existence. So however infrequent it may be in the universe for a planet to remain continuously habitable over billions of years, we happen to be on just such a planet. According to this way of thinking, Earth may just have been lucky, with no sentient observers having evolved on other planets which were not so lucky, i.e. where conditions became sterile at some point. Another possible explanation for extended habitability in the absence of Gaia is a predominantly inorganic thermostat, such as has been suggested for silicate weathering.


Q: Why would people be interested in this book?

A: It considers some of the great questions about the nature of our planet, its history, and how it came to give rise to us. Many fascinating topics are covered, often from little-known corners of the natural world. Examples include: hummingbirds in the High Andes and the similarity of their beaks to the flowers they extract nectar from, the wonderfully-named Walsby’s square archaeon in the Dead Sea, the ever-lasting durability of the waste that coral reefs generate (not everything in nature is recycled), changes in the nature of the saltiness of seawater over geological time, and differences in the way Australian snakes bear young depending on climate (they don’t always lay eggs).


Q: Are there any implications for the current era of global change?

A: Yes, it is suggested that belief in the Gaia hypothesis can lead to excessive complacency about the robustness and resilience of the natural system. Gaia emphasizes stabilising feedbacks and protective mechanisms that keep the environment in check. If Gaia is rejected, however, we are left with a less comforting view of the natural system. Without Gaia it is easier to appreciate that the natural system contains lines of weakness and other susceptibilities. One such line of weakness that has already been demonstrated is the ozone layer depletion by CFC’s. I have argued in the book that there is no over-riding Gaia to protect our planet’s life support system. Maintaining the Earth’s environment is up to us.


Read a sample chapter from On Gaia: A Critical Investigation of the Relationship between Life and Earth [PDF].

[THURSDAY, July 4th] Life and environment: An evaluation of the Gaia Hypothesis by Professor Toby Tyrrell

Life and environment: An evaluation of the Gaia Hypothesis

by Professor Toby Tyrrell

Toby will be signing copies of his book at 6:30pm.

Categories: Lectures & Discussions, Book Signing
Co-sponsor: Natural Environment Research Council (NERC)
Date: Thursday, July 4th, 2013
Time: 6:30pm – 8:30pm. Toby will be signing copies of his book at 6:30pm. The Marine Life Talks are held at 7:30pm. Please arrive no later than 7:15pm.
Venue: The National Oceanography Centre
Address: National Oceanography Centre
University of Southampton Waterfront Campus
European Way
Southampton SO14 3ZH
United Kingdom
Location: Reached via Dock Gate 4 (between Southampton’s Town Quay and Ocean Village).
Cost: Free admission – these talks are open to the public

View this event on the National Oceanography Center website:

In 1972 James Lovelock made an interesting proposal. Life is not solely a pas­senger on a fortuitously habitable Earth, he suggested. Instead, life has been at the controls of the planetary environment, helping to ensure continued habitability over ~3 bil­lion years. In the thirty years or so since he first proposed it, the Gaia hypothesis has intrigued a whole generation of those interested in natural history and planet Earth. Today it is widely but by no means universally credited by scientists. It remains controversial.

Gaia is a fascinating idea, but is it correct? In this talk Toby Tyrrell will attempt to an answer this overall large question by first exploring some smaller questions that relate to the larger one. First Toby will look at cooperative regulation of a shared living space: under what circumstances is this observed to occur in nature? Second he will consider whether the biota has altered the environment on a global scale. Finally Toby will discuss whether the changes to environmental conditions following evolutionary innovations have or have not been broadly favorable for life. He will combine the answers to each of these questions into a wider evaluation of whether the Gaia hypothesis is plausible and consistent with modern evidence and will conclude that it is not. Instead a competing hypothesis, co-evolution of life and environment, will be suggested to be compatible with our modern understanding in a way that Gaia is not.

Toby Tyrrell has long been interested in the dynamics and interactions of life and environment on Earth. Encompassed within that rather large topic, his narrower research interests have included enthusiasms on coccolithophores, the ocean carbon and nutrient cycles and ocean acidification. After an undergraduate degree in Civil Engineering at the University of Southampton he gained an MSc in Artificial Intelligence at the University of Edinburgh and then a PhD from the same institution. He spent two years working on ecological modelling at Plymouth Marine Laboratory. Since then he has been a researcher then lecturer and now professor of Earth system science in the University of Southampton, NOCS.

This talk is linked with publication of a book on the same topic:

Recordings of previous Marine Life Talks can be found on:

The Marine Life Talks are held on the first Thursday of the month at 7.30pm. Please arrive no later than 7:15pm.

Arrangements for wheelchairs must be made in advance. Unless it is possible to descend via the stairs in an emergency, access to upper floors cannot be permitted as lifts are automatically immobilized when the fire alarm is activated.

The National Oceanography Centre is reached via Dock Gate 4 (between Southampton’s Town Quay and Ocean Village).

About Toby Tyrell:

Toby Tyrrell, author of On Gaia: A Critical Investigation of the Relationship between Life and EarthResearch Interests

Specialism: Ocean acidification

How organisms interact with their environments. Ecology of phytoplankton, coccolithophores in particular. Ocean acidification. Ocean biogeochemistry, including during extreme events in Earth’s ancient past such as the E/O and K/T boundaries. Ocean carbon cycle and its effect on future atmospheric CO2 levels. Marine cycles of N, P, C, Si. The control of biogenic element concentrations in the sea as a function of ecological competition between different functional groups of phytoplankton.

PhD Supervision

Zongpei Jiang, Dave Mackay, Claudia Fry, Tingting Shi, Christopher Daniels, Matthew Humphreys.

Primary research group: Ocean Biogeochemistry and Ecosystems

Affiliate research group: Palaeoceanography and Palaeoclimate

Research projects

  • Leader of NOCS Beacon Theme on Ocean Acidification
  • Coordinator of the sea-surface consortium, a major component (>£3m, 10 partner institutions) of the United Kingdom Ocean Acidification Research Programme.


Source Credit For About Toby Tyrrell: University of Southampton

On Gaia:
A Critical Investigation of the Relationship between Life and Earth
Toby Tyrrell

On Gaia: A Critical Investigation of the Relationship between Life and Earth by Toby Tyrrell“A handful of scientists have become crusaders for the Gaia hypothesis, while the rest have dismissed it without a second thought. Toby Tyrrell, on the other hand, is one of the very few scientists to have considered the evidence at length and in detail. In summarizing nearly forty years of arguments for and against the Gaia hypothesis, he has done a great service for anyone who is curious about Gaia, or about this fascinating planet that we all call home.”–James Kirchner, University of California, Berkeley

“Toby Tyrrell unravels the various formulations of Gaia and explains how recent scientific developments bring the hypothesis into question. His criticisms are insightful, profound, and convincing, but fair. On Gaia is wonderfully informative and a pleasure to read.”–Francisco J. Ayala, author of Am I a Monkey?: Six Big Questions about Evolution

“At last, a beautifully written and clear-eyed analysis of the interplay of life and the Earth system. On Gaia provides the understanding for moving forward in the quest for sustainability, and is essential reading if our planet is to remain habitable for humanity.”–Thomas E. Lovejoy, George Mason University

On Gaia makes a wonderful addition to the literature. It is scholarly, well-written, and well-reasoned.”–Simon A. Levin, Princeton University

Dinosaur Embryo Discovered

Stated simply, dinosaurs are cool. Jurassic Park may have given me nightmares once I was old enough to see it, but they are frighteningly majestic.

Paleontologists discovered fossilized dinosaur embryos in China recently making them the oldest preserved organic remains of a  budding dinosaur to date. The embryos are thought to be sauropodomorphs “because they are similar in many ways to intact embryonic skeletons of Massospondylus, a sauropodomorph that Reisz [paleontologist]  unearthed in South Africa in 2005″  according to The new discoveries will help scientists understand better how these dinosaurs grew to their full adult size.

4-11 dinos

Left: Sauropodomorph in egg. Image via the Huffington Post
Right: Adult sauropodomorph. Image via BBC

Unfortunately, it is confirmed that there is no probability that these embryos could result in dinosaur reincarnation.

To learn more about sauropodomorphs, The Princeton Field Guide to Dinosaurs by Gregory S. Paul has an entire chapter devoted to them.

The Princeton Field Guide to Dinosaurs is a must-have for anyone who loves dinosaurs, from the amateur enthusiast to the professional paleontologist.

  • The first authoritative field guide to dinosaurs
  • Covers more than 735 species
  • Beautiful, large-format volume
  • Lavishly illustrated throughout, with more than 600 color and black-and-white drawings and figures, including:
  • More than 130 color life studies, including scenic views
  • Close to 450 skeletal, skull, head, and muscle drawings
  • 8 color paleo-distribution maps
  • Color timeline
  • Describes anatomy, physiology, locomotion, reproduction, and growth of dinosaurs, as well as the origin of birds and the extinction of nonavian dinosaurs

And, while mosquitoes in fossilized amber can’t bring back dinosaurs, The Amber Forest: A Reconstruction of a Vanished World by George Poinar Jr., & Roberta Poinar brings to life the environment in which the dinosaurs lived.

In Jurassic Park, amber fossils provided the key to bringing dinosaurs back to life. Scientists in the movie extracted dinosaur blood from mosquitoes preserved for millions of years in amber–hardened tree resin–and used the blood’s DNA to revive the creatures that terrified audiences around the globe. In this book, George and Roberta Poinar use amber for a similar act of revival–only they bring back an entire ecosystem. The Poinars are world leaders in the study of amber fossils and have spent years examining the uniquely rich supply that has survived from the ancient forests of the Dominican Republic. They draw on their research here to reconstruct in words, drawings, and spectacular color photographs the ecosystem that existed on the island of Hispaniola between fifteen and forty-five million years ago. The result is the most accurate picture scientists have yet produced of any tropical forest of the past.

The specimens examined by the Poinars reflect amber’s extraordinary qualities as a medium for preservation. Millions of years ago, countless plants, invertebrates, and small vertebrates were trapped in the sticky resin that flowed from the trees of ancient forests and, as that resin hardened into translucent, golden amber, they were preserved in almost perfect condition. Samples analyzed and illustrated here include a wide range of insects and plants–many now extinct–as well as such vertebrates as frogs, lizards, birds, and small mammals. There are even frozen scenes of combat: an assassin bug grappling with a stingless bee, for example, and a spider attacking a termite. By examining these plants and animals and comparing them to related forms that exist today, the authors shed new light on the behavior of these organisms as well as the environment and climate in which they lived and died.

The Poinars present richly detailed drawings of how the forests once appeared. They discuss how and when life colonized Hispaniola and what caused some forms to become extinct. Along the way, they describe how amber is formed, how and where it has been preserved, and how it is mined, sold, and occasionally forged for profit today. The book is a beautifully written and produced homage to a remarkable, vanished world.

Eric Heller explains unexplainable booms at Huffington Post

Without precedent or warning, a loud boom sounding like a major piece of artillery frightens your normally quiet neighborhood. Houses shake and dishes rattle. The jolt is singular, percussive — and ominous. Later the TV news reports that the boom was heard over many miles, but nothing exploded. No supersonic aircraft flew by. Someone saw yellow light in the sky.

Residents of New York’s Rockland and Westchester Counties, not far from New York City, experienced this in March 2009. It could have been a rare, beach ball sized meteor that disintegrated before it hit the ground. Meteors are certainly supersonic and have been known to make loud sonic booms. A bounty hunter offered $10,000 for a piece of the meteorite.

But the meteor theory blew up a couple days later. Another loud boom in the same area jolted people awake at 5:15 am. Nanuet resident Keith Wallenstein said of the second boom. “The house was shaking. It sounded like someone had flown an F-16 over the house. If it was thunder, it had to be right on the house. [But] I know a bunch of people who heard it within 3 to 4 or 5 miles away.”

By now you may be thinking the military was up to something after all. They’d be mum about it, wouldn’t they?

Click over to Huffington Post to read the complete explanation.

Eric Heller, a theoretical physicist and chemist specializing in waves of all kinds, explains that while loud sounds like this have troubled people throughout history and are often explained away by mythology and conspiracy, they are usually caused by small, but highly accelerated movements in the ground.

“Oddly, the surface does not need to move very far nor very fast to launch exceedingly loud sound resembling cannon fire or a sonic boom. What it does need is a lot of acceleration. But how can something have huge acceleration, yet not wind up moving very far or very fast?”

Click over to Huffington Post to read the complete explanation.



Why You Hear What You Hear
An Experiential Approach to Sound, Music, and Psychoacoustics
Eric J. Heller


Preface [PDF]

Table of Contents [PDF]

Illustration Package




HOW CLIMATE WORKS (Part 9) — The Q&A session

Our video series on the HOW CLIMATE WORKS symposium held at Princeton University this past fall concludes with the Q&A session following the final talk of the day. We hope you have enjoyed your symposium vidoes. For furthur reading, check out our Princeton Primers in Climate series.

HOW CLIMATE WORKS (Part 8) — Caltech’s Andrew Ingersoll on Planetary Climates

Part 8 from the How Climate Works symposium brings us Andrew Ingersoll of the California Institute of Technology on planetary climates. This fall we will be publishing his book of the same toipc PLANETARY CLIMATES.

HOW CLIMATE WORKS (Part 7) — Shawn Marshall on The Cryosphere

Part 7 from the How Climate Works symposium features Shawn Marshall of the University of Calgary on the cryosphere. We published his excellent book on the subject in the Fall or 2011 called THE CRYOSPHERE.

HOW CLIMATE WORKS (Part 6) — Michael Bender on Paleoclimate

Continuing with our series on talks from Princeton’s HOW CLIMATE WORKS symposium, here we see Princeton University geoscience professor Michael Bender discussing Paleoclimate. His new book PALEOCLIMATE will be availble July 2013.

HOW CLIMATE WORKS (Part 5) — David Archer on the Global Carbon Cycle

Renowned University of Chicago geophysicist David Archer discussed the Global Carbon Cycle. We published the book of the same name, THE GLOBAL CARBON CYCLE, in the Fall of 2010.

Interview: How to Build a Habitable Planet author Charles H. Langmuir explains How to Build a Comprehensible Publication

1) The original edition of “How to Build a Habitable Planet,” written and published by Wally Broecker in 1985, is a legend within the university community for both its unusual breadth and clarity.  One of the first books on the Earth system, it did something very new by weaving together many fields that were traditionally kept separate — physics, chemistry, astronomy, all the Earth sciences, and biology — into one, jargon-free narrative.  What was the original inspiration behind the writing of this unusual book?


The growing interest in what NASA referred to as habitability.

2)  Since publication, this book been used more and more widely within introductory Geology and Earth Science courses, even inspiring courses built around the structure and contents of the book, entitled “How to Build a Habitable Planet.”  Did Broecker originally intend for the book to be used within courses?  What about this book makes it so ideal for course use?


The book breaks with the tradition of teaching Earth science as a collection of sub-disciplines—minerals, rocks, volcanoes, glaciers, plate tectonics, etc.  Instead, we try to have the reader learn where he or she comes from and how human beings are a consequence of an entire history beginning with the Big Bang.  So, the book combines the traditional “physical geology” and “historical geology” approaches and includes material from both of them in the context of the overall story of Earth’s evolution, its connection to the rise of Homo sapiens, and our influence and potential role on the planet.  Another aspect is the central role that biology plays in Earth’s evolution, and the importance of the interactions between all aspects of Earth, its interior, exterior, life and the cosmos.


3)  Charles Langmuir: You teach a course at Harvard – called, “How to Build a Habitable Planet.”  How did you originally start using the book in your course?  What is the background of the students in your course, and how many students does your course typically attract each year?  What do you hope your students will take away from taking your course and reading this book?


I started teaching the course, because I was working on the new version of the book.  I used draft chapters in the course and, through teaching it each year, the subject stayed alive.  I also saw what material engaged the students, and what material seemed tedious to them.  The Harvard course is a general education course — one that is designed for the non-science major.  Science majors find the course easy.  People who have not taken any science course for years can find it challenging. In my view every college student – actually, every educated human being – should know the essential elements of the story of the Earth and where we come from.  How can we engage effectively as modern citizens without such knowledge?  We do not necessarily need to know that glaciers make u-shaped valleys and rivers make v-shaped valleys, cool as that is; but, we do need to know where we come from and how we got here, and the implications that has for our planet. I hope that the students will be able to explain to their friends and family how we know the Big Bang is true, why plate tectonics and evolution are facts as well as theory, and the unique place that human beings occupy in human history – possibly marking the beginning of a new eon of geological time, should we survive that long.


The course at Harvard has 60 students in it this year. That, to me, is an ideal size, as it is possible to interact with the students on a personal basis and, at the same time, reach a group of significant size.


4)  A few years ago, you (Charles Langmuir and Wally Broecker) began collaborating on a newly revised and expanded edition of “How to Build a Habitable Planet.”  How did the idea for this collaboration and revision come about?


Wally pointed out that despite the book’s title, the book had no biology in it, and was weak in terms of its treatment of the solid earth.  I had been teaching half of a one semester course in introductory geology at Columbia using parts of the original book, so Wally asked me if I would like to add a couple of chapters to the original book, on plate tectonics and the origin of life.  I knew nothing about the origin of life, but loved the original edition and decided to take it on.   I then started to learn much more about many aspects of earth evolution, and the book gradually grew to its current size, as I realized that evolution, the rise of oxygen, and the recent work on the discovery of extra-solar planets all needed to be included, as well as the origin of life and more on Earth’s interior.


5) Why did you feel that a new edition was needed?  How is the new edition different from the original edition?


The new edition is far more comprehensive, with more than twice the number of chapters of the original edition.  Life is now central to the book, and the origin of life, evolution, the transformation of Earth’s exterior by life, and the connections among life, the solid Earth, atmosphere, ocean and cosmos are now a pervasive theme throughout the book.   Ocean ridges, convergent margins, mantle convection and the plate tectonic geochemical cycle are also major new additions.  All of the chapters, of course, are almost entirely rewritten to reflect the astounding growth in knowledge and understanding that has occurred over the last twenty-five years.


6) One of the later chapters of the book is called “Mankind at the Helm.”  How do you feel that the book informs new readers about the state of the art of climate science, and what the fate and role of our species is on our habitable planet, Earth?


We attempt to pose this problem in the context of our overall understanding of our planet. As a species, we are transforming the planet at a rate as fast or faster than many of the great era and eon boundaries of the past, and this is happening within our lifetimes.  It is astounding.  It is all made possible by our access to “Earth’s treasure chest,” which was gradually built up over billions of years of planetary history.  At the same time, a planet with intelligent life and civilization on it is a very different “being” than a planet without such capability.  For the first time there is the possibility of monitoring and understanding planetary systems, communicating with other intelligent life, should it exist, and transforming many planetary processes, including evolution and climate.


For climate science, we try to put the current situation in a larger context. It is not just that CO2 is rising, but that the rate of change is far faster then glacial to interglacial transitions, and that human emissions are several hundred times the emissions of volcanoes, which have been a major control on climate modulation over Earth history.  And Earth makes new oil at the rate that one gas station pumps gas.  We are using up hundreds of millions of years of Earth’s fossil fuel production in a few centuries.   These kinds of simple facts put the enormity of human actions in a different context than saying that CO2 is going up in the atmosphere by a few ppm per year and what the consequences are of that.


7)  You also write about planetary evolution and the role of extinctions and catastrophes in the history of a planet.  What are some of the ways in which catastrophes have affected our planet’s evolution in its history?


Catastrophes driving from Earth’s interior, the cosmos, and possibly life and climate have been a central aspect of Earth’s evolution.  Catastrophes interact with evolution in important ways, clearing out the ecospace so that new evolutionary innovations can flourish. Snowball Earth episodes may be related to the rise of oxygen.  Most mass extinctions seem to be associated with massive volcanism stemming from the core mantle boundary, and some associated with meteorite impacts.  Catastrophes are often at the same time disasters and opportunities.  The rise of oxygen can be viewed in the same way.  It was a toxic pollutant for anaerobic organisms, and is intrinsically harmful to organic matter, which breaks down in the presence of oxygen.  But, it also held the potential for an energy revolution in metabolism that permitted aerobic organisms and ultimately the rise of multi-cellular life.  It is important not to be naïve about change.  Change is inevitable.  It can be both crisis and opportunity.


8)  Some say that we are in the midst of a “6th extinction” event, largely caused by humans.  Do you think that there is evidence for this view?


Yes.  In the book we look at extinctions in terms of the “half-life” of organisms.  Looked at in that way, there is an objective assessment of whether the current extinction rate is unusual or not in a planetary context.  Life changes rapidly—there is almost complete species turnover in about 43 million years, based on the geological record. Human beings have accelerated extinction rates by ten thousand times relative to the background level that can be quantified for the Phanerozoic. If emergence of new species had been similarly accelerated, some 20% of Earth species would be new in the past two centuries.  This shows the magnitude of the human influence.  Mass extinctions of the past cannot be constrained to less than a few hundred thousand years.  We may be in the midst of one of the most rapid mass extinctions in planetary history; but, of course, it is not yet complete.  There is the possibility for us to preserve much of the biodiversity of the planet, but that seems unlikely without a major change in human behavior.


9)  Another of your chapters, entitled “Are We Alone?,” speaks to the fact that ~ 700 extrasolar planets have been discovered since the original edition was published.  What are some of the ways in which studying other planets and seeking other habitable worlds informs our understanding of our own planet’s climate and evolution?


Of course, this is one of the most exciting developments of modern science.  The discoveries to date have been constrained by the methods to exclude truly Earth-like planets (not only in terms of size, but also distance from their star), but that will change in coming years.  Perhaps the most exciting development will be if evidence is found for life anywhere else.  If it is, then life is pervasive throughout the universe.  It is very hard to know whether life is a natural, pervasive planetary process, or whether unique aspects of Earth’s history permitted it—right habitable zone in the galaxy, right habitable zone around a star, just the right volatile budget, a large moon, and so on.  But, if we find life any one other place, and we can only look at less than one in a billion places, then life is essentially everywhere.


The other important aspect is all the strange solar systems being discovered, so different from our own, greatly expand our understanding and imagination concerning life elsewhere.


10)  Since the original edition was so widely read, you must have heard stories from readers, about the effect that the book had on them.  Could you share one such story?  What effect do you hope this new edition of this classic book will have on its readers?

The most heartening comments are ones I commonly hear at the end of the course or in the evaluations, such as “I never knew science could be so interesting” or “Everyone should know this stuff!”  Just yesterday in office hours, one student said to me that she had been tutoring elementary school children, and they asked where the moon came from.  She told them about the giant impact theory, and she said the children’s eyes opened wide, and they became animated, asking all kinds of questions. One of them said, “Oh dear, what happened to all the people?”  To me, this reflected our natural human interest in our planet and where we come from, and the innate concern that is there within us, often submerged, for our fellow human beings.  In those two aspects of our nature, present in children, latent in all of us, may be a hope for the future.



bookjacket   How to Build a Habitable Planet:
The Story of Earth from the Big Bang to Humankind (Revised and Expanded Edition)

Charles H. Langmuir & Wally Broecker

Since its first publication more than twenty-five years ago, How to Build a Habitable Planet has established a legendary reputation as an accessible yet scientifically impeccable introduction to the origin and evolution of Earth, from the Big Bang through the rise of human civilization. This classic account of how our habitable planet was assembled from the stuff of stars introduced readers to planetary, Earth, and climate science by way of a fascinating narrative. Now this great book has been made even better. Harvard geochemist Charles Langmuir has worked closely with the original author, Wally Broecker, one of the world’s leading Earth scientists, to revise and expand the book for a new generation of readers for whom active planetary stewardship is becoming imperative.

“To be worth being this unwieldy, a book ought to do something pretty remarkable. And that’s just what How to Build . . . does, as you can tell from its subtitle, The Story of Earth from the Big Bang to Humankind. Now that’s what you call a large canvas.”–Brian Clegg, Popular Science

HOW CLIMATE WORKS (Part 4) – The Morning’s Q&A Session

For those following our HOW CLIMATE WORKS symposium videos, our latest addition is the morning’s Questions & Answers session.