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.

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