Snowball Earth: The Story of a Maverick Scientist and His Theory of the Global Catastrophe That Spawned Life As We Know It [Paperback]

Of all the books I have read about climate change, "Snowball Earth", by Gabrielle Walker, is definitely one of the best ' and it's not even about the current climate change.

Part of what makes it so good is the style of writing. As the Los Angeles Times said about her later book, An Ocean of Air, 'Walker has a Ph.D. in chemistry, but she writes like a poet.' And, indeed, after an education at Cambridge, Walker has spent most of her career as a science journalist. It's sort of sad that this doesn't happen more often. Usually, those who understand a subject best are not the ones who communicate it. Walker is the exception to this rule.

Take, for example, this passage about the history of life on Earth: "Stretch your arms out wide to encompass all the time on Earth. Let's say that time runs from left to right, so Earth was born at the tip of the middle finger on your left hand. Slime arose just before your left elbow and ruled for the remaining length of your left arm, across to the right, past your right shoulder, your right elbow, on down your forearm, and eventually ceded somewhere around your right wrist. For sheer Earth-gripping longevity, nothing else comes close. The dinosaurs reigned for barely a finger's length. And a judicious swipe of a nail file on the middle finger of your right hand would wipe out the whole of human history."

Another impressive aspect of Walker's writing is her characterization. Wacky, stubborn, and exuberant scientists are brought to life. Instead of just hearing about their work and accomplishments, you feel like you're getting to know them as people. She writes about arguing scientists particularly well. Arguing scientists are so much fun to read about ' that's one reason I loved The Lost World by Arthur Conan Doyle.

However, the best part of this book, by far, is the subject matter. The theory of Snowball Earth is possibly the most awesome thing I have ever heard about. Here's how the story goes:

From what paleontologists can see preserved in fossils, complex life arose at a very specific point in prehistory: the end of the Precambrian. For several billion years before that, the only thing that lived on Earth was unicellular goop. But then, suddenly, all at once, complex organisms burst onto the evolutionary stage.

Something must have caused this dramatic appearance, and a series of scientists from the 1940s on ' most prominently, Paul Hoffman ' likely have discovered what. At the end of the Precambrian, there are signs of ice in rocks all over the world ' scratches, rock deposits, everything that led Agassiz to discover the ice ages.

Because plate tectonics moves everything around so much, though, rocks were not necessarily formed at the location they sit today. Their magnetic field is what discloses their birthplace. Tiny bits of magnetic material, such as iron, line their field up with the Earth's. The Earth's magnetic field is perpendicular to the surface at the poles and parallel to the surface at the Equator. So, if a rock's magnetic field is vertical, it was formed at the poles. If it is horizontal, it was formed at the equator.

Incredibly, scientists found Precambrian rocks, with signs of ice, with horizontal magnetic fields. During that period of prehistory, the equator was covered in ice ' and, therefore, the whole planet, because it's not really possible to freeze the equator without freezing all the other latitudes too.

The scientists determined that, for several instances on the Precambrian, the continents were arranged in a way that was very conducive to ice-albedo feedback. With the smallest trigger, ice from the poles would creep across the temperature zones and meet at the equator. Frozen oceans, frozen land, the whole bit.

And now CO2 comes into the story. Volcanic eruptions naturally release carbon dioxide, but the amount is so small that the oceans have no trouble soaking them up ' unless they're frozen on the surface and cut off from the air. CO2 would gradually build up, in that case, and millions of years later, the greenhouse effect would be so strong that all the ice would melt and the planet would plunge into a state referred to as Hothouse Earth. Then the oceans would start absorbing all the extra CO2, and ice would reappear at the poles, and the cycle would begin again.

Many scientists believe that these Precambrian cycles of extreme heat and extreme cold provided such a strong pressure on organisms that natural selection was pushed to new boundaries. Complex life had an advantage in these extreme conditions, and it flourished. The most catastrophic climatic event our planet has ever experienced, in our knowledge, was what led to the evolution of multicellular organisms, and eventually, us.

It makes me feel very small, the same way that attempting to comprehend the vastness of the universe makes me feel very small. The life we see all around us only exists because of a series of coincidences. Human beings, one of the youngest of the millions of animal species that have ever existed, are alive because of continental drift lining things up in the right way. And who knows what would have happened if things had been slightly different?

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I will start with a brief synopsis of the science. In the last six years, many scientists have come to think that an ice age of incredible severity gripped the Earth for a few million years, ending about 590 million years ago. The ocean surface apparently froze all the way to the equator, although the ice may have been thin and patchy near the equator. The Earth's average temperature was about -40 degrees Fahrenheit. Volcanoes belched out greenhouse gases for a few million years, and the atmospheric CO2 levels rose to many times what we have today. The ice receded from the tropics, and the greenhouse effect accelerated, driving the average planetary temperature above 100 degrees Fahrenheit (compared to about 60 today) within a few thousand years or less. This super ice age was the last of 4 to 6 such ice ages, with the first one occurring about 2.4 billion years ago, and the others between 750 and 590 million years ago. These ice ages may have occurred when all of the continents were strung around the equator. (The book presents a theory on why this might be so.) Finally, complex multi-cellular life forms first appeared in the Ediacaran period, shortly after the last super ice age. The book suggests that the last super ice age somehow spurred the appearance of complex life, but does not provide a good explanation of why this might be. (Maybe there is an assumption that "right after X" must mean "because of X.") Finally, the book asserts that such a calamity may occur again about 250 million years in the future.

The book is oddly written: part biography and part detective story, with some science scattered throughout. At no point does the book lay out a comprehensive exposition on the snowball hypothesis. Rather, the scientific theory comes through in bits and pieces as the book goes along. The book is, in large part, a biography of the four men who invented the snowball Earth theory: Paul Hoffman, Brian Harland, Joe Kirschvink, and Dan Schrag. It presents lots of extraneous information about these four guys, especially Hoffman (e.g., his exploits in running marathons). The book hops back and forth between the lives of the fantastic four, all the while letting the scientific mystery play itself out. This is something like a detective story. Many readers will probably like this approach, but I would have preferred that the first chapter explain the "snowball Earth" theory in detail. The rest of the book could then have dealt with how the theory came about, and the people who invented it. Moreover, the book is too narrowly oriented towards geology. Additional emphasis on atmospheric sciences, biology, and astrophysics would have been welcome. (For example, the sun's luminosity has increased about 1% every 200 million years for the last 3 billion years. During the various snowball epochs, the sun's brightness was about 88% to 97% of today's value. At what point is the sun too hot to allow a snowball epoch?)

The book also contains some errors. For example, it states that bacteria survived a trip to the Moon on an Apollo mission in 1967. The first Apollo moon landing was in 1969. Also, the book fails to consider the possibility that complex life may have provided an additional feedback mechanism for regulating CO2 levels in the air. In other words, it may have been that complex life caused an end to the snowball epochs, more so than the snowball epochs stimulating the appearance of complex life.

Finally, the book should, but does not, have pictures, illustrations, and maps.

This book offers a fascinating look at a possible explanation of how life went from single cell organisms to multicellular organisms. Also shows how different scientists can view and interpret the same data in different ways to support their different views. I have a lot of respect for Ms. Walker. Not only does she interview the main scientists that are involved in this debate, she has gone to some pretty remote areas of the world to see the very rocks that these scientists are basing their views on. That is alot more than most people would expect from someone just relating a story.

If you are interested in early life on Earth, you should read this book. If you are interested in how science tries to determine what has gone before, you should read this book. In short, if you are curious about life/science/the earth , "read this book."