The Universe Within (22 page)

Colbert was a longtime fossil
hunter, and the sirens went off in his head. Opportunity knocked; here was a continent completely
unexplored for
fossils. Colbert wasted no time assembling a dream team of experts from the United States and South
Africa, who from years of working on the rocks of this age had the eyes to find new fossils. If fossil bones were present in Antarctica, this was the team to find them.

Almost from the moment their boots touched the Antarctic
sandstones, Colbert and his team had a field day picking bones from the sides of barren hills, where fossils were virtually everywhere they looked. One creature had a body shaped like a medium-sized dog, only instead of a jaw like a carnivore it had a large birdlike beak. What stopped Colbert in his tracks was not this creature’s bizarrely chimeric form but something far more mundane: paleontologists had known of this creature for decades. In the 1930s, South African geologists identified an entire layer that contains thousands of them extending across a wide swath of the Karoo Desert. This so-called
Lystrosaurus
Zone even reaches
South America,
India, and
Australia. Now, with a
Lystrosaurus
level in Antarctica, Colbert and his colleagues uncovered yet another clue exposing the reality of
continental drift. With the match of the rocks, coastlines, and fossils, a new view of Antarctica emerged: the continent in the past sat as a keystone at the center of a vast
supercontinent that included Africa, Australia, and India. This clump of continents covered much of the southern part of the planet.

The pile of fossils that Colbert’s group discovered revealed another fact of Antarctica’s past.
Lystrosaurus
, like the amphibian that led him there in the first place, was a cold-blooded animal that could live only in warm tropical or subtropical climates; think big salamanders or
lizards. Ditto the fossil
plants. Colbert and his team labored near the center of a vast frozen continent, close to where
Robert Falcon Scott and his party froze to death nearly sixty years before. But everything inside the rocks pointed to one conclusion: Antarctica was once a warm and wet world teeming with tropical life.

Expeditions that followed Colbert’s only exposed more of
Antarctica’s disconnect between its frozen desolate present and its lush past. The world that Colbert uncovered was followed by another filled with
dinosaurs and their kin. In rocks even more recent, 40 million years old, this tropical continent was home to modern rain forests,
amphibians, reptiles, birds, and a whole menagerie of mammals. For most of its history, Antarctica was a paradise for life.

Then, starting 40 million years ago, the entire continent went into the
freezer, and with it Antarctica witnessed the greatest and most complete extinction of any continent in the history of the planet. From a world rich in plants and animals, virtually every land-living creature simply disappeared.

There is symmetry to
Tudge’s flight near the
North Pole and Colbert’s exploration of the South: one unveiled temperate forests, the other tropical animals in regions that today house frozen deserts. The story of the poles is that of the entire planet. Our present—with its polar ice—is an aberration. For most of history our planet was warm, almost tropical. If the rocks of the world are a lens, they reveal that our modern, relatively cold landscape is not the normal state of affairs for the planet.

In this great
cooling lies one of the major events that shaped our bodies, our world, and our ability to see all.

Carl Sagan once spoke of a paradox about our planet’s climate. The
sun is not a constant beacon of light; it started its stellar life as a relatively dim star over 4.6 billion years ago and has increased in brightness ever since, being about 30 percent brighter and warmer now than when it formed. With such a dramatic increase in
heat over the years, Earth should have been a frozen waste in the past and now be a roiling cauldron of molten
crust. Yet all our thermometers for the planet paint a different picture.
Glaciers exist today during an era when the
temperatures should be downright hellish. There are signs of liquid water inside 3-billion-year-old rocks—at a time when
Earth should have been a ball of ice. Sure, we’ve had our moments of hot and cold, but if you think about Venus’s
surface temperatures of 900 degrees Fahrenheit and Mars’s of -81 degrees, Earth has been a stable Eden relative to its celestial neighbors. Somewhere on the planet lies a thermostat that buffers it from dramatic extremes in temperature.

Inroads to the thermostat were discovered by a student who was as persistent as he was headstrong. He started his graduate career by loudly proclaiming to his thesis adviser that he had a brand-new theory of electrical conductivity. The response to this arrogant introduction was a simple “good-bye.” Perseverance paid off, and, probably to the relief of his teachers, in 1881
Svante Arrhenius moved to Stockholm to work with a professor at the Academy of Sciences there. After that gig, Arrhenius went on to think of other scientific problems.

One scientific puzzle was right in front of Arrhenius’s eyes. He saw the factories of the Industrial Revolution belching
coal smoke—in his words, “evaporating our coal mines into the air.” Arrhenius knew from previous work that
carbon dioxide, a major constituent of the fumes, could capture heat. He made a few calculations that revealed how increased carbon dioxide in the air would trap heat on Earth and raise global temperatures. This idea was to lay fallow for a number of years, during which time Arrhenius won the
Nobel Prize for work derived from the seemingly lackluster doctoral thesis that had so annoyed his professors.

The famous
greenhouse effect is based on Arrhenius’s work. The more carbon dioxide there is in the atmosphere, the more heat is trapped by the planet and the hotter things get. Of course the reverse is true. But there is a deeper meaning to carbon in
the air, one that emerges only when you take the long view on timescales that extend millions of years in the past.

The television character Archie
Bunker once famously said of beer, “You don’t own it, you rent it.” The same holds true for every
atom inside us; we are the temporary holders of the materials that compose our bodies. Few of these
constituents are more important to the balance of life and the planet than
carbon. The connection among parts of Earth depends on how carbon moves through air, rock, water, and bodies. To see this chain of connections, we need to consider living things, rocks, and oceans not as entities in their own right but as stopping places for carbon as it marches along during our planet’s evolution.

Viewed in this way, the amount of carbon in the air depends on a delicate balance of conditions. Carbon in the atmosphere mixes with water and rains down to the surface as a slightly acidic precipitation. We see the effects of this in our daily lives; in my
university, built largely in the late nineteenth century, few gargoyles still have faces.
Acid rain works on exposed rock everywhere—on mountainsides, rubble fields, and sea cliffs. Once the acid rain breaks down rocks, the water—now also enriched with carbon that was inside the rocks—eventually winds its way through streams and rivers into the oceans. At this point the carbon gets incorporated into the bodies and cells of the creatures that swim there: seashells, fish, and plankton. When sea creatures’ remains, loaded with carbon, settle to the bottom of the ocean, they ultimately become part of the seafloor. And, as we’ve known since Marie Tharp, Bruce Heezen, and Harry Hess, the seafloor moves, only to be
recycled deep inside Earth.

This chain of events removes carbon from the atmosphere, taking it from the air and moving it to the hot internal crust of Earth. Alone, these steps would pull all the carbon out of the air, leaving Earth freezing with no
atmospheric insulation. The good news is that there is a recycling mechanism for carbon. Carbon in the interior of Earth gets injected back into the atmosphere by
volcanoes that eject gases. That is the long-term source of much of the
carbon we breathe: while
acid rain and the weathering of rocks remove carbon from the air, volcanoes emitting gases return it. Volcanoes typically release huge amounts of water vapor, carbon dioxide, and other gases; by some estimates they send over 120 million tons of carbon dioxide into the air each year.

Like a sequence of events in which each step makes sense but the end points are counterintuitive, the conclusion to draw from carbon’s movement is that rock
erosion and weathering is linked to climate. Rock erosion by acid rain is like a giant sponge that pulls carbon dioxide from the atmosphere. Lowering the amount of carbon dioxide in the air will drop the planet’s temperature. On the other hand, planetary events that increase the amount
of
carbon in the air—enhancing
volcanic activity or slowing removal of carbon from the air—will, of course, serve to raise temperatures. All else being equal, increasing
erosion of rocks leads to lower temperatures, decreasing erosion to higher ones.

The movement of carbon links rocks to climate and ultimately answers
Sagan’s paradox about the
sun. The planet’s temperatures are kept within a narrow range by the movement of carbon molecules through air, rain, rock, and volcano. Hot weather leads to more rock erosion, which leads to more carbon being pulled out of the air and thus colder weather. Then, just as things get colder, the cycle moves the planet’s temperatures in the opposite direction: colder weather leads to less erosion, increasing amounts of carbon in the air, and hotter temperatures. Liquid water is possible on our planet only because of this balance; neither we nor the landscapes we depend on could exist without it. But liquid water is like the miner’s canary. Too much of it, or too little, reveals a long-term shift in workings of the planet, changes that amount to planetary fevers and chills.

What happened when the
poles started to
freeze about 40 million years ago? The shift from hot to cold occurred at the same time that the levels of carbon in the atmosphere dropped precipitously. But this begs the question: What changed the levels of carbon in the air?

Maureen “Mo” Raymo went to school to study climate and the kinds of geological changes that could have an impact on it. And, like
Arrhenius, she produced a thesis that elicited memorable comments from advisers. One went so far as to comment that her Ph.D. dissertation was “a total crock.”

Her path to that fine moment began like any other graduate student’s: she took a string of classes representing the core knowledge of her field. In
geology seminars of the 1980s, much of the buzz was about global carbon and
Earth’s thermostat. A classic
paper, read by every student at the time, written by
Robert Berner,
Antonio Lasaga, and
Robert Garrels, described this link in
chemical detail. The paper became affectionately known as BLaG after the initials in the last names of each author. Everybody read BLaG and everybody was tested on BLaG, even though virtually everybody, including the BLaG authors themselves, realized key details of their brilliant model had yet to be filled out.

Raymo took the standard class for graduate students where the details of BLaG were presented. She also took classes on modern rivers,
mountain formation, and tectonics. But unlike the rest of us who sat through this kind of curriculum, she began to connect the dots.

Everybody knew that the climate cooled drastically starting 40 million years ago, but there was no known geological mechanism that could possibly have done this. What could drop the
temperatures? Only a major planetary change could possibly have removed enough carbon to allow such cooling.

Then Raymo looked at a globe and remembered her
plate tectonics. The period of drastic cooling commenced at a pivotal time in the history of the planet. This was when the continental plate
of India, which had been traveling north for hundreds of millions of years, began to slam into Asia. The result of this collision is like sliding two stacks of paper along a tabletop until they scrunch together: they crinkle and rise. A similar kind of mashup of the continents led to the rise of the
Tibetan Plateau and the
Himalaya mountains.