What does it take to change the world? Change it, that is, on a geologic scale that can withstand the rest of deep time? Meteoric impacts have succeeded: one blasted the Moon out of the Earth. Others have caused mass extinctions. Volcanic eruptions have certainly left their mark, too, burying areas the size of California under lava flows a mile deep. In contrast, the creatures that crowd the surface of our living planet rarely have a detectable impact on the global environment. Even the dinosaurs that ruled the Earth for a hundred million years left a legacy of little more than mineralized bones and footprints in rock.
On a very few occasions, however, life stepped up to the big leagues. In two of the best-known examples, world-changing algae and plants caused disastrous environmental shifts that lasted millions of years. Humans are world changers 3.0—the first animals to make the list. Our evolutionary success is undeniable, and our means of changing the planet have more in common with those of our predecessors than one might suspect. Our disastrous environmental shift is impending, with one key difference. We can see it coming—and we can avoid it. Whether or not we will remains to be seen.
The evidence of life’s imprint on Earth is not as immediately apparent as volcanic eruptions, but it can be seen in subtler clues, such as the red rocks of the southwestern desert or the Hawaiian Islands of the United States. The same is true for the southeastern red sands of Tara in Gone With the Wind, and the red rocks that are ubiquitous in central Massachusetts around Amherst College, where I went to school twenty-five years ago. Our sedimentology professor, Edward S. “Ed” Belt, was so enthralled by those rocks that we made T-shirts asking, “Whence the red beds?”—a favorite query of his. We picked the quote in mock tribute to what we saw as Belt’s eccentricities, which included a zeal for backing up highway off-ramps in pursuit of the perfect rock outcrop. I’ve since come to realize it is a question that strikes at the core of how life can change the planet.
The red rocks of Amherst and other locales around the world, as Belt taught us, are red because they contain rust—iron combined with oxygen. But the oldest
completely red sediments are not very old, as rocks go: they date back about 2.2 billion years, roughly half the age of the Earth. Many older sedimentary rocks exist, but they are never red throughout, because the first half of Earth’s history took place under an atmospherethat contained no oxygen. Today our atmosphere contains 21 percent oxygen—without which life as we know it would be impossible, and no creature on Earth would be larger than a single cell. No other known planets have free oxygen in their atmospheres. Why does ours?
As early as 1774, the theologian Joseph Priestley noted that fire and the breath of animals “foul” the air. That is, they consume oxygen. Priestley reasoned that there must be a process that restores oxygen to the atmosphere, or else, over time, Earth would run out of breathable air. He even deduced that plants played a part in this restorative function. But it would take almost two centuries before scientists pieced together a relatively complete history of our atmosphere and the role life played in making Earth what it is today.
Around 2.7 billion years ago (the exact date is still hotly debated), a group of single-celled organisms started down the evolutionary pathway to becoming world changers 1.0. They invented a new way of doing photosynthesis that produced oxygen as a waste product: allowing organisms to use the Sun’s energy to capture carbon dioxide (CO2) from the environment and turn it into the carbonbased molecules that make up all known life. Oxygenproducing photosynthesis is much more efficient than other, more primitive versions, and by capturing more energy from a given ray of sunlight, world changers 1.0 could grow faster than their competitors.
Cyanobacteria, or blue-green algae, proliferate in the Great Lakes. The planet was never the same after these organisms found a new way to harness energy (from the Sun) and jettisoned their waste (oxygen); the second big shift occurred when land plants began sucking massive amounts of CO2 from the air 450 million years ago.
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By itself, enhanced access to energy probably wasn’t sufficient to change the world. The early photosynthesizers still needed a way of getting all the other nutrients required for growth. In the early ocean, the scarcest of these was probably nitrogen, a key element in DNA, protein, and nearly all the other molecules of life. Nitrogen’s scarcity is paradoxical, because it is abundant in the air, but in a chemical form that organisms can’t use. The biogeochemist James N. Galloway, at the University of Virginia, studies nitrogen’s outsize role in the environment and emphasizes this point in his teaching with a riff on Coleridge’s “Rime of the Ancient Mariner.” “Nitrogen, nitrogen everywhere, but nary a molecule to use” may be lousy poetry, but it’s an apt description. Very few organisms can transform nitrogen in the air into a useful form, and this process of “nitrogen fixation” costs those organisms a lot of energy.
Nitrogen fixation evolved very early in the history of life, but the blue-green algae, known to most of us as pond scum, combined nitrogen fixation with oxygen-producing photosynthesis sometime around 2.7-3 billion years ago. Is so doing, they became world changers 1.0. Blue-green algae proliferated across the open ocean, using the sun’s energy they captured so efficiently to fix the nitrogen they needed. At first, it didn’t matter that they were dumping their waste product, oxygen, intothe environment. But exploiting new sources of energy and food can come with unintended consequences.
Which brings us back to red rocks. For hundreds of millions of years, blue-green algae pumped out oxygen, but chemicals in the oceans consumed it. Nothing much changed. Then, around 2.2 billion years ago, those chemicals were used up, and oxygen began to bubble up out of the ocean and into the air. And the oxygen began to react with iron in coastal sediments. Thence, the red beds. And the changes went far beyond Earth’s color palette.
“The Great Oxidation Event” was the single biggest change life has ever made to the planet. For an organism trying to survive the transition in the sunlit upper ocean, it must have been hell. Almost all organisms in the ocean had evolved in the absence of oxygen, and key biological processes were poisoned by it. Free oxygen destroyed the atmosphere’s methane, the greenhouse gas that kept the planet warm under the faint young sun. That helped induce the first global glaciation, which may have lasted hundreds of millions of years. Even the eventual evolutionary winners, which included the blue-green algae, must have experienced huge population crashes as ice covered the oceans and blocked out the Sun. The tree of life was reshaped forever. All because a group of organisms found a new way to get energy and use it to make food—and dumped their waste products into the environment
The key to changing the world is chemistry, and the chemical tools of all world changers are similar: novel access to energy and nutrients. To illustrate this, let’s move on to world changers 2.0—the land plants. They emerged 450 million years ago, fully two billion years after the Great Oxidation Event. While 450 million years ago is still very deep time, by this point 90 percent of Earth history had already occurred. The oceans and atmosphere had present-day levels of oxygen. There were fish in the sea—but not much life on land.
The success story of land plants begins, once again, with energy. The earliest colonizers did not evolve a new way to get energy (plants use the same oxygen producing photosynthesis as the blue-green algae), but they moved to an untapped source—land. For approximately 100 million years they stayed near rivers and in swamps, apparently unable to move to drier areas. Like their predecessors, world changers 2.0 were slow to have an impact. Then trees, most of which looked like a pine tree crossed with a giant fern, began to move inland. Like the blue-green algae, land plants used ready access to the Sun’s energy to overcome the limitations of their environment: they took the carbon they could capture through photosynthesis to build deep roots which probed for water and broke down rocks to access nutrients. In the oceans, “rock-derived” nutrients (such as phosphorus and potassium) are scarce, supplied only by dust blown off the continents and the trickle of rivers. Land plants went right to the source, and by 350 million years ago the first forests proliferated across then-tropical continents.
Anyone lucky enough to be in a tropical rainforest probably spends more time looking up than down. But kick aside the thin layer of leaves, push through a few inches of black mud, and one usually finds red dirt similar in color to those rocks in Massachusetts. On the island of Kauai, Hawaii, for example (where I have worked for over a decade), there are myriad roadside kiosks hawking “Red Dirt Shirts.” My research has circled back to what red dirt tells us about how the world works. Ed Belt’s question is still ringing in my ears.
Tropical soils are red because warm, wet conditions leach out most elements and leave behind hard-to-dissolve substances such as iron. Plant roots chemically accelerate this breakdown, and the reaction happens to consume CO2 from the air. When plants colonized land, CO2 was the major greenhouse gas keeping the planet warm—so warm that virtually the whole planet had a tropical climate.
In the course of building forests filled with wood (which is CO2 captured by photosynthesis and stored in plants) and promoting the chemical breakdown of rocks, land plants began to suck CO2 out of the air. Over the next 100 million years, CO2 levels dropped tenfold. As we are becoming all too aware, changing the CO2 levels changes the climate. As CO2 levels fell, the Earth began to cool. By 300 million years ago, the vast tropical forests that dominated the land were gone, frozen by their own success. Glaciers spread, wet regions became arid, and many flora and fauna went extinct. Once again, to the winners came hard times as they became victims of their own successful chemistry.
Which brings us to humans—world changers 3.0. The great creatures of bygone eons—dinosaurs, giant insects, and woolly mammoths—may capture our collective imaginations, but they had little effect on the chemistry of the planet. In this respect we have much more in common with the blue-green algae and the and plants.
The success of our species stems from the discovery of a new source of energy—fossil fuels—and the harnessing of that energy to get nutrients to feed a rapidly growing and spreading population. Thus, our link to the land plants is direct, because coal is the compressed remains of the great tropical forests that drove themselves out of business 300 million years ago (petroleum most often comes from aquatic plants and animals.) In burning coal, we’re simply using the sunlight energy captured by photosynthesis and stored by land plants, releasing CO2 as waste. Like the blue-green algae, we need the energy that comes from the combustion, not the waste. And, like them, we are using the energy to get food.
Soy bean fields in Mato Grosso, Brazil, now produce as many soy beans per acre as farms in Iowa, as a result of massive inputs of phosphorus to what were very nutrient-poor tropical soils.
In the run-up to World War I, the German chemist Fritz Haber came up with a benchtop way to mimic the nitrogen fixation performed by blue-green algae. Haber went on to invent horrific chemical weapons used in both world wars. But the industrialization of his apparatus, the Haber-Bosch process, now supplies more nitrogen fertilizer to farms as is fixed by all nonhuman organisms combined. Vaclav Smil, one of the leading environmental scientists of our era, calls it “the most important invention you never heard of.” It has allowed food production to triple since 1950. We could only produce enough food for half the current population without Haber-Bosch–derived nitrogen.
All this added nitrogen is a good thing for food production, but has unintended consequences off the farm. Some is transformed back into gases that cause global warming, ozone depletion, acid rain, and smog. Excess nitrogen poisons drinking water in agricultural areas and leaves rivers and coastal regions choked with algae that feed on it just like we do. By monkeying with a key nutrient, we’re reshaping the world’s ecosystems in ways we are only starting to understand.
As world changers 3.0 we’ve taken things even further. Our combination of fossil fuel burning for energy and nitrogen fixation by Haber-Bosch is reminiscent of how the blue-green algae took over the ocean 2.5 billion years ago. But we mimic the land plants as well. They succeeded not just by getting access to energy no other organism could get, but also because their roots could accelerate the breakdown of rocks and release the nutrients they contained. We’ve figured out how to do that, too.
Much of my current research focuses on how tropical forests get and use rock-derived nutrients (I’m still chasing answers in the red dirt). But a few years back a graduate student walked into my office with a photo that sent me in a whole new research direction. She showed me a giant soybean field in what used to be the Amazon rainforest. During the dry season, the barren soils are bright red, leached by millions of years under a tropical climate. But this time, it wasn’t the red that caught my eye; it was the lush green fields that thrive during the wet season on some of the poorest soils in the world. Soy production in Brazil is booming, and reshaping the global food supply.
The boom wouldn’t exist without massive inputs of rock-derived nutrients, particularly phosphorus, from mines all over the world. Mining is our way of mimicking what the land plants did 450 million years ago. World changers 2.0 used the sun’s energy to capture CO2 and used it to build roots, which broke down rocks and released nutrients. We use the stored sunlight energy in fossil fuels to run the machines that mine phosphate ore and convert it to fertilizer that we ship around the world.
To change the world, we’ve borrowed techniques from each of our predecessors—finding a new source of energy, getting access to nitrogen in the air, and breaking down rocks to access their nutrients. But version 3.0 is much faster. Absent radical shifts in energy policy, we will double the amount of CO2 in the atmosphere by 2050, merely 200 years after the Industrial Revolution. The land plants took 20 million years to have a similar-magnitude effect. Haber-Bosch has doubled the total available nitrogen on the land surface in fifty years. Blue-green algae probably did the same for the oceans over several hundred million. Our mines have quadrupled the amount of phosphorus being “weathered” out of rock. It took the land plants 100 million years to leave the river valleys and creep across the continents.
Salt Lake City, Utah, glows at night with the energy harnessed by fossil fuels;our waste, released as CO2, is changing the world at breakneck speed.
Viewed in this light, it is inconceivable that our domination of the planet wouldn’t change the world. But for all our similarities with versions 1.0 and 2.0, we have one very important difference. We know what we are doing. We have taken over the climatic and nutrient dynamics of the planet. If we choose, we can manage these chemical rhythms wisely, rather than by neglect. Blue-green algae had no choice but to dump their waste products into the environment. We do.
Ed Belt taught me that the present is the key to the past. By observing the way the Earth works today, we can deduce what might have happened long ago. But I now realize the lesson cuts both ways. In this era of massive global change, the past can help us understand what the future holds if we tinker too much with the fundamental chemistry of the planet. And the first lesson is this: living through big changes in Earth’s chemistry is neither easy nor guaranteed. And making those changes faster than life has ever done so before is terrifying.
Second, we should not be lulled by Earth’s inertia. It took at least several hundred million years of photosynthesis to oxygenate the atmosphere. It took about the same amount of time for land plants to cool off a global hothouse. At the time, it would have appeared that the Earth would always be as it was. And then it wasn’t.
I am not predicting that humans will go extinct as a result of our relentless quest for energy and food. Plenty of people will be fine living in a warmer world. Plenty of people can live with algae-choked waterways. We may end up mining asteroids or the deep sea to satisfy our phosphorus habit. Not everyone sees radical pruning of the tree of life as a violation of a moral imperative. There is no doubt that life will be possible, even abundant, no matter how we shake up global chemistry. Yet living through the transition will not be pretty. Unlike the blue-green algae, or the first tropical trees, we can see the changes coming and we know what has come before. We must use that knowledge to slow the change, and buy time to prepare.