Themes
Key
LitCharts assigns a color and icon to each theme in The Sixth Extinction, which you can use to track the themes throughout the work.
Mass-extinction and Morality
Natural Selection and Mass-extinction
Environmental Change and Human Nature
Science and Paradigm Shifts
Summary
Analysis
There is a small island in the middle of the Tyrrhenian Sea called Castello Aragonese. The island formed many millions of years ago, due to the pressure between the African and Eurasian tectonic plates—a phenomenon that sometimes causes the release of carbon dioxide gas. Kolbert travels to Castello Aragonese in the winter in order to investigate the carbon dioxide levels of the surrounding waters.
In the previous chapter, Kolbert brought up an important topic: the effect of atmospheric carbon dioxide levels on the Earth’s oceans. In this chapter, she’ll study the topic more closely. Castello Aragonese, because it is close to a tectonic plate, is a kind of “crystal ball” for scientists—the state of marine life there suggests what the oceans will look like in half a century.
Themes
At Castello Aragonese, Kolbert meets two marine biologists named Jason Hall-Spencer and Maria Cristina Buia. Buia and Hall-Spencer take Kolbert scuba diving and they show her the huge green bubbles rising from the vents in the sea floor. Near the vents, there is very little sea life.
Right away, the marine life at Castello Aragonese doesn’t look very healthy: the high levels of carbon dioxide in the water seem to be interfering with life (for reasons we don’t fully understand yet). If Castello Aragonese is a “crystal ball,” the future doesn’t look good.
Themes
Since the Industrial Revolution began in the early 19th century, human beings have burned huge quantities of fossil fuels (like coal, oil, and natural gas), a process that has added many billions of metric tones of carbon to the atmosphere. Humans have also cut down many trees, further increasing the amount of carbon in the air. At the current rate of growth, Kolbert asserts, humans can expect the carbon dioxide concentration of the atmosphere to become double what it was before the Industrial Revolution began. The average world temperature could increase by as much as seven degrees Fahrenheit, melting the world’s glaciers and dramatically changing the marine environment. The changes in temperature and sea level could then trigger further changes for the world’s ecosystems. The increase in carbon in the atmosphere is also tied to increased acidity of ocean water—indeed, ocean water is almost thirty percent more acidic than it was in the year 1800, and by the year 2050, Kolbert predicts, it will be 150 percent more acidic than it was in 1800.
One of the most important ways that human beings alter their environment is by burning fossil fuels. Indeed, the burning of fossil fuels has been a fixture of civilization since the Industrial Revolution (when scientists realized that burning coal could power a steam engine, and, later, that gasoline could power an internal combustion engine). Operating under an old paradigm, scientists believed that burning fossil fuels didn’t alter the Earth’s atmosphere in any major way; under the new paradigm, however, it seems clear that humanity’s fuel consumption will have major ramifications for the temperature and acidity of the oceans.
Themes
Back on land, Hall-Spencer and Buia show Kolbert some of the animals they’ve rescued from the ocean, including a starfish with a missing arm, and a large sea cucumber. The carbon dioxide-emitting sea vents of the ocean have eroded the shells of many sea creatures, considerably endangering their survival. In the waters surrounding Castello Aragonese, one can determine how close a sea creature lived to a carbon dioxide vent based on the erosion in its shell—the more erosion, the closer it lived. Furthermore, Hall-Spencer and Buia can study the sea-life near a carbon dioxide vent to predict what the Earth’s oceans in general will be like in another century. Based on the data at Castello Aragonese, entire ecosystems, comprising many different species, will vanish.
The most immediate impact of increased oceanic acidity on marine life is the erosion of sea creatures’ shells. Much like the ammonites in the previous mass-extinction, mollusks used to have a huge evolutionary advantage (their shells kept them safe), but now they seem to be at an evolutionary disadvantage (their shells erode easily). While humans aren’t directly responsible for the high acidity of water in Castello Aragonese (natural vents add carbon dioxide to the water), they’re responsible for the overall, rapid acidification of the oceans.
Themes
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In 2008, Hall-Spencer wrote an influential paper on the acidification of the oceans; since that year, there’s been considerable interest in the topic. Other scientists and research projects have confirmed Hall-Spencer’s basic point: carbon dioxide emissions will greatly decrease the quantity and variety of life in the oceans. Many small bacteria and plankton will thrive in the newly acidic oceans, consuming more nutrients and depriving larger creatures of nutrition. Acidification probably played a large role in at least two of the “Big Five” mass-extinctions, and it will probably play a major role in the sixth.
Again, notice how recent the scientific articles on ocean acidity are—only a decade old. The notion that human beings have the power to acidify the oceans is still unfamiliar to the average person. Therefore, it’s the duty of science writers like Kolbert to publicize this important information. Also, notice that increased acidity won’t kill all life in the oceans; as with previous mass-extinctions, some creatures will thrive in their new environment, while others will die out.
Themes
Ocean acidification is dangerous for many reasons. It deprives large animals of nutrition, interferes with photosynthesis, and wipes out existing ecosystems. One group of creatures that will be particularly harmed by acidification is calcifiers, or creatures that build themselves calcium shells (e.g., clams, oysters, sea urchins, barnacles, and starfish). Acidification wears away at marine animals’ calcium exteriors, which Kolbert compares to “trying to build a house while someone keeps stealing your bricks.”
Calcifiers are some of the most common animals in the sea, which means that, if the acidity of the oceans continues to rise, a significant chunk of the animals that live in the oceans will die out or have to adapt rapidly to their changing environments. A clam that cannot form a thick, durable shell will not be able to survive for very long—therefore, it’s possible that clams will go extinct.
Themes
In general, carbon dioxide emissions are particularly deadly for ocean life because oceans absorb about a third of the carbon dioxide that humans pump into the atmosphere. The problem, Kolbert argues, isn’t so much that humans have added carbon dioxide to the ocean (carbon dioxide is always entering the ocean in some form), but that they’ve added it to the ocean quickly, effectively “running geologic history … at warp speed.” If humans continue at their current rates, the Anthropocene epoch will be one of the most “cataclysmic” events in planetary history.
There is nothing unprecedented about the projected acidity of the oceans—as Kolbert says here, the oceans have experienced growing and declining acidity at many points in the history of the planet. Kolbert’s point is that humans are increasing the acidity of the oceans quickly—so quickly, in fact, that species don’t have enough time to adapt to their changing environments.
Themes
