The Sixth Extinction: An Unnatural History (2014)

Kolbert references an undergraduate study conducted at Harvard in 1948 that focused on perception, how it changes, and why it changes. Thomas Kuhn, a famous twentieth-century scientist, was fascinated by this playing card experiment because “it revealed how people process disruptive information” (92). Man’s first instinct is to push that information into familiar and known settings, and any signs of anything amiss or out of the ordinary are ignored until they can’t be avoided any longer. That moment of crisis is called the “My God! reaction” by scientists (92).

To Kuhn, this experiment’s results made perfect sense. Any information that didn’t fit the accepted theories, standards, or beliefs of the day would be dismissed or explained away for as long as possible. From this concept came Kuhn’s term “paradigm shift,” or, in his words, “novelty emerging only with difficulty” (93), which was, in essence, his explanation for why scientists were so reluctant to abandon old traditional modes of thinking for newer, more accurate ones.

Broad paradigm shifts in scientific thinking were prompted by the paradigm shift that acknowledged the cataclysmic events that had caused mass extinctions. While Lyell and Darwin had stubbornly argued that extinction was a slow, lonely event, the Alvarezes’ discovery provided proof that catastrophes had happened and that whole species could be wiped out in a short time. The reluctance to embrace the Alvarezes’ stance, and its slow acceptance, is an example of Kuhn’s paradigm shift.

To further explore this paradigm shift, Kolbert visits Scotland, where she examines the rocks in Dob’s Linn, which date back roughly 445 million years to the end of the Ordovician period. That was a time when the land on earth was one conjoined mass, and a time directly following the prolific Cambrian period, when a multitude of new life forms appeared. During this time, the first reefs appeared, and the first plants began to grow and spread on land.

Then, 444 million years ago, nearly 85 percent of marine species died off. Initially, scientists thought a small catastrophe had happened at this time, but today this moment is considered the first of the Big Five extinctions, an extinction caused by a natural force.

In Scotland, Kolbert discusses the graptolite, a small marine organism that thrived before the end of the Ordovician period, then nearly died out in the extinction event that followed. The sensitive and delicate frame of these creatures meant they made excellent fossils for identifying the ages of successive layers of rock. Kolbert describes the physical changes that occurred in this small animal over time, some of its attributes being lost forever. She draws a comparison between the tiny graptolite and the mighty dinosaurs, both being “highly successful form[s] relegated to oblivion” (99).

By 1984, scientists had determined that aside from the five major mass extinctions, there had been lesser extinction events as well. They argued that extinctions occurred periodically, which spawned theories such as the “Nemesis” star or “death-star theory,” which was alternately celebrated and panned in the media. Luis Alvarez went so far as to travel to southern China to obtain rock samples, expecting to find iridium levels on par with those in Gubbio, only to be disappointed when the levels were minuscule at best. Eventually, the iridium levels were “attributed to the vagaries of sedimentation” (102).

Gradually, the theory developed that the mass extinction at the end of the Ordovician was caused by climate change, specifically glaciation. A greenhouse climate had rapidly changed at this time, with carbon dioxide levels dropping. Temperatures fell, sea levels dropped, the ocean’s chemistry changed, and animals died off, including the graptolites.

This situation contrasts with the extinction event at the end of the Permian period, when a massive release of carbon into the air raised temperatures to the point where species were eliminated. Kolbert thus theorizes that each mass extinction event was unique unto itself. All they have in common is “the very freakishness of the events …[;] all of a sudden, organisms find themselves facing conditions for which they are, evolutionarily, unprepared” (103).

Kolbert considers the role of human beings in current times, and what our role will look like to scientists of the future. According to her Scottish guide, Zalasiewicz, “We have already left a record that is now indelible” (105). For example, Kolbert discusses the nomadic movements of human beings, and how those travels have wrought unexpected and unplanned havoc on the environment. She uses rats as a prime example of creatures that have been found in all corners of the world and could only be there because they traveled with humans to those places. Rat populations then exploded due to a lack of predators, and in some areas of the world, the number of rats caused irreversible impacts on other species. Kolbert cites the Norway rat (actually from China) as destroying reptile and bird populations and creating its own “ecospace” (105).

Scientists have argued about what to call the current age of the Earth, and it was Danish chemist Paul Crutzen who used the word “Anthropocene” to describe this most recent epoch, beginning 11,700 years ago. Crutzen felt the term was wholly appropriate due to the dominance of humanity during this period and to the geological changes that have occurred due to human activity. Crutzen’s suggestion convinced Zalasiewicz, and, as the head of the Anthropocene Working Group, he hopes to have the term officially accepted and adopted as the name of the newest and current epoch.

Kolbert next visits the tiny island of Castello Aragonese, just west of Naples, due to its formation by the pressure of the African and Eurasian plates pushing into each other. This phenomenon causes gas to vent out of the sea floor, a gas that is almost wholly carbon dioxide. Kolbert is given a chance to see the vents with two marine biologists, Maria Christina Buia and Jason Hall-Spencer. In the water, Kolbert examines sea urchins and other marine life, but she notes that the closer they get to the bubbling vents, the less marine life they find.

Kolbert relates this expedition to the ecological damage done by human beings since the start of the Industrial Revolution. The burning of fossil fuels and deforestation have added significant amounts of carbon to the atmosphere. The result is that higher levels of carbon now exist in the air than at any other time in the last 800,000 years. By 2050, carbon levels are expected to help raise the earth’s temperature between 3.5 and 7 degrees Fahrenheit, causing a series of worldwide, permanent events such as the melting of ice caps and flooding of coastal cities.

Because the Castello Aragonese vents are a preview of what oceans will look like in the next thirty years, Kolbert wants to examine them to understand better what will happen to marine environments and why. She enters the local marine biological station to observe the specimens they have in tanks. All the aquatic animals have suffered in some physiological way due to the high levels of carbon to which they’ve been exposed. Hall-Spencer explains that “some of these lower organisms … just got to tolerate what’s happening outside, and so they get pushed beyond their limits” (116).

The Castello Aragonese vents are a perfect example of what the world’s oceans will be like in a relatively short period. The closer one moves toward the vents, the higher the acidity of the water (i.e., the lower the pH level). Kolbert reasons that this area is “like having access to an underwater time machine” (116). Despite this notion, Hall-Spencer notes that it took some convincing to get his studies funded to test his theory; when it finally was, scientists found that even the most well-known and widespread marine life, like mussels and barnacles, were nowhere to be found near the vents.

Most alarming, according to Hall-Spencer, is that the marine ecosystem will begin to crash when pH levels hit 7.8, a level expected to be reached by the year 2100. Although some marine life will learn to thrive and survive, the acidification of the ocean will exterminate many other species, from the recognizable clownfish to other less recognizable animals essential to proper marine ecosystem functions. The main result, according to Ulf Riebesell, a biological oceanographer in Germany, is that “there is going to be a reduction in biodiversity” (120). In short, ocean acidification will have a significant enough impact to be considered a catastrophic event.

Kolbert explains why ocean acidification is so deadly, namely that it will affect basic ecological and physiological functions such as metabolism, change the amount of light passing through water, alter the availability of nitrogen and iron, and impact the level of noise in the water. It may also promote more rapid growth of algae, impact photosynthesis, and affect the way compounds are formed by dissolved metals, potentially causing toxicity.

Of all these possible effects, Kolbert is most concerned about the impact on marine calcifiers, small creatures who build shells or external skeletons. Starfish, clams, oysters, mollusks, and sea urchins are examples of calcifiers. To produce calcification, these animals “alter the chemistry of the water to, in effect, impose a chemistry of their own” (121). Ocean acidification destroys the efforts of these calcifiers by requiring the animals to expend more energy in an attempt to calcify, and once the water reaches corrosive acidic levels, the calcium carbonate of these marine creatures dissolves.

The carbon spewing from the Castello Aragonese vents has been doing so for centuries, and no calcifier has been able to adapt to the change in pH, or we would have proof of it. Ocean acidification will most likely result, therefore, in the extinction of many of these marine animals. Kolbert posits that this news is made worse by how quickly it is occurring, thanks to human damage being done daily to the environment.