The Sixth Extinction

The Sixth Extinction

In The Sixth Extinction, author Elizabeth Kolbert, a staff writer for the New Yorker magazine, weaves together interviews with scientists to discuss prehistoric extinctions, such as the end of the dinosaurs, and then to link them with current extinctions caused by people. Her thesis is that people are causing a sixth mass extinction, where the number of species sharply declines.

The Sixth Extinction
The Sixth Extinction

With the book’s format of interviews with scientists, I lost the big picture of the five mass extinctions that came before us. This isn’t a big deal, but the book’s title of six extinctions, might lead some readers to ask what the first five were. For those interested, the wikipedia article on mass extinctions has a much clearer summary of the five mass extinctions than I found in The Sixth Extinction.

Kolbert does a excellent job portraying current extinctions caused by man.

Farmers are clearing Amazon rainforest to raise crops, while preserving the rainforest on half their land. Scientists have found that the resulting islands of rainforest can’t sustain the number of species that larger tracts can. A smaller population can be endangered by an accident of nature, while a larger population would survive the loss of an individual nest or food source. Plants and animals can depend on other species for food or shelter, so the loss of one species can lead to the loss of others.

We are transporting animals and diseases to areas where the local flora and fauna have no resistance. Bats in New York and New England are dying off due to a fungus imported to the US. My experience in California is that the coast live oak (quercus agrifolia), a California native plant, is being devastated by phytophthora ramorum, a pathogen probably imported from Europe in nursery stock. The pathogen kills three species of California native oaks, and so far scientists haven’t found any members of the three species that resist the pathogen.

By burning fossil fuels, we are rapidly raising the temperature of the earth. In response, some plants and animals might move to cooler microclimates that are higher elevation or farther from the equator, but the high rate of change makes it more harder for plants and animals to move fast enough.

Burning fossil fuels releases carbon dioxide, and some of this carbon dioxide is being sequestered in the ocean, causing the ocean to become more acidic. As the ocean becomes more acidic, this interferes with the ability of coral to build reefs. Coral forms calcium carbonate from free calcium and carbonate, but this takes energy, and the ability of the coral to drive the chemical reaction drops as acidity increases. The scientist visited by the author estimates that unless the rate of ocean acidification is changed, all coral reefs will cease to grow in 50 years. Since natural forces like fish eating coral reduce coral, the amount of coral would shrink if building new coral is blocked. Examining coral near volcanic vents that raise the acidity of the nearby ocean confirms that coral lose their ability to form as acidity increases.

In the final chapter Kolbert discusses conservation research and how man is trying to keep species alive. People might not survive the changes set in motion, or perhaps human ingenuity will figure a way out.

I especially valued Kolbert’s clear explanation of why ocean acidification from rising carbon dioxide will lead to the demise of coral reefs, both the chemistry and the empirical study of sea life around volcanic vents that confirms the science. Each story of a scientist and the subject of his or her study was very well-written. But I found the connecting of the stories into a book to be lacking, both in explaining the previous five mass extinctions and the final chapter on where do we go from here. Or perhaps there are no good solutions on where we go from here, and that’s the author’s point.


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I enjoy travel, art, food, photography, nature, California native plants, history, and yoga. I am a retired software engineer. The gravatar is a Nuttall's woodpecker that visited our backyard.

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