The Sixth Extinction

“The sixth mass extinction has begun” – that’s a headline I came across a few weeks ago when browsing through articles posted by members of the Zero Waste group on Facebook. I felt both intrigued and frightened by this title, but I was not quite sure what it meant. The idea of mass extinction is easy to understand and imagine even for someone who is not a scientist. But why sixth extinction? I have decided to find out more and this is how I discovered “The Sixth Extinction. An unnatural history” – a Pulitzer winning book written by an American journalist Elizabeth Kolbert.

“The sixth extinction. An unnatural history.” by Elizabeth Kolbert (Polish edition)

Five mass extinction events…

As you can easily guess, mass extinction refers to a sudden and global decrease in the number of species living on Earth. So far our planet has witnessed five such extinction events: Ordovician-Silurian, Late Devonian, Permian-Triassic and Cretaceous-Paleogene. Even if you are unfamiliar with the name, you must have heard about the fifth extinction event, as a result of which most of dinosaurs perished. This one was caused by a giant comet or an asteroid. Other factors contributing to these past events were volcanic activity, as well as sea level and climate changes. Each mass extinction event caused a great number of species living on the planet to disappear. At the same time, an event that meant extinction to one species, could become a huge opportunity to another. The creatures that somehow managed to find an ecological niche and survive the major disaster, received a unique opportunity to evolve and dominate in the post-apocalyptic world.

… and the sixth one

So what does the sixth extinction refer to? According to some scientists, it is the ongoing mass extinction event, caused mostly by human activity. The epoch in the planet history characterized by significant human impact on the Earth’s environment has been called Anthropocene. There is a number of experts who claim that human activity and the trace it leaves on Earth are indeed comparable to the force of an asteroid. One of these scientists is Jan Zalasiewicz whose research and works are described in Elizabeth Kolbert’s book:

“Zalasiewicz is convinced that even a moderately competent stratigrapher will, at the distance of a hundred million years or so, be able to tell that something extraordinary happened at the moment in time that counts for us as today. This is the case even though a hundred million years from now, all that we consider to be the great works of man—the sculptures and the libraries, the monuments and the museums, the cities and the factories—will be compressed into a layer of sediment not much thicker than a cigarette paper”.

Elizabeth Kolbert’s travels

“The Sixth Extinction” is a reportage in which the author describes her travels to places where she can find some clear evidence of the ongoing crisis. She visits scientific centres and speaks to experts from the US, Scotland, New Zealand, Brazil and Iceland. With her own eyes she sees how fast species are disappearing these days: coral reef animals, birds, bats, frogs, rhinos and many others. Their extinction is caused by many very complex factors but all the threads lead to the most probable contributor – the mankind. Directly or indirectly, consciously or not – people are hugely responsible for this state of things. Some species disappear because of poaching, but many others – due to human-caused global warming or ocean acidification.

“Roughly one-third of the CO2 that humans have so far pumped into the air has been absorbed by the oceans. This comes to a stunning 150 billions metric tons. As with most aspects of the Anthropocene, though, it’s not only the scale of the transfer, but also the speed that’s significant. A useful (though admittedly imperfect) comparison can be made to alcohol. Just as it makes a big difference to your blood chemistry whether you take a month to go through a six-pack or an hour, it makes a big difference to marine chemistry whether carbon dioxide is added over a course of a million years or a hundred. To the oceans, as to the human liver, rate matters”.

Another aspect of human activity leading to the ongoing extinction is travelling. Crossing oceans and continents has never been so easy but hardly anyone thinks about the chaos it causes in most ecosystems. Many species – like bats described by Kolbert in her book – perish due to diseases that were unknown before – brought to them recently from distant continents.

“During any given twenty-four-hour period, it is estimated that ten thousand different species are being moved around the world just in ballast water. Thus a single supertanker (or, for that matter, a jet passenger) can undo millions of years of geographic separation. Anthony Ricciardi, a specialist in introduced species at McGill University, has dubbed the current reshuffling of the earth’s biota a “mass invasion event.” It is, he has written, “without precedent” in the planet’s history.”

An era of giant rats

Undoubtedly, the conclusions drawn in the book are rather depressing. To cheer you up I can add that Elizabeth Kolbert has also included a few more optimistic threads in her book.  On her way, she has met many great people – scientists and volunteers – who undertake numerous (and often heroic) actions to keep the endangered species alive. Will they be able to protect our planet’s biodiversity? Or maybe it is too late already and we are heading for a (un)natural disaster that we ourselves have caused?

According to some scientists, chances are that humans are on the list of species that will disappear – or at least lose their dominance on the planet – as a result of the sixth extinction. One of them claims that the most probably our species will be replaced by rats – animals with superior survival skills. He also explains that after the possible apocalypsis they will evolve to much greater size than their ancestors.

If you want to find out more about giant rats – and not only – I highly recommend you reach for Kolbert’s book. The author has really done a great job, carrying out her insightful investigation, talking to experts from all the corners of the globe and searching for empirical evidence for the existing state of things.  It required a great deal of sacrifice on her side: she dived in ice-cold seas, explored caves full of bat guano and undertook a number of other equally unpleasant actions. Her book, in spite of its difficult subject and frequently scientific tone, is really fascinating and brilliantly written with a certain dose of humour.



  1. Zainteresowałaś mnie bardzo książką, aż sprawdzę, czy jest w mojej bibliotece. Takie książki zazwyczaj wpędzają mnie w przygnębienie, ale jeśli piszesz, że jest odrobina humoru, to spróbuję 🙂

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