Newsletter #171 The Sixth Wave: What Comes After Us?
Nieuwsbrief over natuur en wetenschap in Nederlands
Extinction Is Normal—Until It’s Not
Estimates vary widely, but there are between 1.5 and 2.1 million species of animals, plants, and fungi currently living on Earth. That’s less than one percent of the total number of species that have gone extinct, which certainly exceeds 200 million. As the word implies, extinction is perfectly normal. The lifespan of a species varies greatly—some last millions of years, others just a fraction of a year. On average, about 200 species go extinct every hundred years.
Still, extinction can spiral out of control. In the history of life on Earth, we now recognize five mass extinction events—periods in which over 70%, and in some cases even 90%, of all species perished. The culprits: volcanism, climate change, and meteor impacts. But according to many biologists, we are now in the midst of a sixth mass extinction, caused by humans.
Many new life forms emerged in relatively warm oceans during the early Cambrian and Ordovician periods, 541–443 million years ago. Paleontologists speak of a “Cambrian explosion” of life. Among those life forms were our earliest ancestors—precursors to chordates, and thus to all vertebrates. This rich marine life came to an end due to a sudden drop in atmospheric CO₂. The result: a prolonged ice age, falling sea levels, and the extinction of 85% of all species at the time. New life forms seized the opportunity—plants and forests grew on land, temperatures rose again, insects spread out, and the first vertebrates left the water.
But 75 million years later, disaster struck again: a new cold period lasting three million years, possibly triggered by meteor impacts, wiped out about 70% of species—especially those in shallow seas. Extinction wave number three was the biggest ever: 95% of all marine species disappeared 251 million years ago. Lava, ash clouds, and greenhouse gases spewed from massive volcanic regions in Siberia. A third of all insect species vanished. Temperatures soared to 40°C; 70% of land species died, and oceans acidified. Trilobites—arthropods resembling oversized woodlice—had ruled the seafloor for 250 million years, surviving two previous extinction waves, but now they too disappeared.
Fifty million years later, another bout of climate change devastated land animals, wiping out 80% of species, including many exotic reptiles such as flying pterosaurs and the marine plesiosaurs and ichthyosaurs. As always, this made space for new life—this time, dinosaurs. Their reign ended abruptly in the fifth and best-documented mass extinction, 66 million years ago. A comet impact, possibly combined with volcanism, caused prolonged darkness. All dinosaurs except birds died, creating an opening for mammals, including our own ancestors.
Some researchers believe we are already in the early stages of the sixth mass extinction. A very unusual one, because in the Anthropocene—the era in which humans, especially since the Industrial Revolution, exert a disproportionate impact on climate and the biosphere—things are accelerating rapidly. Around 30% of all species are currently at acute risk. And with ongoing habitat destruction, that number could rise quickly, even aside from the effects of human-driven climate change.
There are still people—including, notably, many politicians—who believe they could survive a sixth extinction. The comforting thought is: life after us will probably be fascinating.
Five tips to process our extinction:
Visit a natural history museum and look at the fossils that showcase the rich life that once was.
Read the book The Giant Salamander by Jelle Reumer, about the history of paleontology.( in dutch )
Watch episodes of The Future Is Wild, a 13-part series from 2002 that explores how life might continue without us.
Visit a (good) zoo and marvel at exotic life forms.
Even better: take a walk and be amazed by every plant, animal, and mushroom you see—we are more dependent on all living things around us than we think.
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