The Sixth Mass Extinction

Here’s how many people, if they are not in denial about it, view the current environmental crisis: global warming has begun, weather will become more extreme, and the changes in temperature will impact agriculture, the habitability of sea coasts, and the survival of some species. The last item—species extinction—sits like an afterthought in such a summary. The description minimizes the prospect that we are probably entering the sixth of the planet’s massive extinctions.

The first five mass extinctions took place over the last half billion years as the results of sustained volcanic eruptions, large meteors, and ice ages. They lasted for millions of years. Today, though, in the popular imagination, they seem like little more than fantastical events far in our past that are pictured occasionally in magazines and science fiction movies.

dinosaurs and meteors

A picturesque extinction. Dinosaurs looking alarmed. (

The current mass extinction is man-made. Called the Holocene extinction for the present geological epoch that began in 10,000 BC, it results from the steady increase in human numbers and, in modern times, from global warming, environmental destruction (rain forests, for example), overfishing, pollution, and the movement of invasive species and diseases around the world. It seems likely that each of these plagues is just getting warmed up.

The first five extinctions saw the loss of more than half of existing species, most often around 70% or more (apart from microbes). The most recent mass extinction, about 65 million years ago, has gained some  reknown. A six-mile-wide meteor hit the Yucutan peninsula and its impact on the climate wiped out the dinosaurs as well as an estimated 75 percent of other species. (For comparison, the normal rate of extinction is a few percent annually, as species evolve into new ones or succumb to competition or normal environmental change.)

timeline of mass extinction

The first five mass extinctions. The dinosaurs came into their own after the Triassic-Jurassic extinction and went out with the Cretaceous-Paleogene one.

The severity of the current, sixth, extinction is debated. According to Wikipedia, estimates run between 100 and 1000 times greater than the normal extinction rate. Ten years ago, E.O. Wilson famously predicted the loss of half of the current species 100 years from now. The exact rate aside, the losses have already cut across the organic spectrum. Amphibians, including frogs and toads; bird populations; fish species; invertebrates, mostly insects; plant species—all have declined. Mammals are vulnerable because they are dependent on plants and other animals down the food chain. In part because humans live almost everywhere on the globe, our species is not likely to be pressed to extinction anytime soon. But we can’t know the long-term impact of the next several decades’  addition of billions more humans and their demands for water, minerals, meat, and cars.

No matter whether the current extinction turns out to be a major one or only a middling one, its severity will earn it a place among the turning points for life on the planet. The chain of earthly life that is billions of years long has been tested in the past by meteors and volcanoes. It’s painful to think that it will be tested this time by one of its own.

The Meteor and The Asteroid: A Reminder

What surprised me about the Russian meteor news last week is that scientists and the public knew plenty about the large asteroid that missed Earth by 17,000 miles but nothing about the 7,000-ton meteor coming right at us the same day at the unimaginable speed of 40,000 miles per hour (really, try to imagine 40,000 mph).

The rock that missed us--

The rock that missed us–

and the one that didn't.

and the one that didn’t.

The New York Times reported one scientist saying that the meteor was impossible to see with a telescope because it had approached from the daylight side. But this meteor had previously been circling the sun in its own orbit and its path could, it seems to me, have been anticipated. Later news, of course, was filled with plans for renewed efforts to spot such intruders in the future.

The larger message, though, is that when it comes to dangerous disruptions in our environment, scientists and others are often looking in the wrong direction. We head off one obvious consequence but miss the long-term effects of a slower moving one. One problem makes headlines, solutions gain momentum, but a related problem grows in the shadows.

For example, we value agriculture and industrialization so much that we pay little or no attention to the species that have become reduced or extinct from the loss of their habitats. We’ve expected global warming to raise temperatures slightly; we did not expect it to contribute to more violent storms. The 2004 tsunami in Indonesia killed 230,000 people; there were plenty of tsunami detectors in the Pacific Ocean where tsunamis are frequent but none in the Indian Ocean where this rare one struck. Disease control teams respond quickly to dangerous viruses, but a few people get on airplanes and the damage is difficult to control.

Alert for SARS--

Alert for SARS–

but not for the tsunami.

but not for the tsunami.

Our lapses in anticipating disasters aren’t surprising. We are fallible. And when our fallibility joins together with the sheer power of nature to clobber us, the result is humbling. It’s unlikely that an apocalypse will wipe us all out any time soon; we are, after all, a global species.  But we may well be driven into decline by combinations of our mistakes and nature’s realities: earthquakes, limited fresh water, the loss of habitable places, the dysfunctions of our cultures, surges in population.