Approaching a Mass Extinction?

The Golden Toad, native to Costa Rica, is believed to have gone extinct in 2007. A new study suggests Earth may be on the verge of mass extinction. Credit: Wikimedia

Three Things You Should Know:

1) During the past couple hundred years, scientists have documented the extinction of more than 700 animal species — and this is probably just a small fraction of the total number of modern plant and animal extinctions.

2) By comparing the rate of extinction today to previous rates revealed by fossil records, scientists project that the Earth may soon experience “mass extinction”, the likes of which have only occurred five other times in about 540 million years.

3) Human activities like hunting, deforestation, agricultural development, and pollution have caused many modern extinctions and climate change also poses a significant threat. Depending on the rate of global warming, researchers predict 20-35 percent of today’s species may be lost forever during the next several centuries.

The Debrief:

Several news outlets ran a story earlier this week about research that finds the rate of plant and animal extinctions around the world today is much higher than during most periods of history. In fact, the research says extinctions are currently so common that Earth may be on the verge of a “mass extinction.”

Paleontologists have only documented five other periods of mass extinction in history, when fossil clues indicate that as much as 75 percent of species were wiped out over periods of a few thousand to a couple million years.

Scientists today have recorded a staggering number of extinctions in just the past two centuries — including more than 700 mammals, reptiles, and bird species. But because biologists know they haven’t come anywhere close to discovering all the species on Earth, that figure is probably just a tiny fraction of the real number of extinctions that are taking place. With that in mind, researchers at the University of California at Berkeley compared the current extinction rate to rates recorded in the fossil record. They found that what is happening these days is completely out of the ordinary.


In particular, the rates at which mammals, birds, and reptiles are going extinct today is as fast — and in some cases, much faster — than what led to the five major extinctions in the past. The study is published in the March 3 issue of Nature.

To date, only a small percentage of species have been lost in modern times, which means this era doesn’t yet qualify as a “mass extinction.” But what is important, write the study’s authors, is how rapid the recent extinctions appear to be taking place. If the rate of species loss continues, and if many critically endangered species, like southern bluefin tuna or mountain gorillas, disappear, they say it would “propel the world to a state of mass extinction.”

In other words, we’re not experiencing this kind of event right now…but we may be on the cusp.

Why This Science Matters:

Past mass extinction events had a number of likely causes. Periods of dramatic climate change, when the planet was quickly warming or cooling, have been implicated in many of these events. In addition, rising concentrations of greenhouse gases, including carbon dioxide (CO2), changed the ocean’s chemistry so drastically at times that most species couldn’t survive. And asteroid collisions probably instigated at least one of the mass extinctions.

We’re not expecting another asteroid collision anytime soon, but some of the other triggers — climbing temperatures and ocean acidification — are taking place today.

Of course, there is one very big difference between prior times of mass extinctions, and now: us. Humans weren’t around during any of the previous extinctions, so it would be tempting to think that today’s extinctions are unrelated to human behavior. But according to this study and other research, that clearly isn’t the case.

Pollution, hunting, clear-cutting vast swaths of rainforest; all these human activities have contributed to the loss of hundreds of species. Recent climate change, which is likely caused in part by burning fossil fuels, have also begun to put pressure on species the world over, and further climate change will likely put even more species at risk.

In fact, computer models predict that if global warming continues in the coming decades, between 20 and 35 percent of the planet’s species could be headed for extinction within just 40 years.