The people behind the new Smithsonian Channel documentary Mass Extinction: Life at the Brink did a lot of scientific work travelling worldwide to bring into focus the subject of mass extinction, which happens when most of the planet's species die out on a rapid rate.

The Earth has seen five mass extinctions, two of which were featured in the hour long documentary using computer animation and other graphics. These were triggered by cataclysmic natural events and dramatic changes.

The Cretaceous-Tertiary extinction event also known as the K/T extinction, for instance, was known to have been trigged by the impact of a massive asteroid that caused the large-scale annihilation of the dinosaurs 66 million years ago, and "The Great Dying," is believed to have been caused by volcanic eruptions in Siberia about 252 million years ago.

Experts, however, believe that a sixth mass extinction is looming and it isn't caused by asteroids hurling from space or supervolcanoes. Scientists believe that the sixth mass extinction is manmade. Worse, people barely notice that this is already on the verge of happening.

One of the species highlighted by the documentary is the African lion. In 1950, their number is estimated to be between 400,000 and 500,000, but recent scientific estimate shows their number has declined by more than 90 percent with only 32,000 to 35,000 of these animals left.

The scarce number of the lions is primarily attributed to manmade activities with the International Union for Conservation of Nature blaming their decline on indiscriminate killing and depletion of their prey.

The case of the African lions is also reflected in other species that are similarly threatened due to man-made activities, said University of California-Berkeley biologist Anthony Barnosky, who was featured in the documentary.

"We have killed about 50 percent of the world's vertebrate wildlife in just the past 40 years," Barnosky said. "We've killed half the numbers of individuals. We've fished 90 percent of the fish out of the seas. So these are big things we're doing to the world."

Despite the grim situation, some scientists are still hopeful that things can be changed. In an interview with Salon, evolutionary biologist Sean Carroll, who hosts the documentary, said that while he thinks many of the Earth's species are threatened of being wiped out, they are not yet extinct which means that there is still room for rebound.

"What is doable, what is actionable is to strengthen, if not expand the reserves we already have," Carroll said. "Let's not wait for 160 countries to agree on something; let's act where people are both willing and able to do something. That's reserve by reserve, place by place across the world."

Mass Extinction: Life at the Brink will air at 8 p.m. ET on Sunday, Nov. 30 on the Smithsonian Channel. Watch the documentary preview shown:


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