Five times in the history of Earth, life has been extinguished by cataclysmic events. In one of them, the K/T Extinction, a six-mile-wide asteroid wiped out the dinosaurs, and in the earlier Great Dying, fallout from massive volcanic eruptions annihilated 90 percent of the Earth’s species. Could it happen again? The Smithsonian Channel special "Mass Extinction: Life at the Brink" explains why and how these catastrophes occurred, and why humans now pose a greater threat to the planet than any geological disaster.

The documentary, premiering Nov. 30, explains how human behavior and mistreatment of the planet mirrors the aftereffects of past mass extinctions. It notes that overpopulation leads to loss of plant and animal habitats and extinction of species, and global warming releases greenhouse gases, which acidify the ocean. Scientists estimate that most of the coral reefs will disappear by 2070, and many species of plants and animals, now heading toward extinction at 12 times the normal rate, will disappear.

It's a chilling doomsday scenario, and according to evolutionary biologist Sean Carroll, who co-executive produced and appears in the special, "We should be very concerned. One of the main objectives of the film was to increase awareness of the serious of the present and future situation — not to scare people. There is enough of that from all sorts of sources."

A close up of marine life inside a tidal pool at the Fitzgerald Marine Reserve

A close-up of marine life inside a tidal pool at the Fitzgerald Marine Reserve in Moss Beach, Calif. (Photo: Tangled Bank Studios)

Nevertheless, he believes that we can learn a lot from the K/T and Great Dying events that may enable us to prevent man-induced global collapse. "What is very valuable about understanding these two past mass extinctions is that, even though they were caused by different triggers, they had similar effects in destroying habitat, altering the climate, and oceans. There is a very simple, but important lesson to take away: when environmental change is great enough, fast enough, and on a global scale, the whole planet is in jeopardy," Carroll says.

"If we continue with business as usual, growing our population, using more land, consuming natural resources, and harvesting animals, we will create a mass extinction within 100-200 years," he predicts. "The consequences will be loss of species, loss of food, and loss of a lot of services we get from nature, including water purification and pollination. It is also very likely that we will encounter new diseases from wild sources, and that existing diseases will move around the globe in new ways."

It is possible, however, to alter this dire trajectory if we act quickly, Carroll adds. "First, expand and strengthen land and marine reserves that hold a lot of species. That buys time. The next things will take longer: convert to using more renewable energy sources, make land use more efficient, and curb human population growth." He hopes the documentary will be a wake up call, and urges viewers to "act locally to support reserves, support organizations that are working on a larger scale. The probability of a large asteroid or volcanic event such as those in the film is very, very low," he reminds. "We are the asteroid."

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