Lonesome George is a large, mud-loving Pinta tortoise (Geochelone elephantopus abingdoni), living out his long life in the Galapagos Islands. In 1971, George was found alone on Pinta Island and taken to the Charles Darwin Research Station, where scientists theorized that he was the last of his subspecies on the planet. When he dies, his genetic lineage will disappear forever. Unfortunately, his companionless circumstances are not unique. In fact, we are in the midst of the Sixth Great Extinction, an event characterized by the loss of between 17,000 and 100,000 species each year.
WHAT ABOUT THE FIRST FIVE?
The first extinction, named the Ordovician-Silurian extinction, occurred around 440 million years ago (m.y.a.). Scientists hypothesize that both a southerly continental drift that led to a drastic decrease in temperatures and radiation caused by the collapse of a massive star known as a hyper nova may have caused this massive loss of diversity on Earth.
The second extinction was the Late Devonian. Approximately 370 m.y.a., there was a sharp decrease in marine reef biodiversity. Many factors may have played a part in the Late Devonian extinction, but the causes remain mostly unknown.
Around 245 million years ago, during the Permian-Triassic extinction event, marine species died off to such an extent that oceanic reefs did not exist anywhere on the planet for ten million years. A combination of factors, including volcanic eruptions, climate change and a possible meteorite impact, made this the largest historical extinction event.
In the Triassic-Jurassic extinction, circa 210 m.y.a., 48 percent of genera vanished from the earth, including 80 percent of quadrupeds and half of all marine invertebrates. Although the causes of this event are unknown, scientists believe that volcanic activity contributed to extinctions.
The Cretaceous-Paleogene extinction event, circa 65 m.y.a. (formerly known as the Cretaceous-Tertiary or K-T), is best known for the extinction of the dinosaurs and nearly all large animal species. During this event, temperatures increased by as much as 57 degrees Fahrenheit (32 degrees Celsius) and sea levels rose as much as three hundred meters.
During each extinction event, between 50 and 95 percent of the planet’s life was lost, resulting in dramatically changed biotic characteristics. Generally, ten million years pass before biodiversity reaches pre-event levels.
THE MOST CATASTROPHIC
The Sixth, however, may be the most catastrophic in history. It is estimated that half of all plants, animals and birds on the planet will die off before 2100. This extinction is the first to occur during the existence of homo sapiens, and it simultaneously began 100,000 years ago, a date that corresponds with the beginnings of our dispersion from Africa. In fact, this extinction is almost exclusively human driven.
There are many contributing factors to the Sixth Great Extinction; today, destruction of habitat, introduction of alien species and pollution claim the most species. Extinctions are also caused by overexploitation of species for consumption, collection and trade, agricultural monoculture, human-induced climate change, nitrogen loss in soil and oceanic acidification as a result of a warming climate, and urbanization leading to sedimentation and soil erosion. Growing human populations have led to increased demand for natural resources, and with a current world population of more than seven billion people, our demands, many of which require environmentally damaging practices to fulfill, will continue to grow.
WHY SHOULD I CARE?
Since most people probably cannot name a single recently extinct species, does it really matter to the human race whether we save biodiversity or let much of it disappear into the history books? The answer is a very strong and profound, Yes. By failing to recognize the importance of biodiversity, we may be assuring the demise of our own human species, as well as the destruction of most other species on Earth. We need biodiversity.
Biodiversity provides climate stability, nutritiously varied and abundant foods, medicines, clean water, pollination of crops, disease-control, cultural diversity, environmental knowledge, food-chain stability, and oxygen.
The world’s leading scientists suggest that conservation measures, sustainable development, stabilization of the human population and the support of environmentally responsible economic development will be essential in halting the extinction crisis. Read more at Izilwane, and join us in our quest to nurture an appreciation for biodiversity by becoming an eco-reporter.
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Celâl Sengör, A.M., Atayman, Saniye and Sinan Özeren. 2008. A scale of greatness and causal classification of mass extinctions: Implications for mechanisms. PNAS September 9, 2008. Vol. 105 no. 36.
Eldredge, N. 2001 “The SixthExtinction.” ActionBioscience.org http://www.actionbioscience.org/newfrontiers/eldredge2.html
Leakey, R. and Lewin, R. 1996. The Sixth Extinction: Patterns of life and the future of humankind. First Anchor Books.
Whitty, J. 2010. “Gone: Mass Extinction and the Hazards of Earth’s Vanishing Biodiversity.” Mother Jones. Accessed September 10, 2010 at: http://motherjones.com/environment/2007/05/gone?page=1
Wilson, E.O. 2010, “Only Humans Can Halt the Worst Wave of Extinction Since the Dinosaurs Died.” Accessed July 15, 2010 at:http://raysweb.net/specialplaces/pages/wilson.html
– Photos by Jonmikel and Kathryn Pardo