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The extinction of an animal species occurs when the last individual member of that species dies. Although a species may be "extinct in the wild," the species is not considered extinct until every individual-regardless of location, captivity, or ability to breed-has perished.
Natural vs. Human-Caused Extinction
Most species became extinct as a result of natural causes. In some cases predators became more powerful and plentiful than the animals on which they preyed; in other cases, severe climate change made previously hospitable territory uninhabitable.
Some species, however, such as the passenger pigeon, became extinct due to man-made loss of habitat and over-hunting. Human-caused environmental issues are also creating severe challenges to a number of now-endangered or threatened species.
Mass Extinctions in Ancient Times
Endangered Species International estimates that 99.9% of the animals that ever existed on earth became extinct due to catastrophic events that occurred while the Earth was evolving. When such events cause animals to die, it's called a mass extinction. Earth has experienced five mass extinctions due to natural cataclysmic events:
- The Ordovician Mass Extinction occurred about 440 million years ago during the Paleozoic Era and was likely the result of continental drift and a subsequent two-phase climate change. The first part of this climate change was an ice age that obliterated species unable to adapt to the frigid temperatures. The second cataclysmic event occurred when the ice melted, flooding the oceans with water that lacked sufficient quantities of oxygen to sustain life. It's estimated that 85% of all species perished.
- The Devonian Mass Extinction that occurred about 375 million years ago has been attributed to several potential factors: diminished oxygen levels in the oceans, the rapid cooling of air temperatures, and possibly, volcanic eruptions and/or meteor strikes. Whatever the cause or causes, nearly 80% of all species-terrestrial and aquatic-were wiped out.
- The Permian Mass Extinction, also known as "The Great Dying," occurred about 250 million years ago and resulted in the extinction of 96% of species on the planet. Possible causes have been attributed to climate change, asteroid strikes, volcanic eruptions, and the subsequent rapid development of microbial life that flourished in methane/basalt-rich environments brought about by the release of gases and other elements into the atmosphere as a result of those volcanic activities and/or asteroid impacts.
- The Triassic-Jurassic Mass Extinction took place about 200 million years ago. Killing off about 50% of species, it was likely the culmination of a series of smaller extinction events that occurred over the course of the final 18 million years of the Triassic Period during the Mesozoic Era. Possible causes cited are volcanic activity along with its resulting basalt flooding, global climate change, and changing pH and sea levels in the oceans.
- The K-T Mass Extinction took place about 65 million years ago and resulted in the extinction of approximately 75% of all species. This extinction has been attributed to extreme meteor activity resulting in a phenomenon known as “impact winter” that drastically altered the climate of the Earth.
The Manmade Mass Extinction Crisis
“What is there to life if a man cannot hear the cry of a whippoorwill or the arguments of the frogs around a pond at night?”-Chief Seattle, 1854
While prior mass extinctions occurred long before recorded history, some scientists believe that a mass extinction is taking place right now. Biologists who believe Earth is undergoing a sixth mass extinction of both flora and fauna are raising the alarm.
While there have been no natural mass extinctions in the past half-billion years, now that human activities are having a quantifiable impact on the Earth, extinctions are occurring at an alarming rate. While some extinction occurs in nature, it is not in the large numbers being experienced today.
The rate of extinction due to natural causes is on average one to five species annually. With human activities such as the burning of fossil fuels and the destruction of habitats, however, we are losing plant, animal, and insect species at an alarmingly rapid rate.
Statistics from the UN Environment Programme (UNEP) estimate between 150 to 200 plant, insect, bird, and mammal species go extinct every day. Alarmingly, this rate is almost 1,000 times greater than the “natural” or “background” rate, and according to biologists, more cataclysmic than anything Earth has witnessed since dinosaurs disappeared nearly 65 million years ago.