The truth is, scientists don’t know how many species of plants, animals, fungi, and bacteria exist on Earth. The most recent estimate put that number at 2 billion, and that will most likely change at some point.
One thing we do know: The western black rhinoceros, the Tasmanian tiger, and the woolly mammoth are among the creatures whose populations at one point dwindled to zero, and it’s possible that species extinction is happening a thousand times more quickly because of humans.
The last living Rabb's fringe-limbed tree frog died in 2016 at Atlanta Zoo. The now-extinct Panamanian frog species was discovered in the wild in 2005, and just two years later no more of the frogs could be found.
PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
Extinction happens when environmental factors or evolutionary problems cause a species to die out. The disappearance of species from Earth is ongoing, and rates have varied over time. A quarter of mammals is at risk of extinction, according to IUCN Red List estimates.
To some extent, extinction is natural. Changes to habitats and poor reproductive trends are among the factors that can make a species’ death rate higher than its birth rate for long enough that eventually, none are left.
Humans also cause other species to become extinct by hunting, overharvesting, introducing invasive species to the wild, polluting, and changing wetlands and forests to croplands and urban areas. Even the rapid growth of the human population is causing extinction by ruining natural habitats.
Among the most famous species driven to extinction by humans is the dodo, a bird that primarily lived in the island nation of Mauritius and was popularised by its appearance in Lewis Carroll’s book “Alice’s Adventures in Wonderland.” Dodos were first mentioned by Dutch sailors in the late 16th century and last seen in 1662 after having been hunted to extinction. Passenger pigeons, billions of which frequently blanketed North American skies when Europeans arrived on the continent, went extinct when the last one died at the Cincinnati Zoo in 1914.
PHOTO ARK: SAVING SPECIES ONE PHOTO AT A TIME
Many of the species that keep our planet diverse and healthy are rapidly disappearing in the wild. That’s why National Geographic and photographer Joel Sartore are building a Photo Ark, documenting every species in captivity, including those at risk of extinction.
Six mass extinctions
Fossils show that there have been five previous periods of history when an unusually high number of extinctions occurred in what are known as mass extinctions. Most of the Earth’s species went extinct roughly 266 million to 252 million years ago in the Permian extinction.
Those losses, however, also paved the way for dinosaurs to evolve into existence, as mass extinctions create a chance for new species to emerge. Dinosaurs met their end about 65 million years ago in another mass extinction at the end of the Cretaceous period. A large crater off of Mexico’s Yucatán Peninsula suggests that an asteroid most likely struck there. Scientists believe that volcanic eruptions in India caused global warming that also may have contributed to the mass extinction.
Scientists are debating whether Earth is now in the midst of a sixth mass extinction. If so, it may be the fastest one ever with a rate of 1,000 to 10,000 times the baseline extinction rate of one to five species per year. Humans are largely responsible for the striking trend. Scientists believe that pollution, land clearing, and overfishing might drive half of the planet’s existing land and marine species to extinction by 2100.
Slowly increasing surface temperatures caused by heightened levels of greenhouse gases likely will cause many species to move toward the Earth’s poles and higher up into the mountains to stay in habitats with the same climates. But not all species will be able to adapt quickly enough to stave off extinction and many are expected to perish.
What can we do about it?
Using fewer fossil fuels by lowering the thermostat, driving less frequently, and recycling is one good way to slow the rate of extinctions. Eating less meat and avoiding products, like ivory, that are made from threatened species also can make a difference. At home, securing garbage in locked cans, reducing water usage, and refraining from using herbicides and pesticides can protect local wildlife.