Extinctions crop up over the millennia with disturbing frequency; even mass extinction events pepper the history of the planet every 65 million years or so. But when it comes to the causes of these phenomena (whether it's a sea-level shift, an asteroid strike, a volcano eruption or a nearby supernova), scientists have a hard time settling on just one cause for one event.
Take the extinction of many species of megafauna near the onset of the Holocene (the geologic period that we still live in today). Scientists have different theories for why it happened. Some experts believe a wild climate shift caused radical habitat alterations. Others pin the problem on human intervention: Maybe human advancements led to overhunting and habitat destruction. Or perhaps the problem was that the bipedal interlopers (and any animals they carted around the world with them) unwittingly acted as pathogen vectors, carrying new diseases to animals without pre-existing immunities.
Often a combination of factors is suspected of triggering certain extinction events. Take the recent plummet in the world's population of saiga antelope. Native to different regions of the former Soviet Union and once numbering more than a million, this endearingly gawky looking little antelope species was poached to the brink of extinction after the dissolution of the crumbling empire in 1991. As of 2010, only about 81,000 remain. But at the start of summer 2010 -- and in the span of just two weeks -- that number dropped dramatically to 67,000 animals [source: Platt].
The party to blame that time wasn't poachers but a parasite that causes pasteurellosis. The infection's associated bacterium is just fine as gut flora in healthy antelopes, but for an animal with a suppressed immune system, it's a big problem. The antelope struck down by the infection were likely malnourished since the region they lived in had just gone through a colder-than-average winter and a warmer-than-average spring, seasonal upsets that likely affected food supplies.
Rooting out the Crucial Causes of Extinction
Pasteurellosis may have killed more than 10,000 saiga antelope, but technically, people may still be to blame for the species' plight. Some scientists are dubbing the current era the planet's sixth mass extinction, and they're pointing their fingers back at us as the root cause since even small changes to the planet's delicate ecosystem can domino into catastrophe.
But as we try to take in the scope of how badly we've treated the planet, let's avoid the usual buzzwords like "unsustainable agriculture," "overharvesting" and "pollution," and really step into the shoes of the planet's plant and animal population. They're forced to maneuver a veritable minefield of threats in order to survive, dancing around (or more aptly, struggling to adapt to) deadly hazards every step of the way.
Vast landfills tainted by plastics and heavy metals, along with massive streams of contaminated wastewater, pollute both soil and waterways. Huge oil spills cloud ocean waters and mammoth stretches of pavement coat once viable land. Airplanes and high-rise buildings present aerial obstacles, and farms and family homes suck up habitat. Speaking of commercial farming operations, they waste water and leach dangerous pesticides into the environment. Houses are hotbeds of chemicals as well, containing everything from cleaning products to beauty supplies. Global warming cooks oceans and lands alike, and dams and reservoirs block migration routes in lakes and streams. Ocean traffic and road traffic both contribute to dangerous levels of light pollution, noise pollution and death through collisions. Slash-and-burn practices destroy forest ecosystems faster than we can discover and study the untold numbers of species they contain, and strip mining wipes out entire mountain ranges. Invasive species threaten native populations, and the spread of hyperviral pathogens grows easier by the decade.
The basic point is this: It took an enormous asteroid slamming into the planet at fantastic speeds to alter the Earth enough to accelerate the last major extinction event. This time around, we might be that asteroid.
Biological anthropologists seek to understand the differences within and between human populations. Learn more about biological anthropology.
Related HowStuffWorks Articles
- Why do small changes in the Earth's temperature have a big impact?
- How do you clean up an oil spill?
- Are my bath habits destroying marine ecology?
- Can we ever replace plastic?
- Could we clean up the Great Pacific Garbage Patch?
- Can we replant the planet's rainforests?
- If I plant trees in my yard, will it offset global warming?
- If the polar ice caps melted, how much would the oceans rise?
- Has the Earth reached its carrying capacity?
- Are we at the beginning of the end of Western civilization?
- What life forms on Earth are close to extinction?
- When will life on Earth end?
More Great Links
- "An epidemic of extinctions: Decimation of life on earth." The Independent. May 16, 2008. http://www.independent.co.uk/environment/nature/an-epidemic-of-extinctions-decimation-of-life-on-earth-829325.html
- "Are We Pushing Earth's Environmental Tipping Points?" Scientific American. March 19, 2010. http://www.scientificamerican.com/podcast/episode.cfm?id=are-we-pushing-the-earths-environme-10-03-19
- "Ask the Experts: DeeAnn Reeder on bat research" Bucknell University. Feb. 4, 2010. http://www.bucknell.edu/x58280.xml
- Britt, Robert Roy. "Pleistocene Park Could Solve Mystery of Mammoth's Extinction." Live Science. May 6, 2005. (8/25/2010) http://www.livescience.com/animals/050506_mammoth_park.html
- Carey, Bjorn. "The Perils of Being Huge: Why Large Creatures Go Extinct." Live Science. July 18, 2006. (8/25/2010) http://www.livescience.com/animals/060718_big_animals.html
- "Earth In Midst Of Sixth Mass Extinction: 50% Of All Species Disappearing." Science Daily. Oct. 21, 2008. (8/25/2010) http://www.sciencedaily.com/releases/2008/10/081020171454.htm
- Franklin, Jonathan. "Frog, Lizard Extinctions Caused by Climate, Not Fungus, Study Suggests." National Geographic News. April 17, 2007. http://news.nationalgeographic.com/news/2007/04/070417-frogs-lizards.html
- "Mini Frog, Among Smallest in the World Discovered." Live Science. August 25, 2010. (8/25/2010) http://www.livescience.com/animals/pea-sized-frog-discovered-100825.html
- Platt, John. "Epidemic kills 12,000 critically endangered antelopes." Scientific American. June 10, 2010. (8/25/2010) http://www.scientificamerican.com/blog/post.cfm?id=epidemic-kills-12000-critically-end-2010-06-01
- Roach, John. "Mystery Undersea Extinction Cycle Discovered." National Geographic News. March 9, 2005. (8/25/2010) http://news.nationalgeographic.com/news/2005/03/0309_050309_extinctions.html
- "Species disappearing at an alarming rate, report says." MSNBC. Nov. 17, 2004. (8/25/2010) http://www.msnbc.msn.com/id/6502368/
- "The Great Dying." NASA. 2002. (8/25/2010) http://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/
- The IUCN Red List of Threatened Species. http://www.iucnredlist.org/
- The Story of Stuff Web site. (8/25/2010) http://www.storyofstuff.com/
- Wilson, Edward and Peter, Francis. "Biodiversity, Volume 1." National Academy of Sciences and the Smithsonian Institution. March 16, 1998. (8/25/2010) http://books.google.com/books?id=MkUrAAAAYAAJ&lpg=PA21&ots=AyXtCAQcps&dq=what's%20worse%20loss%20of%20plant%20diversity%20or%20loss%20of%20animal%20diversity%3F&lr&pg=PP1#v=onepage&q&f=false
- Zimmer, Carl. "Carriers of Extinction." Discover Magazine. July 1995. (8/25/2010) http://discovermagazine.com/1995/jul/carriersofextinc540/?searchterm=reasons%20for%20extinctions