If you could travel back 65 million years ago, you would be able to witness the fifth mass extinction on Earth. It was at that time that a major event -- likely the impact from a comet or giant meteor-- wiped out more than half of all life on Earth [source:Choi]. Among the life forms that died out were the dinosaurs.
The trilobyte, along with 95 percent of life on Earth, died out at the end of the Permian era.
As enormous as that extinction event was, an event 250 million years ago dwarfed it. The Permian extinction saw 95 percent of all marine life and nearly all land life die out [source: PBS]. The world might look very different today had this extinction not happened. Scientists believe enormous volcanic eruptions in what is now Asia caused this mass extinction.
Today, the Earth could be facing its next mass extinction. Depending upon which expert you ask, you may hear the extinction rate for species is 100 to 1,000 times greater than it normally should be [source: Connor]. Harvard biologist Edward O. Wilson once estimated that as many as 30,000 species go extinct every year.
Why are so many life forms dying out? Several factors could contribute to extinction, but one seems to dominate all others: human interference. Whether it comes in the form of hunting, destruction of habitat or introducing an alien species to a new environment, humans have made an enormous impact on life on Earth in general. The history of our meddling goes back 100,000 years, when humans first started to migrate out of Africa. And then really picked up around 10,000 years ago when humans developed agriculture.
Since that time, human activities have wiped out thousands of species of plants and animals. If the trend continues, we could see a mass extinction that could threaten our own survival.
It can be difficult to grasp how the extinction of a seemingly insignificant life form could impact the rest of the world. But it's true that one life form's disappearance could cause enormous problems for life in general.
Let's consider a fictional example. Imagine a lake teeming with life. There are fish and amphibians living in the lake, and insects on and around it. Reptiles, birds and mammals live around the lake and depend upon it, too. Now imagine that a species of insect at that lake dies out for some reason. The impact of this event could be catastrophic.
First, any other insects, fish or amphibians that fed upon the now-extinct insect would be affected. These creatures would either have to adapt by eating something else or would die out. Move one step further up the food chain and you'll see that it's a domino effect: The creatures that fed upon the animals lower on the food chain would see a decrease in their food supply.
Now imagine that scenario taking place across the entire world at varying levels of the food chain. According to Richard Leakey and Roger Lewin, authors of "The Sixth Extinction," we could lose half of all species onEarth by 2100. They point out that species extinction can happen even if we stop destructive habits now. Small populations may succumb to sudden events ranging from natural disasters to disease. But if we continue to clear away rainforests the situation will be even worse.
What can we do about it? It'll require humans to make some sacrifices. Decreasing our carbon footprint is a good start. Reducing the amount of meat we eat can also help since raising stock requires ranchers to clear land. Cutting back on destructive habits could save thousands of species over the next several decades. And it might just save us, too.
Learn more about biodiversity, ecology and extinction by following the links on the next page.
Humans are efficient killing machines. Back in 1978, two ecologists named Alwyn Gentry and Caraway Dodson documented 90 species of plants unique to the Centinela ridge in Ecuador. By the mid 1980s, farmers had cleared the ridge of the unique life to make space for crops. Those species are now lost forever.
The dodo bird is just one example of a species that went extinct due to human interference.
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