Extinction is nothing new to planet Earth. In the context of life, the plants and animals that we share the planet with are always in a fragile balance.
Extinctions are usually caused by the occurance of natural phenomenon. This can result in a species being unable to survive, perhaps due to changing environmental conditions, resulting in severe disruption to the earth's ecosystem. Extinction can even be caused by superior competition amongst species. Those species with the greatest survival and reproductive skills will flourish. Their adversaries will struggle to survive and may be destined for extinction.
It also occurs due to human influences such as the habitat destruction we see in the tropical forests and coral reefs, hunting, industrial poisining and environmental pollution.
New species are created by speciation - the evolutionary process by which new biological species arise and thrive by exploiting an ecological niche. It is estimated that there are about 10 million species alive on the Earth today of which about 1.5 million have been discovered and given scientific names. It is also estimated that about 99.9% of all species that have ever lived are now extinct.
Complex life increased dramatacially during the Cambrian period with the appearance of animals such as trilobites, which began 540 million years ago. But the story of life on Earth since then has been punctuated by five mass extinctions which have been recorded in the fossil record. Here we see evidence that many species have disappeared in a relatively short period of geological time. These extinctions exceed the normal background extinction rate. In fact, on average as a result of these five great biological crises, over half of all living species became extinct.
Extinctions have been significantly assisted by geological activity such as the drifting of the continents or intense periods of volcanic activity, or in some cases, asteroid or comet strikes. Events like these can have catastrophic effects on climate change and ultimately, life on Earth. Only versatile species will likely survive such severe environmental changes. But in each extinction (so far) some species have slipped through to the other side. But their recovery as a sustainable species can take millions of years.
The web of life connects the smallest bacterium to the largest mammals. Are humans interfering with this web? Are we putting this web in peril with unknown and potentially disasterous consequences? Biologists estimate that species are being lost hundreds or even thousands of times faster than normal. Biologists regard this current era we live in as the planets sixth major extinction period. And its the first to be driven by one of the planets species, a relative newcomer on the scene - us!