Scientists tell us that over the last half billion years, there have previously been 5 periods where massive numbers of the earth’s species became extinct.
The first great extinction occurred around 440 million years ago and the culprit is thought to have been climate change. 85 percent of marine animal species disappeared.
The second great extinction happened around 370 million years ago with many species of fish and 70% of marine invertebrates vanishing. Again, climate change is thought responsible.
245 million years ago, the third great extinction occurred; the largest of all. 95 percent of all animal species perished. Climate change may have played a role.
210 million years ago saw another mass extinction primarily consisting of marine creatures, but also some land animals. This was the fourth great extinction.
The fifth great extinction, the one most of us are familiar with, occurred around 65 million years when dinosaurs ruled the planet. This extinction was possibly caused by the impact of a comet or a massive volcanic explosion that interfered with earth’s ecosystem. Practically all dinosaur species disappeared and mammals emerged – and from those mammals, man evolved.
The sixth great extinction is now – we are witnessing it; in fact for the first time in this planet’s history, a single species is responsible – humans. It’s an achievement of the worst possible kind.
10,000 years ago, global human population was somewhere between 1 and 10 million people. We now number over 6.6 billion. Our seemingly endless thirst for resources means we are losing up to 27,000 species of plants, animals, insects, fungi, bacteria each year – just from tropical forest habitats.
The last 10 years has seen the overall number of threatened species increasing in all taxonomic groups according to the 2006 IUCN Red List.
While extinction is a normal part of evolution, the current extinction rate is anywhere from 1,000 to 10,000 times higher than at any time over the past 60 million years. That being the case, I don’t think this period of time being called the sixth great extinction is an exaggeration. Some say that the sixth great extinction will rival the third – 90-95% of all species will vanish over a very short period unless we dramatically change our ways.
On my walk through the bush this morning, I watched some little birds I’ve grown fond of that I haven’t been able to identify yet. They are as curious of me as I of them. They are very delicate, no bigger than my thumb, have a beautiful splash of red on their breast and a lovely song. Given they seem to be confined to a rather small area of scrub and favor certain plants, I wondered if they’ll still be around for much longer for me to marvel at.
Aside from the loss of beauty and diversity when a singles species becomes extinct, the disappearance of one species can be the trigger for the vanishing of many more that may be dependent upon it. We are also losing species useful for treating human illness; many we will never know of their therapeutic value as they are extinct already. Who knows, the cure and vaccination for cancer or AIDS that medicine has been searching so long for may disappear from our planet.. today.
Aggressive cancer is mindless – it only consumes, destroys the host and in the process destroys itself. Cancer and humanity have a lot in common.
Some further reading on the sixth great extinction and endangered species:
2006 IUCN Red List
The Sixth Extinction By Niles Eldredge
Earth Policy Institute
PBS Evolution library