| It is scientifically accepted that our planet Earth is about 4,540,000,000 years old and the Universe we inhabit about 13,750,000,000 years old.
|
|
|
Extinction is a fundamental, essential element of evolution through natural selection as postulated by Charles Darwin – species are predestined to die out. Humans have a relatively short life span and are usually unable to watch evolution in its process. When Darwin published his theory it was a revolutionary scientific concept contrary to the accepted beliefs of Victorian England still bound in mystical creation.
The very idea that humans had anthropoid ancestors stemming from apes was a great stumbling block in the acceptance of Darwin’s theory. The proud Victorians were reluctant to believe that their ancestors originated from apes and the press of the day lampooned and denigrated the idea.
|
 |
An astonishing and depressing fact is that 140 years after Charles Darwin published his book “On the Origin of Species By Means of Natural Selection” a great number of people throughout the world still believe in a mystical creation for humans and the environment around them.
It is all the more surprising that over half of US citizens, in the richest and most ‘advanced’ country of the world, do not believe in evolution according to a poll by CBS in 2006. Although most other ‘Western’ countries do not show such a heavy bias3, it is remarkable just how many people still adhere to discredited dogma.
Religious beliefs obviously determine attitudes toward science to the point of irrationality. It seems that poverty and lack of higher education underpin these religious attitudes in the US and Europe so it can be surmised that global belief in evolution is quite low.
This is a daunting thought considering the power, financial and technical, which lies with countries still predominantly non-secular. Nations which feel they are answerable to a ‘higher’ force cannot be relied upon to react rationally in any crisis.
The position of the US as a Super Power is rather unnerving considering the extent of its non-scientific orientation. People with strong spiritual convictions can be considered weak links in any chain of command as they might have a conflict of interest.
|
Overview of Extinction
|
Even if we take it for granted most of the time, we are part of a very complex and inter-dependent world. Although we may know that a species has become extinct there are probably a number of causes, often acting together over a long time period. Extinctions caused by sudden catastrophic events are certainly very rare and 'normally' extinction takes place after many hundreds, if not thousands, of years before the negative conditions required are reached.
Over 99% of all species that ever lived are now extinct.
At least five major and eight relatively minor mass extinctions have already occurred since life began on Earth about 4 billion years ago: Botomanian, Dresbachian, Cambrian, Ordovician, Silurian, Devonian, Mid Carboniferous, Permian, Triassic, Jurassic, K/T Cretaceous-Triassic, Eocene and Pliocene. All of these mass extinctions paved the way for new taxa to dominate the environment. The famous demise of the dinosaurs allowed birds and mammals to flourish and become the dominant vertebrates over the last 65 million years. More recent waves of extinction in the Eocene and Pliocene are considered as blips in the background level of extinction, however important they were for the fauna affected. The case for a present mass extinction, perhaps to be called the "Anthropocene", is discussed under "Hologene Extinctions".
Research into all scientific fields has multiplied during the last 50 years and basic knowledge about the world we live in has increased enormously.
We now know extinction occurs at a continuous if uneven rate. It has been calculated that the general background level of extinction known from the fossil record is about one species per million species per year. As we now have an estimated one and three-quarter million species (counting all organisms such as insects, bacteria, and fungi, not just the large vertebrates we are most familiar with) we should expect an average extinction loss of 1.75 species per year.
However, although there is some agreement about the number of known species there is controversy about the estimated number of possible species which have not yet been discovered and described (see World Species). If one accepts an estimation of 8 to 9 million world species we should expect to loose between eight and nine species each year. It should be noted that these higher figures are often based on extrapolations of creatures living in specific biodiversity transects which may or may not be accurate reflections of other areas not so intensively studied, or on assumptions about unproven biological relationships.
The background or underlying rate of extinction seems to have decreased from about ten species per million to about two today, which is more in line with the figure mentioned first. This may be due to the ageing of the earth as cataclysmic events become rarer or not so pronounced. Alternatively, species may have become more resistant to the motors of extinction and live for longer. During the known mass extinction events between one third and one half of all animal life was wiped. Before 600 Ma we have little fossil evidence because creatures were soft bodied, but in all probability mass extinctions took place in the preceeding 3 billion years since the start of the Archean eon too.
Biodiversity seems to have increased over the course of time. This would imply that species have occupied new ecological niches and, at the same time, become more dependent on the stability of their food web.
|
Extinctions help in the generation of new species. Our geological past has great extinctions where many of the living species died out within a relatively short space of time, geologically speaking. The extinction of the Dinosaurs, about 65 million years ago, did not happen overnight but took perhaps several thousand years and was the result of several contiguous unrelated events, including perhaps asteroid impact, volcanism and sea level change, all contributing to climate change. As the Dinosaurs died out other species were able to speciate and radiate, filling the available habitat.
This is a small dinosaur Microraptor gui which lived 125.5-130 million years ago, long before the K/T boundary extinctions.
Extinctions are taking place all the time as species become unable to adapt to a changing environment or succumb to pathogenic infestation or direct competition. New species able to exploit food resources or replace other animals will prosper. Except on the very rare occasions when natural events like volcanic eruptions or tsunamis occur, this process of extinction takes a long time and would not be noticeable during a human life span.
|
The most important factors governing the survival of any species is the supply of food and water: If only one of these is missing life cannot exist at all. Habitats are selected by species because they supply these essentials through a food web. Species are dependent on this web and rely, to a greater or lesser degree according to the food specialisation, on the continued survival of the members of that web. Previously the food web was considered to have a pyramid like structure and was called the food chain, but it is now recognised to have a much more complex interdependent structure. Major change in this food web is ultimately the cause of most extinctions.
Every habitat is an individual ecosystem reliant upon the continuation of intrinsic diverse elements. There are a number of external factors which potentially could upset the equilibrium of an ecosystem and thereby cause a species to become extinct. We call these extinction motors, but they rarely act alone and usually operate in tandem with or are caused by others.
Extinction motors
Solar and galactic influences
Climate change
Sea level change
Continental drift
Volcanic activity
Asteroid impact
Pathogens
Other species
|
|
