In order for scientists to study the history of life on our planet, they require a relative scale so that they can place important events such as the first land vertebrates, or the first evidence of flowering plants in the perspective of geological time. Such a scale is provided by the science of geology. Geologists have subdivided the history of our planet into time intervals of varying duration. The largest periods of time are divided into Eons, an example is the Phanerozoic Eon (visible life), representing the period of geological time from approximately 550 million years ago to the present day. The Phanerozoic covers that period of time when fossils first become abundant, reflecting the obvious presence of life. Eons are divided into Eras, such as the Cenozoic Era that covers the last 65 million years (sometimes called the Age of Mammals). Eras are broken down into Sub-eras and further divided into Periods, hence well known sections of geological time such as the Jurassic and the Cretaceous. Periods are further sub-divided into Epochs. The last 10,000 years of geological time, roughly reflecting the adoption of sedentary farming and domestication of livestock by people, is known as the Holocene (recent time).
For much of the Holocene, the Earth's climate has been relatively stable. In fact, using information sources such as ice cores and micro-fossil studies, it seems that the Earth's climate has been more stable than during any other 10,000 year interval in at least the last 200,000 years or so. For much of this time, the human population has grown steadily. It is only in the last 200 years or so that the human population has grown dramatically. The growing demand for resources from the increasing human population, in conjunction with rapid climate change has been identified in a United Nations (UN) report due to be published this week, as causal factors in the dramatic decline of animal and plant species.
2010 - The Year of International Biodiversity
This year, 2010 is the year of international biodiversity as declared by the United Nations. Biodiversity is the variety of life on Earth, biodiversity is essential to support dynamic and robust ecosystems that ultimately provide our species with a sustainable environment, food, fuel, health and prosperity.
However, one of the conclusions in a United Nations (UN) report due to be released this week, is that animal and plant species are becoming extinct faster than ever before. A rapidly growing human population in combination with an increasing demand for natural resources represents a grave threat to nearly a third of all animal and plant species on the planet, the report states. The increasing economic activity and industrialisation of countries such as India, China and Brazil is adding to the environmental threats already generated by the developed western world, countries such as the United States and economic trading blocks such as the Euro zone.
Commentators are expecting this new report to be one of the frankest and most stark ever published by the UN. It will include conclusions that draw an explicit correlation between economic growth and extinction rates. For example, the faster and more dramatic the growth of economies, the quicker animal and plant species will be driven to extinction. The paper will point out that the extinction threat extends across all the main ecosystems of the planet, affecting organisms in environments as diverse as rain forests, grasslands, inshore environments and coral reefs.
With a relatively small portion of the known invertebrates formerly studied, it is alarming to read the predictions regarding extinction from the United Nations. It has been estimated that approximately 35% of all invertebrate species will be under extinction pressure by the end of the 21st Century. For animals, known as the mega fauna, some of the larger creatures in ecosystems, such as mammals and reptiles the situation is equally as bleak. In the UN funded report, an estimated 21% of all mammal species are threatened with extinction.
By the middle of this Century, the human population is estimated to have grown from today's level of approximately 6.8 billion to over 9 billion. That is an increase of 2.2 billion (32% increase in just forty years). Two thirds of the population will live in cities it has been predicted, in China alone over 400 new cities with populations greater than 1 million will have to built to accommodate this increasing population.
The increased demand for natural resources plus the adverse affect on global climate will have a dramatic impact on the diversity of life on Earth. Scientists are aware of a natural extinction rate, a sort of background rate of extinction. This background rate represents low levels of extinction as a result of evolution and adaptation plus some local or restricted climate/environmental change. The fossil record, although far from complete shows evidence of larger extinction events. There have been a number of extinction events recorded in the fossil record. For instance, many people may be aware of the Cretaceous mass extinction event that ended the reign of the dinosaurs, but a number of lesser extinction events are associated with the Cretaceous. Palaeontologists have identified five major mass extinctions in the Phanerozoic. The history of life on our planet has been punctuated by a series of mass extinctions, mass extinctions being defined in a number of ways, but normally they relate to the number of marine and terrestrial genera that die out in a relatively short period of geological time. Most scientists agree about the "big five" mass extinction events, but some scientists are arguing that the Holocene epoch should also be defined as a mass extinction event - the sixth mass extinction.
The Scale and Speed of Extinction
Although it is difficult to accurately assess the decline of fauna and flora, if mammals and birds are examined in isolation, an alarming picture is revealed. There are approximately 14,000 species of mammals and birds today. These types of animals are dying off at a rate approximately 10,000 times faster than the standard background extinction rate. The United Nations report uses data gathered from 120 countries, it concludes that the magnitude of damage to ecosystems is much bigger than previously reported. This UN report will show that no country has succeeded in halting the decline in biodiversity. Eighty-nine percent of those countries that submitted data had identified climate change as a major cause. For our species, the consequences could be dire. We humans are at the top of the food chain and very reliant on robust and dynamic ecosystems. The loss of a single species, the honey bee for instance, would have a significant and detrimental impact on our ability to produce food. Approximately, one third of all the vegetable and fruit crops grown on a commercial scale by humans, are pollinated by bees.
Given the current economic difficulties being experienced by many countries, it is likely that this report and its conclusions will not be not be given the prominence that it and the conclusions deserve. The fossil record in two million years time could show one of the most dramatic and rapid extinction events in the history of life on Earth.
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