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         Mass extinction: The wipe-out of many species of organisms in a short period of time. In the past, there have been five major mass extintions: The Cambrian extinction, the Devonian mass extinction, the Permian mass extinction, the Triassic mass extinction, and the Cretaceous mass extinction. Though there is thought to be mass extinctions in the Archaean Eon when life was only starting to develop, there were no hard bodied organisms to supply sufficient evidence of these events. Most mass extinctions are caused by either sudden changes in the environment or astronomical impacts on Earth like meteors or comets. Every mass extinction that had happened so far killed at least 50% of life and tested the natural abilities of adaptation and evolution.

          The first recorded mass extinction, the Cambrian extinction, also known as the Cambrian Explosion, occurred at about 440 million years ago. The Cambrian extinction killed thousands of marine species. Scientists think the cause of the Cambrian mass extinction may be the effects of sudden climate change, more specifically, sudden global cooling. The Cambrian mass extinction led way to the Ordovian Period.

          The second major mass extinction occurred during the Devonian Period about 370 million years ago. The most accepted theory of this mass extinction is the theory that a sudden climate change is responsible for the death toll. Not much is known about this extinction.

           The third mass extinction, the Permian extinction, was the greatest mass extinction so far, killing about 95% of life. There are two accepted theories about the cause of this massive extinction, the first being a result of climate change due to the movement of tectonic plates. The second theory is that an impact from space similar to the end-Cretaceous extinction may have been the cause.

          The fourth mass extinction occured in the Triassic period, shortly after the evolution of dinosaurs and mammals. Scientists are having problems identifying the cause so it is hard to pinpoint the reason why many of these organisms went extinct.

          The fifth mass extinction, the cretaceous extinction, is the most well known mass extinction. Also known as the K-T extinction, this mass extinction wiped out the dinosaurs. The most accepted theory about this extinction is that a meteor hit and caused a series of events such as hyper canes (super hurricanes) and a rain of fireballs.                                                                  

          These terrible events are the five major mass extinctions of the past, but now there is a theory about a sixth mass extinction occuring today. This current mass extinction theory is accepted by about 75% of scientist and is the first mass extinction to have a biologic cause:humans. This is the fastest mass extinction so far, with about four species going extinct every hour. It is belived that 50% of life will be extinct by 2050, and only eleven of one-hundred thirty-five bird species will survive to the twenty-first century. Many people may blame global warming by the rising carbon dioxide levels, but this is just a fraction of the cause. The real problems are glocal warming, deforestation, the spread of agriculture, overhunting, environmental pollution, and overpopulation. Biologist believe the carrying capacity of humans scientists predict agriculture can support is about 13 billion people and the population will rise to 8 billion by 2020.

          Humans must band together in unity, side-by-side, to protect the next generation, prove those who believe it is too late to solve this crisis wrong, and save our little, blue planet. For more info on the sixth mass extinction, go here.

The first picture is from here, and the second image here