Biological mass extinctions on planet Earth

Abstract

Both gradual and catastrophic events have been involved on the mass extinction events on the planet Earth. Although the greatest mass extinction with currently identified fossil remains was the Great Dying, the greatest of all mass extinctions on planet Earth should have been the Great Oxygenation Event (GOE), assuming that no life was present at the time of the Moon formation. In general, and excluding the unique GOE, the climate changes have been the most common causes of mass extinctions on Earth. A comet or large meteorite may cause mass extinctions not only on land, but also on the oceans. Indeed, a bolide of a few kilometers in diameter may release as much energy as several million nuclear bombs. On the other hand, localized oceanic extinctions may arise from special events like the quasi-periodic climate pattern known as �El Niño� Southern Oscillation (ENSO). Such events may have also a significant impact on terrestrial ecosystems, causing extinctions of plants and animals. Up to five major mass extinctions have been recorded in the last 540 million years, killing an average of 50% or more of all living species at the time of the event. The fossil record suggests that mass extinctions on the planet Earth occur about every 26 million years. This is a very serious matter indeed, because if such hypothesis holds true, it is just a matter of time before the Earth is hit by a huge bolide with catastrophic consequences. It is revealing to note that 99% of all species that ever lived on planet Earth are now extinct. That includes all our hominid ancestors. Besides other considerations and factors, the human activity is significantly disrupting the planet Earth ecosystems. It should be also taken into account that now �for the first time�, the human activity can also cause mass extinctions. In fact, the current rate of species extinctions is shocking; estimated at about 10,000 times the past average as deduced from the fossil record. The conclusion is clear and definitive: our only chance to survive is to colonize the cosmos. On the other hand, we must take care of many possible causes of extinction, but particularly on those derived from the synergistic effects of human activities, in order to take action to prevent the global contamination and warming of the planet Earth. In a practical way, halting and reversing such trends requires significant changes not only in industries in general, but also in human behavior in particular (food wastefulness, unnecessary travel and pleasure tourism, fashion squandering, etc), in order to effectively reduce both the contamination and the emissions of the greenhouse gases. Obviously, that requires a global economic and marketing change. A pacific revolution involving a global social and political agreement is needed. It should be also clear that each and every one of us has the responsibility to take care of our planet Earth.