Graph modified after Verisimilus
The graph shows the percentage of marine animals becoming extinct. The five major events are:
March 23, 2013
Of all species that have existed on Earth, 99.9 percent are now extinct. Many of them perished in five cataclysmic events. The classical “Big Five” mass extinctions identified by Raup and Sepkoski are widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous. According to a recent poll, seven out of ten biologists think we are currently in the throes of a sixth mass extinction. Some say it could wipe out as many as 90 percent of all species living today. Other scientists dispute such dire projections.
“If you look at the fossil record, it is just littered with dead bodies from past catastrophes,” observes University of Washington paleontologist Peter Ward. Ward says that only one extinction in Earth’s past was caused by an asteroid impact – the event 65 million years ago that ended the age of the dinosaurs. All the rest, he claims, were caused by global warming.
Ward’s study, Under a Green Sky, explores extinctions in Earth’s past and predicts extinctions to come in the future. Ward demonstrates that the ancient past is not just of academic concern. Everyone has heard about how an asteroid did in the dinosaurs, and NASA and other agencies now track Near Earth objects.
Unfortunately, we may not be protecting ourselves against the likeliest cause of our species’ demise. Ward explains how those extinctions happened, and then applies those chilling lessons to the modern day: expect drought, superstorms, poison–belching oceans, mass extinction of much life, and sickly green skies.
The significant points Ward stresses are geologically rapid climate change has been the underlying cause of most great “extinction” events. Those events have been, observed Harvard evolutionary biologist Stephen Gould, major drivers of evolution.
Drastic climate change has not always been gradual; there is solid empirical evidence of catastrophic warming events taking place in centuries, perhaps even decades. The impact of atmospheric warming is most potent in its modification of ocean chemistry and of circulating currents; warming inevitably leads to non-mixing anoxic dead seas.
We are already in the middle, not the beginning, of an anthropogenic global warming, caused by agriculture and deforestation, which began some 10,000 years ago but which is now accelerating exponentially; though the earliest wave of anthropogenic warming has been stabilizing and beneficial to human development, it appears to have the potential for catastrophic effects within a lifetime or two.
Looking at the ancient evidence, Ward notes that ice caps began to shrink. “Melting all the ice caps causes a 75-meter increase in sea level will remove every coastal city on our planet.” It will also cover earth’s most productive farmland, the author warns, adding, “It will happen if we do not somehow control CO2 rise in the atmosphere.”
An analysis of the geological record of the Earth’s sea level, carried out by scientists at Princeton and Harvard universities supports Ward using a novel statistical approach that reveals the planet’s polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level.
According to the analysis, an additional 2 degrees of global warming could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term sea level rise. This rise would inundate low-lying coastal areas where hundreds of millions of people now reside. It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the U.S. East Coast, much of Bangladesh, and most of the Netherlands, unless unprecedented and expensive coastal protection were undertaken. And while the researchers’ findings indicate that such a rise would likely take centuries to complete, if emissions of greenhouse gases are not abated, the planet could be committed during this century to a level of warming sufficient to trigger this outcome.
- Is Earth Undergoing a 6th Mass Extinction? –“99.9% of all Past Species Extinct” (dailygalaxy.com)
- Mass extinction 200 million years ago has lessons for today (blogs.courier-journal.com)
- Another link between CO2 and mass extinctions of species (phys.org)
- Comet, Not Asteroid, Killed Dinosaurs in Mass Extinction Event (scienceworldreport.com)
- Megavolcanoes tied to pre-dinosaur mass extinction (eurekalert.org)
- Before dinosaurs’ era, volcanic eruptions triggered mass extinction (eurekalert.org)