Someone recently asked where the recent Tsunami disaster ranked in terms of the deadliest natural disasters. While it is certainly at or near the top of the worst in the history of humankind, it pales when compared to other events. Although our planet is (so far) the only known place hospitable enough to support and sustain life, there have been at least five times when much of that life was reduced to so much dead and decaying biomass.
There were at least five mass extinctions in earth's very distant path. Some suggest that we are, at best, on the cusp of the sixth extinction or, at worst, knee deep in it. Here's the scary part about that. In terms of geologic time, it is now widely believed that the Permian-Triassic mass extinction occurred over the course of about 10,000 years. That is considered "an instant" for 4.5 billion year old planet. But it is an unfathomably slow passage of time for human beings, meaning that we could be in the middle of a mass extinction and not even know it.
Ordovician-Silurian Extinction: 439 million years ago; Severe global cooling that led to an Ice Age that dramatically lowered sea levels. Two events suspected, the first from the shock of the sudden glaciation, the second from the shock of its sudden end. Toll: 25% of all marine families (a family can include a few or several thousand species); 60% of all marine genera (a class more extensive than a species, such as all four-legged animals as opposed to all four-legged mammals). Life on land, if any, very limited at the time.
Late Stage Devonian Extinction: 364 million years ago. Cause disputed; no generally accepted theories. Toll: 22% of all marine families; 57% of all marine genera.
Permian-Triassic Extinction: 251 million years ago. Several possible causes: comet or asteroid impact, but, unlike the more recent Cretaceous-Tertiary, no likely crater has been discovered; massive volcanic activity from the Siberian Traps depleting ocean oxygen levels; the former (comet or asteroid) may have caused the latter (Siberian Traps); also suspected massive release of frozen methane from the ocean. Toll: all life nearly extinguished; 90% to 95% of all marine species died.
End Stage Triassic Extinction: 214 million to 199 million years ago. Suspected cause is the creation of the present day Atlantic Ocean resulting from massive volcanism. Toll: 22% of all marine families, 52% of marine genera.
Cretaceous-Tertiary Boundary Extinction: 65 million years ago. Suspected causes: massive asteroid impact at present day Yucatan Peninsula and gulf of Mexico; massive volcanism at the Deccan Traps in present day India; possibly the former (asteroid) causing the latter (Deccan Traps). Toll: 16% of all marine families, 47% of all marine genera, 18% percent of all land vertebrates.
Each of the aforementioned extinctions took place during the Phanerozoic Eon, which began 543 million years ago and continues today. But most of earth's history came before that, in Precambrian time, which began 4.5 billion years ago.
#1. 650 million years ago. Believed by some to be earth's first mass extinction, killing off 70% of Precambrian flora and fauna, long before the development of hard-bodied and complex organisms.
#2. Vendian. 543 million to 523 million years ago. Before the rise of hard-bodied, complex organisms. Claimed creatures similar to today's jellyfish, sea worms and segmented worms.
#3. Jurassic. 206 million to 144 million years ago. (Two) More than 80% of marine bivalves and other shallow water species in the first. Stegosaurs and most sauropods did not survive the second.
#4. Oligocene. 33.7 million to 23.8 million years ago. Land mammals most affected.
#5. Late Miocene to Pleistiocene. As many as six separate events. The most recent, about 11,000 years ago, marked the end of mastodons, wooly mammoths, saber-toothed cats and large ground sloths.