be devastated by environmental changes which occur too fast to adapt to, or which move outside the conditions that type of life needs to survive.
In the last 540 million years since the onset of the Cambrian Period, which corresponds roughly to the existence of complex life on the planet, there have been five major extinction events, in which not just species and genera but entire families of extant life were lost to the very last individual, vanishing forever. The most dramatic of these, at the end of the Permian period, marked the termination of 60% of existing animal families and more than 80% of all genera within surviving families. This doesn’t mean the other 40% were doing great; it just means that at least a few breeding individuals from one species of one genus of that family did not disappear, and so were not lost to the future. 12 The “Gaia” theory introduced by James Lovelock in the 1970’s asserts that life generally tends to make the world better for other life, and that feedbacks occur which tend to restore balances 13 . However, it is becoming clear that this can in fact go either way; biogeochemical impacts can either stabilize environments or drive them into instability, as stated by Peter Ward in his Medea hypothesis 14 (remember Medea in Greek mythology killed her children). So, in the past we see a pattern of greater and lesser extinction events with recovery periods in between. However, the greatest extinction events in history seem to have one thing in common: large CO 2 excursions which destabilize environments and wreck ecosystems, knocking back complex life to the smaller, tougher, short-lived and rapidly-reproducing species. Even the asteroid impact in the Yucatan 65 million years ago, which is widely seen as having killed off the dinosaurs, is now proving to have been associated with a long period of gradually rising CO2. 15 This is salient because a sixth planetary mass extinction now seems to be underway, with species extinctions occurring at 100 times the standard rate and rapidly accelerating, as populations are suffering heavy losses 16 . This is the anthropogenic extinction event, caused by a single species of primate and its chance encounter with gigatons of flammable fossils. It too is characterized by a rise in CO2, and one at least 10x more rapid than in any of the “big five” prior mass extinctions. 17 And therein, as Hamlet would say, “lies the rub!” TaaL: There have been a lot more than five mass extinction events on your Earth — many occurred before the emergence of complex life. One of the biggest was billions of years ago when a few species, largely cyanobacteria, started making poisonous gas which killed off most of the
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