Perhaps the most striking thing about the Evolving Planet exhibit at the Field Museum is the clear delineations between sections. Each of those transitional stages marked on the floor in bold letters on a blood red background is entitled Mass Extinction. These extinction-level events are characterized by a sharp decline in the number of species alive on the planet in a relatively short amount of time. Thus far there have been five events that we can identify, and we might well be on our way to a sixth, according to some prognosticators, but does it really matter?
The oldest agreed upon extinction event was the Ordovician-Silurian which occurred nearly 450 million years ago. Many a trilobite family was destroyed during this natural disaster, perhaps triggered by an ice age and fall in CO2, wreaking havoc on shallow seas where much of life congregated.
The second of the great extinction-level events is known as the Late Devonian extinction and happened about 365 million years back, though it may have extended over as little as a half million years on up to fifteen million years. It may have actually been a number of smaller extinction-level events happening in series and having an overall massive devastating effect. This event, or combination of events, greatly lowered levels of oxygen in the oceans of the world and primarily destroyed marine life.
The third is called the Permian-Triassic because it marks the transition between those geologic periods, occurring just over 250 million years ago. These events, by the way, are all named in this same fashion. Now this baby was a real killer, knocking out about ninety-six percent of the world’s species. It is known that this particular event was the most difficult from which the planet had to recover.
The Triassic-Jurassic event, the fourth, took place about 200 million years ago. Massive volcanic eruptions combined with gradual climate change at the end of the Triassic period are the most likely combined causes of this extinction-level event. This event was fairly short by some measures, taking place over about ten thousand years. For those who know a bit about plate tectonics, this also happened to coincide with the beginning of when the super-continent Pangaea started to break up, giving the world’s landmasses today’s familiar shapes.
Event number five was not the biggest, but might have been the most spectacular. The Cretaceous-Tertiary extinction event happened about 65.5 million years back, and is now widely believed to have been caused by a combination of massive asteroid impacts and vast amounts of volcanic activity. The lack of sunlight, and great amounts of airborne particles, made this devastating to both land creatures and plant life, the latter having done fairly well through the other four major extinction-level events. This one spelled the end for dinosaurs, except for the birds, of course, and mostly only semi-aquatic or burrowing mammals and marsupials managed to make it through the transition, along with the abundant smaller marine life.
So when some tree-hugging doom-crier starts spewing some crap about how the water is going to rise and flood everything, or how the ozone layer will disappear and the atmosphere will become inhabitable, leaving the Earth a nearly lifeless husk, just go ahead and chuckle. We can all be secure in the knowledge that the planet has survived far worse than anything we could do to it. What matter then if the billions of bi-pedal organisms that damage it are wiped out and no longer around to not care about the Earth a second time? Other species will take our place when the world bounces back and can once again support life, unless we do a better job than the previous five catastrophes. In which case, Go Team!
If you wish to learn more about the Evolving Planet exhibit at the Field Museum visit http://www.fieldmuseum.org/evolvingplanet/exhibition.asp or call the museum at 312-922-9410