by Shane L. Larson
At the end of the Cretaceous Period, 65 million years ago, a rock from space roughly 10 kilometers in diameter crashed into the Earth. The result of that impact was an energy release equivalent to 100 million megatons of TNT and the excavation of a 180 kilometer diameter crater on the edge of the Yucatan Peninsula, known as the Chicxulub Impact Crater. The outcome of that single astronomical event was the Cretaceous-Tertiary extinction event, in which nearly 75% of all plant and animal species that inhabited the planet died off, vanished from the face of the Earth forever.
This is not the only extinction in the Earth’s history, it is simply the most recent. Based on fossil evidence, over 98% of all species that have ever been documented are extinct, exterminated from the Earth by the long slow march of history. Looking around the Earth today, the planet is rippling with life, every nook and cranny of every ecosystem filled with plants, animals and microbes. One can hardly believe that only 65 million years ago, a blink of an eye in geologic history, life on this planet had been decimated. But biological systems are designed to evolve, trading entire species for mutation experiments in adaptability.
By all accounts, the Chicxulub impact was a serious event. The deposition of 100 million megatons of TNT in equivalent energy into the environment had serious ramifications for the design of the Earth’s biosphere: the reptilian lifeforms that had ruled the planet for millions of years were snuffed out and replaced by a new experiment that has since had millions of years to expand and flourish. We are living in a between time, going about our lifey-business until the next catastrophe pushes Nature toward a new design. Fortunately for us, huge depositions of energy like the Chicxulub event are rare. Right?
The prospects of another Chicxulub Impact Event are terrifying to ponder, but remote in prospect. Based on the historical occurence of impact events on the Earth and the Moon, it seems the likelihood of a similar impact is roughly one per hundred million years. But the Laws of Nature are broad in scope and aspect; it may be that all the Earth’s biosphere cares about is energy in any form, whether is comes in the shape of a rare astrophysical impact event, or some other seemingly benign trend.
Consider the loss in Arctic sea ice. There is a concerted worldwide effort to monitor the change in ice levels in the Arctic and Antarctic, and the results are disturbing to many scientists. Why? One recent study reported the loss of 1400 cubic kilometers of the (formerly) permanent Arctic ice (Kwok & Cunningham, GRL 37, L20501 ). For a 1 kilometer thick ice sheet, this is an area roughly the size of Salt Lake City, seemingly small in comparison to the entire Arctic. But how much energy did it take to melt 1400 cubic kilometers of ice? An energy equivalent of 100 million megatons of TNT — the energy that was released in the Chicxulub impact. Worldwide, there are ice melts of this magnitude in the glaciers, on the Greenland ice sheet, and on the West Antarctic Ice Sheet. Worldwide, the warming of the coldest areas of the planet are indicative of energy shifts equivalent to many times that of the Chicxulub Impact.
By physical accounts, the Chicxulub impact made a small perturbation to the Earth, but in doing so wiped out the dinosaurs, creatures that had inhabited the Earth for hundreds of millions of years, unchallenged in their superiority and adaptability. They are now all gone. But Nature is adaptable in design, and replaced the failed ecosystem of the dinosaurs with a new one, the one we inhabit today. Now humans are making similar subtle perturbations to the world. Nature will have no qualms about wiping us from the face of the planet, a failed iteration in the 4 billion year old experiment in evolution. The system is designed to discard the old, and replace it with something more adaptable. Who will our successors be? What traits will Nature design to make them survive the new ecosystem we are creating? Will intelligence be one of them? Perhaps, perhaps not. The robustness of Nature’s evolutionary machinery is awesome in scope, but ruthless in operation. Looking at humans as one cog in the great wheel of evolution, it is unclear that Nature will decide that this thing that we call intelligence is a superior trait for survivability.