Roughly 65 million years ago, the Chixulab boloid, a mountain of rock at least 60 miles across, struck the Earth.  The asteroid's origins are unknown, but fate had tied the destiny of our home, Earth, to that of the rock; when Chixulab struck, our Earth was changed, forever.

The Chixulab impact left several legacies: an enormous crater just off the coast of the Yucatan Peninsula, a layer of iridium-rich clay that forms the boundary between Mesozoic and Cenozoic in the Earth's rock strata, and the complete extinction of all of Earth's large animal species.

In short, Chixulab impact marked the end of the Mesozoic with the great Cretaceous-Tertiary (or KT) extinction.  The impact was by no means the only calamity to befall the creatures of Earth during the turbulent end of the Mesozoic, but it was the final straw, the coup de grace, ushering in a new era in the evolution of vertebrate life on Earth.  Many groups of organisms, the ammonoid cephalopods, the cycadeoidophyte plants, and the enantiornithian birds were completely obliterated by this, the greatest extinction in over 100 million years.  Others, like the great dinosaurs, pulled through with only a tiny fraction of their former diversity left intact, never to be regained.  The mammals, those furry, lactating therapsids, the creatures that had lost the original battle for ascendancy after the last great extinction to the dinosaurs, suddenly found all the doors open and diversification beckoning.

In the wake of the KT extinction, mammals exploded into dazzling array of giant forms.  Within 10 million years, almost all of the modern groups of mammals (and then some) had already appeared.  The mammals conquered the land, the water, and even the air (although the last remaining dinosaurs, the birds, are unquestionably dominant in at least the last of these niches).  The furry creatures spread to every continent and, only 65 million years after the Chixulab struck, have produced organisms of astonishing variety, from blue whales to shrews, from hyenas to humans.  The (non-avian) dinosaurs, once the largest land animals on the planet, have been reduced to mere stone and imagination.

But what if none of this history was true?

What if the rock had missed?

One can speculate.

(Text by Daniel Bensen)

(Picture by Stacey Burgess and Christopher Srnka)
"Once one dismisses
The rest of all possible worlds,
One finds that this is
The best of all possible worlds."---Leonard Bernstein, Candide

The History of the World


The Nature of Spec