Even in Paradise an occasional calamity can occur. Agate’s misfortune appeared in the form of a drought. To the west of the plain built by the ancient Niobrara River, the Rocky Mountains began to rise again. This renewed uplift, after millions of years of relative quiet, eventually led to an even drier climate and a replacement of the savanna with a landscape of unbroken grasslands from the mountains to the Mississippi River and beyond. Trees then could survive only on canyon slopes along the courses of the few large remaining rivers that crossed the plains. Those rivers flowed toward the central lowlands of North America, once an embayment of the Gulf of Mexico. This Mississippi Embayment, as it is called by geologists, extended as far north as the present location of Cairo, Illinois.
During the first rumbles of this upheaval there were occasional instabilities in the weather of the Great Plains. From the fossil evidence of Carnegie Hill, University Hill, and the _Stenomylus_ quarry, we can see that drought touched the land.
What happens when disaster stalks the land? That question, so pertinent to an understanding of fossil deposition at Agate, can be answered best by looking at the normal scheme of life. Animal populations are cyclic, increasing rapidly to near the highest numbers which can be supported on available food supplies. If times are good, animal populations can be quite high. If the food supply decreases, massive dieoffs result. Successive cycles of plenty and poverty then produce high populations followed by dieoffs.
The fossil evidence suggests that a prolonged drought occurred during the Golden Age at Agate, resulting in death everywhere. The vast numbers of rhino skeletons preserved at Carnegie Hill and University Hill provide paleontological evidence that the drought must have lasted for several years.
Climates change slowly, and there are wet and dry cycles. Every rancher and farmer discovers this when he plows new land during a wet cycle, for sooner or later drier years catch up with him. He expects the optimum to be the standard; but he is badly hurt during average times, and really suffers when the dry years come. It is the same with populations of wild animals. When the times are good and the grass and trees are lush, fat, and green, more of the young survive and the whole population flourishes. The plant-eaters expand their herds and the meat-eaters increase to keep up with the better food supply the plant-eaters provide. In each case the standards for survival are lowered, and the less than perfect can survive and in turn produce young of their own. But when the water fails and plants refuse to grow, the herbivores starve and the carnivore population in turn declines. Nature is indifferent—neither cruel nor kind. When times are bad every species is improved, for the strongest and most tenacious survive to reproduce themselves. There are benefits to hardship.