Evolution

But the rain itself brought further devastation. It was full of sulfuric acid from the ice clouds, and the impact had injected thin clouds of toxic metals into the atmosphere, metals that now rained out. Nickel alone reached twice the threshold of toxicity for plants. Runoff water washed substances like mercury, antimony, and arsenic out of the soils, concentrating them in lakes and rivers.

And so on. For years, every raindrop would be poisoned.

The great rain washed out the dust and ash. All over the world, a fine layer of blackened clay was laid down, a band of darkness that would forever show up as a punctuation in the sedimentary rocks of the future — a boundary clay, one day to be studied by Joan Useb and her mother, the last remnant of a biosphere.

After months of dark the sun showed, at last, through the planet-girdling layers of dust and ash. But it was only a pinprick, shedding barely any heat on the frozen land; there would be no more than a murky twilight for another year.

The returning sun illuminated a skeletal landscape.

Tropical plants, if not burned, had been killed by the sudden cold. Any surviving dinosaurs were succumbing to hunger and cold, their bones quickly stripped of flesh by the surviving predators. But here and there living things moved in the ash: insects like ants and cockroaches and beetles, snails, frogs, salamanders, turtles, lizards, snakes, crocodiles — creatures that had been able to hide in mud or in deep water — and many, many mammals. Their furry bodies and habits of burrowing into the shelter of the ground were protecting them from the worst of the cold. Their indiscriminate eating habits helped as well.

It was as if the world ran with rats.

And even now the survivors were breeding. Even now, despite the cold and the shortage of food, in the absence of their ancient predators, their numbers were increasing. Even now the blind scalpels of evolution took raw material adapted for a vanished world and cut and shaped it for the conditions of the new.

Alone, the female euoplocephalus stumbled through the endless cold, seeking the rough forage she needed.

She was of a species of ankylosaur. Her body was ten meters long and, before her slow starvation had begun, she had weighed as much as six tons. Her armor was bone: plates of it set in the skin of her back, neck, tail, flanks, and head. Even her eyelids were plates of bone. The plates were woven into a layer of tough ligaments, making the great carapace flexible, if heavy. Her long tail terminated in a fused mass of bone. Once she had used this club to lame a young male tyrannosaur, her greatest triumph — not that she was able to remember it; all that armor had left little room, and little need, for a large brain.

Though geologically sudden, the great death unfolding across the planet was not instant in the consciousness of those who endured it. For days, weeks, months, many of the doomed clung to life — even dinosaurs.

Relatively speaking, the euoplos had been well-equipped to survive the end of the world. Their massive bulk, great strength, and heavy armor — together with a fortunate placing beneath a thick layer of cloud close to the bank of a river — had enabled a few of her kind to endure the first few horrific hours. She had survived droughts before; she ought to withstand this unexpected calamity. All she had to do was keep moving and fend off the predators.

And so, wandering the freezing Earth, she sought food. And found hardly any.

One by one her companions had fallen away, until the euoplo was alone.

But, in a final irony, she had endured one last mating, from a male now dead; and she found herself heavy with eggs.

In this new world, a land of ice and blackness and a lid of gray-black sky, the euoplo had been unable to find the ancestral rookeries. So she had constructed a nest of her own as best she could, from the bare, cinder-strewn floor of what used to be a rich forest. She had laid her eggs, lowing, setting them carefully in a neat spiral on the ground. Euoplos were not attentive mothers; six-ton tanks were not well equipped to deliver tender loving care. But the euoplo had stayed close to her nest, defending it from the predators.

Perhaps, despite the cold, the eggs might have hatched. Perhaps some of the young could have survived the great chill; of all the dinosaurs, perhaps it was an ankylosaur who might have endured best in the new, harsher world to come.

But the stinging rain had leached away the nutrients the euoplo’s body needed to manufacture successful eggs. Some of them had been laid with shells so thick no infant could ever break out, others were so thin they were broken as soon as she produced them. And then the rain began to damage the eggs directly, the grimy downpour etching away their protective surfaces.