"Three coolers full of bad beer," Walls murmured, "divided by three desperate sailors. Take the rest of mine if you want it. I'm so full now I'll be pissing like a freight train for days to come."

"You only got one left."

"Drink it."

"Then what'll we do?"

Walls yawned. "Sober up, I guess."

"Unless," Berry said to McNiel, "you wanna haul yourself down to Stinktown and bring back another cooler. I'm so looking forward to spending more time up here, trying to get shitfaced on three-two."

McNiel actually appeared to consider it for a moment. Then he cast a doubtful eye skyward. "Be getting on towards dark by the time we got it back here." He slightly emphasized the pronoun.

Berry sighed profoundly. "Christ, I hate this place. We might as well've stayed on the ship."

"Bite your tongue," said Walls. "Yesterday, you couldn't get ashore fast enough."

"Yesterday, I just wanted to get away from the chief. Him and that new butthead jay-gee we got now."

McNiel took aim with an imaginary rifle of his own. "What do you need dinosaurs for, when fuzz-faced lieutenants infest the prehistoric world?"

Berry scowled. He had fine, curly blonde hair atop a round, smooth face. It was almost a baby face, and the scowl made him look merely petulant rather than formidable. "That little bastard won't let up on the chief about that tool belt I lost over the side. So the chief won't let up on me. It ain't like I deliberately threw the damn thing overboard. Christ Awmighty, court-martial me for losing Navy property, but stop scolding me like I was a little kid. You'd think it was the end of the world because a lousy tool belt fell overboard."

"Sounds to me," Walls said, "like the jay-gee's worried about the butterfly effect."

"The what?"

"It's one of the paradoxes everybody used to worry about." Walls raised himself on one elbow. "I thought they stopped giving the paradox lecture when they stopped making everybody wear those spacesuit-looking getups, but maybe young lieutenants still have to listen to it. Ah, God, those suits. Count us lucky, boys. Even after they stopped wearing the things, it used to be that if a guy so much as farted, he had to write it up in triplicate. Damage-assessment specialists'd carry on about how one poot was going to unbalance the whole Paleozoic ecosphere. Anyway, maybe the jay-gee just saw the same science-fiction show I did. It was about this guy who travels to the dinosaur age and accidentally steps on a butterfly. The butterfly's an important link in a chain of events stretching across the eons. It's the ancestor of thousands of generations of butterflies that would've been food for animals that would've been food for other animals, et cetera. On and on, right up until it's our own distant ancestors who're going hungry and dying off before they're supposed to. When the guy gets back to his own time, everything's different. Because of that butterfly, that one little death millions of years earlier, history's been changed, Hitler won World War Two or became a painter or something. Maybe the South won the Civil War, I don't know."

"That'd sure settle your hash, Walls."

"Wouldn't it, though? So, let's say the jay-gee saw that show. Then he hears you've dropped your tool belt into the bay, and he thinks, Omigod, what if it brains the one fish that's going to give rise to amphibians and reptiles and us? He thinks, This dumb rating's maybe erased the dinosaurs and cavemen, Egypt and Rome, the Bible, everything."

Berry's scowl had deepened and his complexion had reddened as he listened, improving his resemblance to a cranky toddler. "Somebody oughta tell him the future already exists. It can't be changed."

"How do you know? Who says it can't be changed?"

"The scientists. Physics."

Walls laughed. "Now what the hell do you know about physics? For that matter, what do physicists know? They used to say time travel was impossible, and had the figures to prove it. Then they found a hole in time big enough to steer a ship through. Zap, and here we are, having the time of our lives four hundred million years before we're even born!"

"Well, notice," said Berry, "we ain't having to do it dressed up like spacemen. And I don't think the scientists worry much about killing something they shouldn't. They ain't been making pets out of the specimens they collect."

"Maybe," said Walls, "it's like the lottery. Only one ticket in ten million matters. The rest are just waste paper. The odds must be a trillion to one somebody's actually going to catch and cut up the animal that's the linchpin of our entire history."

McNiel scratched his jaw thoughtfully. "Maybe the animals that're part of your chain of events can't get killed before they're supposed to. Like, they have to survive."

"Sounds too much like predestination to me."

"I have got to remember every word of this," Berry said with fine sarcasm, "so the next time the chief gets after me, I can talk rings around him."

Nobody spoke again for several minutes. Berry stood glowering at the sea. Walls hummed. McNiel stretched out on his side and drank the last beer. When he had finished, he began tracing a pattern on the ground with his finger. He said, "This isn't even real dirt."

"What?" Berry looked wonderingly at him.

"This place--this time, it doesn't even have real dirt." McNiel took a pinch of grit between his fingertips, rolled it there for a moment, flicked it away. "It's just sand. No organic matter in it at all." He saw the look Berry was giving him. "I was just thinking, there's probably not more'n a ton of decent topsoil in the whole world right now."

"This is the age of mud and slime," Berry said, "and I can't believe I volunteered to come to it because I thought it'd be exciting."

"That does it." Walls sat up, stretched, and swung his legs over the edge of the slab. "If you're about to launch into a whole new cycle of grousing, I'm heading back. Coming, Mac?"

"I'm not sure I can get up from here."

After a while, however, they noticed that the tide was coming in and how the shadows had deepened and lengthened across the valley. It really was time to go. They lined up to send a final golden cascade onto the beach, then shouldered the coolers and. began picking their way through a jumble of stony debris. It was not an especially hazardous or even an arduous trek unless one were burdened with a beer cooler or awash with the beer itself, or both. Finally, sweaty and winded, they paused to rest on a shelf or rock that formed the rim of a muddy basin. The basin drained into the marsh through a gap directly opposite the men; they had arrived at the edge of life's domain. The shelf sat atop a layer of porous rock from which water seeped. A film of algae covered the damp rocks. Scum floated in shallow pools that had collected in the basin, and each pool bordered a dense, bristling mat of greenery barely an inch thick. A band of desiccated plant matter around the basin's sides showed where life had fatally overreached itself.

Berry suddenly cried out, "Hey!" and pointed at something on the ground before him. "Come look at this."