Jay looked at the seas and land that peeked out from beneath the clouds of P-L5. He was anxious to get home to Earth, but he couldn't help but wonder at this beautiful and mysterious planet. "P-L5," as it was termed, had been home to a small human colony and thriving tourist industry for over a century when the inhabitants had fled to neighboring systems almost 100 years ago. Now Jay and his colleagues would be deciding whether or not a new colony should be attempted there. They didn’t have long to decide either--with all the chaos on Earth, nothing was getting much funding these days. Luckily, K&P Securities had offered to sponsor the side trip and a crew had been thrown together. The captain had given them a tantalizing description of the planet they would be investigating:

"Many of you have heard of P-L5, some of you may even have had family that once lived there. Let it stand as a reminder in your future travels never to underestimate and ignore the environment around you. The earliest record of this planet is from the year 2400 when the Fifth Quadrant was discovered. The description is of a simple beautiful planet ideal for human habitation--moderate oxygen levels around 5%, clear blue seas, and land for building. The only native life was a harmless collection of chemoautotrophs, photoautotrophs, and passive filter feeders. With a few environmental adjustments, the planet was settled in 2460 and became a mecca for tourists and for industry, at one time supporting a water distillation plant, farms, factories, schools, libraries, and research facilities. Then for reasons still unclear, things began to change; the inhabitants fled to new planets, leaving their towns and belongings behind. These ghost towns now stand very much as they were left 100 years ago when people still lived there. This is a two-day stopover. Enjoy the beach, look around, but be careful--we still don't know exactly what happened down there. I will expect a full report in three days detailing environmental and biological conditions on the ground as well as a decision on re-colonization."

As soon as the little shuttle landed, Jay burst out ready to explore. The first thing that hit him was the fresh air. Mmmm, oxygen. The early colonists had probably prepared the planet by pumping oxygen into its atmosphere to raise the O₂ concentration to earth levels--standard procedure back then. He walked towards the cluster of hulking buildings; the iron railings had begun to show signs of rust. He swung open the unlocked doors and stepped into the municipal building. Hopefully he would find a clue to this mystery among the scattered government documents lying about. He picked up a binder marked "water supply": early water tests had shown high oxygen content, moderate calcium carbonate levels, and low sulfur, nitrogen, and phosphates. Cyanobacteria were also present. Interesting. A memo dated 2480 complained of flat soft-bodied organisms, some up to one meter long, getting jammed in the deep sea intake pipes. Flipping through the entries he came across later notices and complaints: one memo about 50 years later noted tourist complaints about water taste and cloudiness, which the plant manager blamed on phosphate, sulfur, calcium carbonate, and nitrogen runoff from "those damn farms" and years of deep sea dumping by one of the offshore factories. Later reports noted an increase in harder bodied organisms being caught in the sea intakes. Jay pocketed several of the sketches.

It was starting to get dark by then, so Jay decided to take a quick walk to the shore before boarding the shuttle for the night. Walking through the empty streets, he wondered what had happened. Obviously the environmental change had been rapid, and he had a hunch the alien organisms had probably changed quickly as well. Rapid evolution was not unknown. He remembered once having to move camp every night to avoid a river bed that changed course by morning, or his aunt’s flower beds on Pentarch that came up in different shapes and colors every year. It would not surprise him if the change here had been fast--probably catching the colonists unprepared.

His boots crunched along the shore as he scanned the beach. A thin film of dirt had covered the old water intakes in the distance, and the murky water hid its secrets from view. He noticed what appeared to be deep burrows, several inches long, as the waves receded. Interesting. He took out the sketches. The planet's jelly-like, flat-bodied early life could not have made these; they lacked the firmness, strength, and three-dimensional body shape to tunnel. Whatever was living in these burrows was closer to the strange hard- bodied creatures that came later. He bent down to examine the tide pools that foamed around his feet. Maybe the waves had washed something ashore. He scooped up a tiny shelled creature no bigger than his thumb--it looked as if it had been bitten in half, and so had many of the larger life forms he found along the beach. So much for the harmless autotrophs; predation had obviously begun. Drawing a quick sketch of what he had found he ran back to the shuttle, determined to fit together the pieces to this planetary puzzle.

"Hey, Jay," one of his friends called out. "Since when did you start taking evolutionary biology? Nice sketches, but the trilobite looks a little funny."

"You know what these things are?" Jay asked in surprise.

"Sure, look up Earth's Late Precambrian, aka "Vendian" or "Ediacaran" period, and the Cambrian period (543 to 510 million years ago) that came after it. You can use my computer."

"You know, I think I will."

HERE'S THE SITUATION:

You have two days before you and your colleagues must decide the fate of this planet and the hundreds of people who are waiting to re-colonize it. Before you come to any conclusions, however, you need to find out exactly what happened on this planet, why it happened, and what the future possibilities are. Start with sources on Earth's Late Precambrian, aka "Vendian" or "Ediacaran" period, and the Cambrian period (543 to 510 million years ago). By the time you return to class to solve this case, you will need to know:

1. What was the Late Pre-Cambrian environment like on Earth?
   
2. What were the Ediacaran organisms like and how were they adapted to their environment?
   
3. How is Earth's Pre-Cambrian similar to P-L5's initial environment and organisms?
   
4. What was the "Cambrian Explosion"?
   
5. How did the environment and organisms change and adapt during the "Cambrian Explosion"?
   
6. What causes lead into the "Cambrian Explosion"?
   
7. Could any of those Earth conditions have been mimicked on P-L5? How?
   
8. Assuming that this alien planet was going through an Alien "Cambrian Explosion" that mimicked Earth, what do you think will happen next?

The Paper Trail:

• Memo dated 2480
  
• Memo dated 2530
• Drawings dated 2660

Internet Sites:

The Divisions of Precambrian Time
http://www.ucmp.berkeley.edu/precambrian/precambrian.html

Life of the Vendian
http://www.ucmp.berkeley.edu/vendian/vendianlife.html

Learning About the Vendian Animals
http://www.ucmp.berkeley.edu/vendian/critters.html

Oxygen Pulse and the Evolutionary Expansion of the Metazoans
http://www.geocities.com/CapeCanaveral/Hangar/8200/Oxygenation.html