The year is 2750. You are aboard a Starfleet shuttle approaching an Earth-like planet. Although anxious to get home to Earth, you can't help but wonder at this beautiful and mysterious planet with Earth-like seas and land peeking out from beneath the clouds. "L-305," as it was named, had been home to a small human colony and thriving tourist industry for over a century before the inhabitants fled to neighboring systems almost 100 years ago. Now you and your colleagues will be deciding whether or not a new colony should be attempted there. You don’t have long to decide either--with all the chaos on Earth nothing is getting much funding these days. Luckily, K&P Securities has offered to sponsor this side trip, and you and the other crew have been thrown together. The captain has given you a tantalizing description of the planet you will be investigating:

"Many of you have heard of L-305, 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 next week detailing environmental and biological conditions on the ground as well as a decision on re-colonization."

As soon as the little shuttle lands, you burst out ready to explore the surface. The first thing you notice is 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. You walk towards the cluster of hulking buildings and notice that the the iron railings have begun to show signs of rust. You swing open the unlocked doors and step into the municipal building hoping to find a clue to the mystery of this planet among the scattered government documents lying about. You pick 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 you come 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. You pocket several of the sketches.

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

Your boots crunch along the shore as you scan the beach. A thin film of dirt has covered the old water intakes in the distance, and the murky water hides its secrets from view. You notice what appears to be deep burrows, several inches long, as the waves recede. Interesting. You take 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. You bend down to examine the tide pools that foam around your feet. Maybe the waves have washed something ashore. You scoop up a tiny shelled creature no bigger than your thumb--it looks as if it had been bitten in half, and so had many of the larger life forms you find along the beach. So much for the harmless autotrophs; predation has obviously begun. Drawing a quick sketch of what you have observed, you run back to the shuttle, determined to fit together the pieces to this planetary puzzle.

"Hey!" one of your friends calls out. "Since when did you start taking paleontology? Nice sketches, but the trilobite looks a little funny."

"You know what these things are?" you ask 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."

"Thanks, I think I will."

HERE’S THE SITUATION:

You have one week 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 were environmental conditions like on Earth during the Late Precambrian?
   
2. What were the Ediacaran organisms and how were they adapted to their environment?
   
3. How was Earth during the Precambrian similar to L-305's initial environment and organisms?
   
4. What was the "Cambrian Explosion", what was the environmental context of this major evolutionary event, and what caused it?
   
5. How did the environment change during the "Cambrian Explosion"and how did organisms adapt to those changes?
   
6. Could any of those Earth conditions have occurred on L-305? How?
   
7. Assuming that this alien planet has experienced an Alien "Cambrian Explosion" that mimicks the history of life on 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

Cambrian Explosion Website
http://users.aol.com/kbclark/cambrian