Alien Evolution:

The Return of the Cambrian Explosion

Part II

You can hardly wait for dinner to end. Your mind is racing with a hundred theories and ideas. It had taken the colonists less then 100 years to dramatically change the planet. Could the colonists' planetary "adjustments" have adjusted more than they intended? How had it affected the native creatures? Could the murky water be hiding new animals? Predators perhaps? And why had the people fled? Once at the computer console, you log into an old History of Life book, and what you find is shocking:

"The Ediacaran Period (also referred to as the Vendian or Late Precambrian) occurred from approximately 700 million years ago until 543 million years ago Earth time. The period was noted for its simple soft-bodied Ediacaran fauna, mainly autotrophic chemo and photo autotrophs and symbionts as well as filter feeders and passive nutrient absorbers, all inhabiting the deep oceans (see "Ediacara" and "Burgess Shale"). Oxygen levels were still low (approx. 5%), although cyanobacteria (blue green "algae"=bacteria) were slowly raising the O2 concentration. Great environmental and biological changes began that would have far-reaching impact. Massive glaciers dumped tons of sediment rich in nitrogen, sulfides, calcium carbonate, and phosphates into the seas, encouraging new life forms that grazed on the bacteria-covered nutrients, and providing the calcium carbonate and phosphates that would later be used to make shells. The oceanic and atmospheric oxygen concentration reached a threshold, wiping out some life forms while allowing others to raise their metabolic rates and thrive (see "Oxygen Revolution"). The appearance of early predators towards the end of the Precambrian signaled the shift in feeding styles from autotrophs to heterotrophs, which is associated with the predator vs. prey "evolutionary arms race." This intensified struggle to survive encouraged faster mobility (possible because of O2 metabolism), shells and claws (i.e. increased mineral content of sea) and neural sophistication (nerve nets to ganglia and eventually a notochord). Together these environmental and biological factors led to the "Cambrian Explosion," a period of fantastic evolutionary change and diversity lasting for a few million years and beginning approximately 543 million years ago. In that short period, all but one of the major phyla and body patterns evolved." --On-line text: Evolutionary Biology: Earth and Beyond, 2660.

Now you are getting somewhere. You take the creased sketch paper from your pocket and compare the strange drawings to the text book illustrations. Sure enough, the paper matches almost exactly the ancient fossil illustrations from the screen. You look at the simple drawings in awe. How, you wonder, could creatures from the Earth’s distant past have surfaced on an alien planet millions of years in the future? Although the planet had originally seemed to fit Precambrian Earth’s calm description, there had been no major glacial events, no undersea volcanos or millennia of oxygen-building bacteria. Could the colonists have inadvertently tipped a planet on the edge of an alien "Cambrian Explosion?"

You are beginning to feel a bit uneasy as you consider the following: Let us assume that the early colonists found conditions here similar to Earth’s Precambrian, and that this simple planet was indeed slowly changing as Earth had been in the Precambrian. And let us say that the colonists speeded up the process exponentially by dumping in oxygen and sediments. Also assume that the environment and organisms were able to evolve at an incredible speed (" break neck evolution" was a recognized phenomenon on some alien planets). If the path of evolution on L-305 had followed that on Earth, seas would have turned murky with sediment, "Ediacaran fauna" would have given way to a host of shelled, swimming, and burrowing creatures clogging the water pipes. Predators like Earth's meter-long Anomalocaris would have scared tourists and residents alike. Perhaps a frightened populace decided to get out before it was too late, before the new creatures emerged from the sea to take their first steps on land as Earth's creatures had later done. By next week you and your colleagues will have to make a decision that will affect hundreds of people and an entire planet: whether to re-colonize L-305 or leave it for good. What you need is information--enough to convince an entire team of scientists, investors, judges, and colonists of just what they what re-colonization would involve.

HERE’S THE SITUATION:

Next week you will be expected to present a full report on the environmental and biological conditions on L-305 as well as a decision on re-colonization. Each member of your group will represent one interest in this decision such as scientist, colonist, investor, etc., and will have to support your group’s decision before a preliminary court. Be prepared to justify your decision with theories on evolution as well as actual examples from Earth. In addition to other materials, you will need to know:

Discussion Questions about Earth:

  1. How were the Ediacaran organisms on Earth adapted to their environment?
  2. What major changes were occurring in the environment around the time of the "Cambrian Explosion"? E.g., what led to Earth’s "Cambrian Explosion"?
  3. Which of these changes were affected by the organisms themselves; which were purely geological trends?
  4. What came after the "Cambrian Explosion"?
  5. How long after the "Cambrian Explosion" before life emerged onto land, and what forms did this life take?

Discussion Questions about L-305:

  1. What were the initial conditions on L-305?
  2. How were those conditions similar to "Vendian" Earth? How were they different?
  3. How did the colonists change L-305? Why did they change it, and what effects did those changes have on the planet and native organisms?
  4. On L-305, if humans changed the environment in ways mimicking the forces on early Earth, do you really think that "Earth-like" animals would have evolved again? Why or Why not?
  5. Assuming that this planet was undergoing an "Alien Explosion" similar to the "Cambrian Explosion" on Earth, what would you expect to evolve next?
  6. Could the "Alien Explosion" on L-305 be slowed or controlled?
  7. Is the planet safe for colonization? Why or Why not?

Thank you and good luck! Hundreds of people are awaiting this mission's final decision.

Your Role Assignments: