In truth the cambrian explosion does represent a sudden explosion of fossils(relatively speaking) It appears that prior to this most life forms on the planet lacked any hard parts, which of course fossilize more easily.
The questions opened up by this are as follows.
Does this represent adaptive radiation?
If not what caused the sudden acceleration of evolution?
And if so what caused a probable homologous ecosystem to become compartmentalized. Like islands on an island chain?
Several
scientific theories are as follows.
Major predation begins here. Predation leads to local populations being forced to adapt. Predators once decimating local populations will moce. Both predator and prey adapt as a natural arms race takes place. Predators move from one type of prey to the next effecting every type of organism.
Major techtonic activity. Movement of continental masses changes the environment of long existing populations, causing isolation and forcing adaptation. Thus accelerating the forces of evolution.
Oxygen levels in the oceans finally have arisin to the level necessary for larger life forms. Anaerobic microbes die off as oxygen poisons the oceans. Microorganisms responsible for the formation of silicates and carbonates no longer need to compete with anaerobic microbes which once dominated the oceans.
The development of various hox genes, which help to organize a colony of cells. With the development of a central method of organization life was now free to try various forms. Eventually the selective pressures of predation and competition will lead to most of these forms to fail.
It could be a combination of these and other posibilities. We will never really know.
It is not length of life, but depth of life. -- Ralph Waldo Emerson