The Cambrian Period – An Explosion of Life
540 to 490 Million Years Ago
The Cambrian was inhabited by wondrous life forms, many of which
would seem alien to our modern senses and it is the “Cambrian
Explosion” that sets this period apart. Early in this period a large
number of experimental, unprecedented life forms appeared, differing
greatly from one another. Remarkably these creatures did not differ
on the species level, as does a tiger from a whale, but their
differences were more profound. They differed on the same level
(phylum) as the tiger differs from the sand dollar. And it is even
more amazing when it's considered that not too long before this
there were only simple single-celled creatures
Since Cambrian times the variety and originality of Life has actually decreased,
leaving us with our eight phyla and a whole host of questions. Normally we
perceive the development of life as growing from the simple to the complex with
great diversification along the way. But in the case of the Cambrian, it is just
the opposite. Since the Cambrian, we have lost the great range in the diversity of
body plans.
As all good things must come to an end, so it was with the Cambrian.
This fantastic experiment was ended by the Cambrian Extinction at
the end of the period.
Oxygen, Carbon Dioxide and the Atmosphere
- Oxygen and carbon dioxide played important roles in the development of
various body plans. This is a recurring theme throughout Eons and Epochs,
and here the foundations will be laid, to be further expanded and built upon in subsequent
sections.
Geography – Continents and Oceans
- Due to the continental shifts and the rising oceans, most of the continents
were covered in a shallow sea allowing marine life excellent access to sunlight
which constitutes one of the significant factors for the Cambrian
Explosion.
- The Cambrian witnessed the most rapid movement of the
continents of any age.
Climate
- Although the climate was warm and humid, sand dunes were the norm for most
areas above sea level. The emergence of land plants would have to come
later.
- Due to the flat terrain and widespread seas, the winds were able to blow
strong
and steady making the land inhospitable.
Plant Life
- All plant life lived in the oceans and seas.
- There were no land plants to keep the soils in place thereby impacting both
climate and geography.
Animal Life
- Trilobites first appeared in the Cambrian.
- Large vertebrates with hard skeletons made of calcium carbonate first emerged, completely changing the entire dynamic of predator and prey; it was essentially an “arms” race between the two antagonists where each side tried to come up with the innovation that would provide the advantage.
- The first fish appears in the fossil record. These fish were
jawless (similar to the modern lamprey) and bear the name
Agnathids.
- The Cambrian Explosion occurred early in the Cambrian.
- What were the causes?
- In most places around the world the sediment layer between the Precambrian and
Cambrian is missing so it is difficult to witness any developments leading up to
this explosion of life.
- Many weird and wonderful creatures can be found in the famous Burgess Shale fossil beds in
Canada. This list includes the following:
- Hallucigenia
- Wiwaxia
- Anomalacaris - nearly 20 inches long - one of
the largest predators known until the late Cambrian
- Hallucigenia
- In most places around the world the sediment layer between the Precambrian and
Cambrian is missing so it is difficult to witness any developments leading up to
this explosion of life.
- What were the causes?
Extinction Events
- Two extinction events occured during the Cambrian
