<< home  < Articles

On 30/8/2002, Bill (WM) posted:

What caused the Cambrian Explosion. Why do fundamentalist religionists seem to think it a flaw in the Evolution argument? Have there been other such explosions?
 

Zero replied

Large connected populations will give slow evolution with speciation being chronological rather than geographical.  [Peter, should that be geograpic or geographical?  chronologic or chronological?]

Scattered populations with very few exchanges would give rapid adaption (or extinction) with speciation occurring rapidly in
geographic arenae (Help! again please peter).  This would result in events like the Cambrian explosion.

It might seem a flaw in evolution because changes could be very rapid and from the fossil record appear as a spontaneous change.

I would think, but do not know, that there have been many and that they would accur regularly after each 'disaster' the Earth has encountered.  There should be some evidence of smaller but similar events after each ice age.
 

From my (possibly limited ) understanding of the topic, the Cambrian Explosion was mainly caused by a build-up of oxygen in the atmosphere of the Earth. The earliest life forms on Earth were fermenting anaerobic organisms, however when the photosynthetic cyanobacteria evolved, oxygen was released into the oceans and eventually into the atmosphere. (This process took a while as the first oxygen chemically bound to the dissolved iron in the oceans of that time, causing the iron to precipitate out, forming the banded Iron Formations seen today.) Once oxygen was available for use, the previous anaerobic organisms had three "choices" 1) Die because of this nasty toxic gas 2) move to an environment the oxygen could not reach (deep in muds etc, where we still find them) 3) evolve into forms that could tolerate the oxygen.

Those that took the third pathway had a decided advantage- the oxygen allowed the to gain their energy by respiration, rather than by fermentation. The extra energy then led to more complex biochemical processes than previously possible, and the formation of compounds such as collagen cartilage and chitin, as well as calcium carbonate. All these can be used as support mechanisms for cells, and multicellularity, again utilising the extra energy that oxygen afforded, "took off". The critical mass of oxygen in the atmosphere occurred just before the Cambrian, so that suddenly there were lots of things with hard parts able to be fossilised in the rocks. The geologists noticed this sudden appearance and termed it the Cambrian Explosion, ie life "exploding" onto the planet. Possibly life before the Cambrian Explosion was also nearly as diverse as just after, but the record is not as preserved due to the lack of fossilisable material.