What caused the Cambrian explosion of life?

[Archbob]

This is not a creation vs. evolution debate. The question here is what caused the Cambrian explosion of life, not, did it happen. For the purposes of this discussion we're going to assume evolution is true. If you do not believe in evolution, then do not partake in this discussion.

So around 500-600 million years ago, life on earth suddenly exploded from single-celled amoebas to jellys, shrimps, etc.

We know this explosion happened with the span of 10-20 million years. However, we know that life began on earth over 1.5 billion years before this point. So why did life suddenly explode during this time period when it had not in the 1.5 billion years previous?

 

[sanabas]

Probably multiple reasons, but off the top of my head I think one of the main ones was the appearance of the first triploblasts.

 

[Adebisi]

I haven't looked into it so much, but I find the snowball earth theory very likely. The composition of the atmosphere changed to contain much more oxygen.

 

[Oerdin]

Basically the amount of oxigen in the atmosphere was the limiting factor and we know from the banded iron formations found in nearly all early pre-cambrian rocks but not found in cambrian or younger rocks that suddenly there was more oxigen. We stopped seeing banded iron formations because the level of oxigen as a percentage of atmosphere got so high the iron started oxidizing (rusting) instead of simply being laid down as neat semdiment bands.

 

[bathsheba666]

I heard that the pre-Cambrians experienced a sudden shortage of condoms.

 

[Archbob]

I do know the snowball earth theory around the pre-cambrian/cambrian break and that the amount of Carbon Dioxide decreased dramatically during that time. But is there a reason more advanced species couldn't have evolved that used Carbon dioxide?

 

[YNCS]

Plants use carbon dioxide and emit oxygen as a waste product. Before the Cambrian animal explosion, there was a rapid increase in plant life.

 

[Archbob]

Plants use carbon dioxide and emit oxygen as a waste product. Before the Cambrian animal explosion, there was a rapid increase in plant life.

There was no such increase for 2 billion years, then in the span of 10 million or so years all the animal and plant life appeared. It must have to do with changing atmosphereic conditions.

 

[YNCS]

My comment had to do with the increase of atmospheric oxygen.

 

[Oerdin]

The plants are what was changing the atmosphere. It must have been scary since almost all life at the time had evolved to not need oxigen or to survive on the very low levels of oxigen then in the atmosphere. The plants were pumping out huge amounts of oxigen which was a poison to most animal life at the time.

Suddenly you had a complete change in living conditions with oxigen levels going up to the low teens (low by today's standards but very high by previous standards) and with the evolutionary field wide open. The increased oxigen allowed everything to get bigger then the tiny animal forms which had previously existed and it was virgin territory (evolutionarially speaking) so life evolved quickly. Thus the Cambrian explosion.

 

[EdwardTking]

The ultra-violet revolution killed off land and floating plants so oxygen levels were minimal. Now one of two things happened: either a plant evolved the ability to withstand ultra-violet radiation and/or the small trickle of oygen created over two million years reached a critical level at which a protective ozne layer formed. Water surface and land plants took off leading to more oxygen and a thicker ozone layer.

 

[ybbor]

The plants are what was changing the atmosphere. It must have been scary since almost all life at the time had evolved to not need oxigen or to survive on the very low levels of oxigen then in the atmosphere. The plants were pumping out huge amounts of oxigen which was a poison to most animal life at the time.

Suddenly you had a complete change in living conditions with oxigen levels going up to the low teens (low by today's standards but very high by previous standards) and with the evolutionary field wide open. The increased oxigen allowed everything to get bigger then the tiny animal forms which had previously existed and it was virgin territory (evolutionarially speaking) so life evolved quickly. Thus the Cambrian explosion.

wait, so because oxygen was poison, and most animals weren't adapted to it at the time, they got bigger and more complex?

 

[Bill3000]

wait, so because oxygen was poison, and most animals weren't adapted to it at the time, they got bigger and more complex?

The change in living conditions include the adaptation of oxygen as part of metabolism, rather than a previous poison.

 

[ybbor]

but wouldn't a change to existing systems mean a regression to a more simple form of life? you can't expect a more complex change to arise when you force the population to change to a different resource

 

[blackheart]

There wasn't a really an "explosion." A Short History of Nearly Everything by Bill Bryson has a fair description. Basically, all those different organisms had existed before the Cambrian explosion but they weren't big enough (or something along those lines) to really be fossilized and discovered, so people think that they just suddenly showed up.

 

[Aramazd]

but wouldn't a change to existing systems mean a regression to a more simple form of life? you can't expect a more complex change to arise when you force the population to change to a different resource

When oxygen is used in respiration it produces much more energy than respiration without oxygen, which, IIRC, allowed animals to get larger.

 

[Cuivienen]

There was no such increase for 2 billion years, then in the span of 10 million or so years all the animal and plant life appeared. It must have to do with changing atmosphereic conditions.

Perhaps. Another theory is that the slow build-up of diversity suddenly led to a sort of "critical mass" of diversity beyond which natural selection went wild in causing speciation.

 

[The Last Conformist]

Probably multiple reasons, but off the top of my head I think one of the main ones was the appearance of the first triploblasts.

The oldest known triploblasts are considerably older than the Cambrian explosion.

One of the really notable things about the explosion is that alot of disparate groups take up hard calcified bodyparts at the same time. This suggests that changing oceanic chemistry played an important rôle.

 

[Abaddon]

lots and lots of mutations which allowed more and more niches to be occupied

 

[ybbor]

There wasn't a really an "explosion." A Short History of Nearly Everything by Bill Bryson has a fair description. Basically, all those different organisms had existed before the Cambrian explosion but they weren't big enough (or something along those lines) to really be fossilized and discovered, so people think that they just suddenly showed up.

so do we have evidence of these previous forms?