Biological cell/Talk

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Archaea are the oldest organisms existing.

What does it mean ? What evidence is available than they are older than bacteria ? (not to mention that this word has much meaning in evolutionary biology than people use to assume based on their false vision of evolution) --Taw

According to common theory, they are the ancestors of eukaryotes. By absorbing certain prokaryotes, they added new functions to themselves, becoming more complex in the process (endosymbiotic theory). Mitochondria and chloroplasts in eukaryotes, for example, are basically adapted bacteria.

They aren't any adapted bacteria. They were initially. Nowadays 95% of their structure is coded by cell nucleus, and they lost many other functions. --Taw

Today, several Archaea can only survive by adopting to extreme environments, e.g. geysers or black smokers. They can survive extreme pressure and heat, and can feed on methane or sulfur.

That's not that way. Some of them live in such environments, but many others don't. And this sentence is sugesting that such an environment is in some way inferior to Eucaryotic environment. It would be as silly to say that fish can only survive by adopting to extreme (underwater) environment. --Taw

And it's also misleading in that some researchers theorize that those particular "extreme conditions" (hydrothermal vents) may be where life arose in the first place. In which case, non-Archaea life could only survive by adopting to extreme environments, eg. dry land and open ocean.