Many environments are considered "extreme" (boiling hot springs, acidic/basic water, etc) and those tend to be dominated by Archaea instead of the "usual" mixture of bacteria along with complex plants and animals. But "extreme" is in-part in the eye of the beholder.

Very little of earth (in terms of total energy available) is at 100C or pH 0, etc. Broadly speaking, the more organisms in parallel trying out various mutations the higher the chance there is to come up with something useful. We can't expect a 1km^2 hot-spring cluster or the energy-starved layer of groundwater at the 100C geotherm (about 3km below ground) to evolve as much as a 1000000km^2 rainforest exposed to direct sunlight.

There are large extreme environments. There is plenty of energy available in deserts such as the Sahara or the open surface ocean (an iron desert) but the primary productivity is very low. This means that the environment is harsh enough to stop life from adapting "effectively". Here "effectively" means how much of the available energy is used, i.e. what fraction of the sunlight is absorbed by the plant/algae (the conversion efficiency into glucose is very low, at most 7% and often ~1%, but we are ignoring that). Note that in many cases a desert is actually more hostile to microbial life because larger organisms can store water/nutriants/etc more easily.

On the other hand, there is one example of an "extreme" environment that became widespread and in which life thrived: Oxygen. O2 forms reactive species in a wide variety of biochemistry, which makes it a pretty universal poison. But life found a way around with enzymes such as superoxide-dismutase and was able harness the high energy or these reactions.

To the best of our understanding, to what extent would life have evolved and thrived if the entire Earth's ocean were an extreme environment, such as 100C, pH 0, or 34% salinity?


closed as primarily opinion-based by David, canadianer, kmm, another 'Homo sapien', AliceD Jul 5 '17 at 21:45

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ We cannot have any "understanding" of the outcome of a hypothetical postulate. Whereas discussion of this may be of interest to you and possibly others, there can only be subjective opinions on the question and therefore I am afraid that it is off-topic for SE Biology. (see: biology.stackexchange.com/help/dont-ask) $\endgroup$ – David Jul 3 '17 at 10:52