PX282 - M1 - requirements for life
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the definitions of life are notoriously difficult and controversial, but its requirements are better understood through the study of extremophiles, mainly bacteria
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eg:
- temperature
C (hydrothermal vents at mid-ocean ridges) - ionizing radiation upto
lethal dose for humans - chemical extremes, like pH
- pressure
bar
- temperature
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the fundamental requirements are:
- energy source, eg: photosynthesis, chemosynthesis
- carbon source, as its valency allows complex organic chemistry. this is also unlikely to be a limiting factor due to its abundancy
- liquid water, which is a solvent by all all life on earth and is relatively rare in the solar system
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carbon-based life may not be the sole possibility, but H, O and C are the first, the third and the sixth most common elements
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liquid water needs moderate temperatures and pressure
bar -
the high temperature limit is set by organic chemistry
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hydrothermal vents are favourable for life because nutrients are abundant from heated water/rocks
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fossil evidence of life on earth
Gyr ago -
from the faint young sun paradox, it implies that liquid water must have been present
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this could be possible due to stronger greenhouse effect from higher atmospheric CO
abundance