Final answer:
The maximum concentration of NaCl for oceanic life varies as different species have adapted to different salinity levels, with microbes called halophiles able to tolerate nearly saturated salt conditions. The fact that marine life thrives in current ocean salinity may be somewhat fortuitous, but life's adaptability suggests it might still have evolved under different conditions.
Step-by-step explanation:
The maximum concentration of NaCl for life in the oceans to be possible is not a precise figure, as different organisms have varying levels of tolerance to salinity. However, most marine life is adapted to the current salinity of ocean water, which is about 3.5% or 35 grams per liter.
Microbes known as halophiles can thrive in much higher concentrations of sodium chloride, even in environments where the water is almost saturated with salt.
It is contingent on a delicate balance in the ecosystem which evolved over millions of years. Some researchers argue that early terrestrial life was adapted to high temperatures, which could suggest that life originated in hot environments, possibly even on different planets like Mars, before coming to Earth.
The fact that life exists at all in our oceans is somewhat due to the fortunate circumstance that the concentration of NaCl and other conditions were suitable for life to begin and evolve.
The question of whether the original concentration of NaCl in the oceans was fortuitous is complex. It implies that if the concentration had been higher, conditions might have been too inhospitable for life as we know it to evolve.
Still, life on Earth has shown remarkable adaptability; extremophiles can withstand harsh conditions, including those with high salinity levels, suggesting that life might still have found a way.