A world with Freshwater Oceans

I don't get it.

In chemistry CaCO₃ is not the same as CaCo₃.

Though I do wonder what super-low salinity would do to nerve signaling and other biochem stuff...

edited 28th May '15 12:23:09 AM by Luthen

Hmm. Interesting point. Low salinity implies a lack of useful alkali metals. There may be other ways to run a nervous system, but they might be less efficient.

OR an ecosystem which has a very high, much higher than Earth's rate of consumption of alkali materials and salts.

The sea doesn't get any saltier than it already is because geological, chemical and especially biological sources take out as much salts and stuff as comes in.

Hence me saying "useful" alkali metals (a planet with a lower amount of alkali metals period would probably not be very earthlike). If they're tied up in some form, they're not accessible.

You know, the whole A Wizard Did It angle could work if the entire point of the story was dealing with an extremely powerful wizard who was doing things like make a water planet where the largest bodies were fresh without caring about consequences or considering how it was supposed to work.

If the planet itself is to be the focus, it might not be the preferred way to go about it though.

Perhaps most of the planets salt could come from high salinity saltwater lakes.

There were some before it, they're just gone now. A big reason why Baikal (like Tanganyika) survives as long as it has is geology. It's a rift valley. The crust is pulling apart and getting thinner and the lake as a result gets deeper and deeper. The oldest lakes presently on Earth are all rift lakes.

I imagine semi-aquatic creatures and fully aquatic animals descended from terrestrial ones would be much more common as the lack of salt would make the transition from land to water a much quicker and easier process.

You need specific adaptations to spend significant amounts of time in saltwater, in freshwater you can swim as much as you want, also if you look at lakes and rivers you'll see that freshwater generally has a greater abundance of organic matter which feeds living things.

Yes, but on our world, the only fully aquatic animals descended from terrestrial animals are ocean-based

Once organisms have figured out how to live in freshwater, it's obviously more ideal for them, but the salinity of seawater was critical to the development of life from its earliest moments.

"Yes, but on our world, the only fully aquatic animals descended from terrestrial animals are ocean-based"

That's probably because there is a significantly greater diversity of ecological niches in the sea—itself a function of the fact that life first evolved there. It's easier for a new species to fit itself into a more complex environment.

When I think of a world with freshwater oceans, I usually imagine a terraformed planet that has been populated with earth based organisms.