So long ago, I asked on how to make Earth's oceans as brackish as Lyr's, one of the many worlds imagined by artist Chris Wayans. The only real answer I got was something that that world had already gotten covered--less land.

Simply speaking, the less land there is on the surface, the less rock there is to erode, and the less rock there is to erode, the less ions there are to be dumped into the oceans. That is how our oceans ended up being so salty.

So here is my map of an alternate Earth consisting of nothing but islands.

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If any specifics help with the scaling, it is equal in mass, diameter and gravity to Venus. It has no axial tilt, which means no seasons. The highest point above sea level is barely twelve feet. Mathematically speaking, is the proportion between land and water presented in this map enough to make the oceans freshwater instead of salty?

  • $\begingroup$ How about volcanism, you don't have any big volcanoes? $\endgroup$
    – Alexander
    Commented Apr 21, 2020 at 20:26
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    $\begingroup$ When you're talking geological timescales, I think that you cannot really keep only those few islands unless you have no plate tectonics. And without tectonic activity, I don't see how life could have evolved. These are just my ruminations though; I know nothing about this subject. $\endgroup$
    – KeizerHarm
    Commented Apr 21, 2020 at 20:28
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    $\begingroup$ @KeizerHarm That wasn't what I was asking. $\endgroup$ Commented Apr 21, 2020 at 23:35
  • $\begingroup$ Does the sea floor contribute nothing to salinity? $\endgroup$
    – rek
    Commented Apr 22, 2020 at 0:51

2 Answers 2


Probably salt water.

Over the past Billion years the salinity of the oceans has remained relatively constant. Part of the reason for that is that there are a lot of geologic forces that allow for the sequestration of salts. On a geologic timescale one of the largest sources of this is when inland seas get cut off and evaporate. When this happens large quantities of the global oceanic salt content gets removed. On your planet it's unlikely for such an event to happen given the lack of landmasses for salt deposits to form on.

  • $\begingroup$ salt water but it may have a lower concentration than on earth due to far less source material. If there is less volcanism there will be noticeably less salt. $\endgroup$
    – John
    Commented Apr 22, 2020 at 2:57
  • $\begingroup$ @John You can definitely handwave it either way if you want. If you want a way to have giant freshwater seas, just say "In this world the seas are composed of freshwater". Unless whatever you're doing with the world hinges on a detailed and accurate geological simulation, you'll only bore your audience by attempting to justify why with anything more than few sentences of fluff. $\endgroup$
    – sphennings
    Commented Apr 22, 2020 at 13:00

There are a few solutions.

The first depends on how old your planet is and how newly formed the oceans are. Newly formed oceans won't have had enough time to accumulate massive amounts of salt and will take millions of years to do so.

The second would be to inhibit the processes which add salt to the oceans, if there is no volcanic and tectonic activity there is less ways for deeply stored minerals to get mixed into the water.

Lastly the composition of your planet can be modified to have low amounts of sodium and chlorine, thus preventing concentrations of them to be dissolved in the oceans.


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