where did fresh water come from.

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There are dozens of theories attempting to explain the histrocial changes that may or may not have occured through the history of Earth (whatever length of time it may be).
The simple answer of freshwater's source is rainfall leading to run off, leading to rivers and lakes as we currently see them around us.

Studies reflecting reason for saltwater in oceans and various isolated lakes and the 'long term history of the water cycle' are highly conflicting - and none tend to agree with each other. But it's with good reason. We don't know enough about the climate of Earth prior to recorded history. That leaves the only logical conclusion to be that we don't REALLY know yet. There are too many conflicting 'facts' that cannot be proved. Most current studies set out with a stated goal to prove, and manipulate math and numbers fit the answer someone is trying to show they are right. Very few researches these days will look at the numbers and draw conclusions from them.
 
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