[neilep (OP)]

Greetings !


I was wondering about the origins of life on Earth..(as you do)...

....The first land dwelling animal life I think is generally accepted as something that crawled out the sea yes ?..presumably that sea was salty ?...so...

......how did it manage to survive the transition from salt water to fresh water ?....how did it evolve to adjust to fresh water ?

...being an abundance of sea water....why not stick with it ?

..Is there life currently on the planet that can exist in both salt and fresh water with no probs at all ? (plant life included...but I'm really asking about animals and stuff)

[DoctorBeaver]

Well, there are eels and salmon for a start. As for animals, I'm sure some otters live in estuaries where there would be both fresh & salt water. I dare say there are others.

[Bored chemist]

"being an abundance of sea water....why not stick with it ?"
If all the other animals were in the sea and you could live in rivers you would have all that space to yourself with no competition. That's a major evolutionary advantage.

People are roughly as happy in sea water as fresh.

[Karen W.]

eels and salmon would have been my thought also, just as Doc said! We have actually had a baby otter up river via the mouth where it opened into the ocean... it was quite young and was in some kind of despair without its mother. people from the college had to return it but fortunately Mommy was found easily hollering for her pup near the mouth on a rock. Someone had spotted the pup earlier in the morning and they were reunited within a few hours . The suspicion was they had only been separated a very short time as m
Mommy was still quite vocal!

What a cool Question!

[chris]

What adaptations do these animals use that enables them to inhabit both salty and fresh water environments? There must be some switch in physiology to make this possible. Does anyone know what it is and how it is achieved?

Chris

[paul.fr]

..Is there life currently on the planet that can exist in both salt and fresh water with no probs at all ? (plant life included...but I'm really asking about animals and stuff)

Neil, there are two types in fish that can do this. Firstly the are Anadromous fish, these are fish that migrate between freshwater and saltwater. Secondly there are osmoregulators.

This site has some good information on osmoregulation: http://www.cartage.org.lb/en/themes/sciences/Zoology/AnimalPhysiology/Osmoregulation/Osmoregulation.htm

[dkv]

Evolution is a very slow process . However a transition from
Sea Water to Fresh Water is not necessary and possible if the habitat or the environment does not change or the if the changes occur suddenly.
So the gradual  changes (taking millions of years ) resulted into migration .... there was no one cause but many. The changes in cells took place very slowly and in different directions
... one cant even make fast forward film of the evolution .. it is so slow.