Why did land animals evolve back to aquatic environments?

Life on Earth began in the water. So when the first animals moved onto land, they had to trade their fins for limbs, and their gills for lungs, the better to adapt to their new terrestrial environment. ... In air, eyes can see much farther than they can under water.Explanation:

Life on Earth began in the water. So when the first animals moved onto land, they had to trade their fins for limbs, and their gills for lungs, the better to adapt to their new terrestrial environment. ... In air, eyes can see much farther than they can under water. Tetrapods evolved from a group of organisms that, if they were alive today, we would call fish. They were aquatic and had scales and fleshy fins. ... Between 390 and 360 million years ago, the descendents of these organisms began to live in shallower waters, and eventually moved to land.

Explanation:

the correct answer is: d. the saltine and pretzel are made of flour, yeast, and baking soda, and salt. the pecan contains no flour but it does contain fats. the pecan is a nut that can be consumed as a healthy snack. first of all, pecans are a source of fat (monounsaturated fat), but they provide less fat than some other nuts. pecans are a rich source of dietary fiber, manganese magnesium, phosphorus, thiamin, vitamin e…

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.