Actually, let's think it through.And what is the best environment for marine fish ? water or land
Why to adapt to land while living in water ?
IF life started in water (which seems at least plausible since we are made of so much water).
THEN it seems reasonable that there were both plants and animals in the water.
Plants 'eat' sunlight and animals eat plants (some animals may or may not eat other animals at this point, so let's leave them alone for now).
As a sun eating plant, the empty LAND offers some advantages (more sunlight food is available above the water than in it and more nutrients are available in soil than floating free in the water).
So some random aquatic plant named Bob, has adapted to living right at the edge of mean high water. Bob lives almost exactly half of his life in the water and half of his life in the wet mud at the shore. The wet mud is crowded with plants fighting for every inch of space. Just beyond Bob's reach is the land that almost never floods where no plants live. One day Bob Jr spreads his seed and takes a shot at the open space beyond mean high tide. Bob Jr is a little thirsty, but it turns out that he can survive. Fast forward some long time and the decedents of Bob Jr cover vast swathes of the land that was free for the taking with very little competition and lots of delicious sunlight.
Fast forward some time and along comes Charlie the Fish.
By now, there are lots of fish that eat other fish, so the shallow water offers more food and fewer predators.
Unfortunately, a lot of other fish had the same idea, so the shallow water is crowded and competition for food is tough ... and just beyond reach are all of those plants that live on the land.
Now everyone laughed at Charlie because he still had that old lung to help him grab some air when all of the hottest and newest fish in the deep had upgraded to gills and a buoyancy bladder. That's what forced Charlie out of the deep water and close to the shore in the first place ... he was being out-competed in the deep water by more specialized designs.
But all of the other fish were laughing out the other side of their gills when the saw that Charlie could get right up to the water's edge and eat the plants that other fish could not reach.
Some of Charlies kids could reach even further onto the land than Charlie, and natural selection granted more food, fewer predators and more offspring to the decedents of Charlie who were better on land than water. Eventually, his decedents were born in the water and were able to live completely on the land.
The question is not How, but Why.
Was it all random chance? Bob Jr and Charlie Jr were just really lucky.
Did a Creator step in for a 'day' and say 'Let Bob Jr cover the land with plants, and it was so'?
Did a Creator step in for another 'day' and say 'Let Charlie Jr cover the land with animals, and it was so'?
Biology cannot answer Why, that is not Biology's job.
Theology can answer Why, but tends to be a little fuzzy on How.
I have questions about some of the details of How, but the process seems far too similar to what can still be observed in any disturbed field that transitions from the first small tough weeds and grases to a dense forest over several decades. I have seen how life works. How it struggles to fill every disturbed patch of dirt.
I have seen trees that self-hybridize without any human effort (the bane of my plant identification existence).
It is not an unreasonable leap to imagine that more time could yield more dramatic results.
In my opinion, adaptation does not prove that there is no God.
My faith is not built upon a flat earth, or the sun orbiting the earth, or the necessity of a 6000 year old universe.
If God exists NOW (and I find compelling evidence that He does), then God existed THEN, and the 'How' of creation is only an interesting footnote compared to the 'Who' of the story of Creation.
[I will have undoubtedly gotten some of the details wrong ... so what ... the underlying point still stands. How does not negate Who and Why.]