The Earth absolutely changed after Noah's flood, you can see lifespans decrease rapidly after that.
Code:
Before the Flood
Biblical Patriarch Life Span Age at Birth of First Son
Adam 930 130
Seth 912 105
Enosh 905 90
Cainan 910 70
Mahalealel 895 65
Jared 962 162
Enoch 365 65
Methuselah 969 187
Lamech 777 182
Noah 950 500
After the Flood
Biblical Patriarch Life Span Age at Birth of First Son
Shem 600 100
Arphaxad 498 35
Salah 433 30
Eber 464 34
Peleg 239 30
Reu 239 32
Serug 230 30
Nahor 148 29
Terah 205 70
So the environment changed drastically, and lifespan decreased rapidly after the flood.
And animal size probably decreased as well. Reptiles will generally keep growing as long as they live, so perhaps the early dinosaurs lived very long lifespans and this accounts for their giant size.
I do believe there were dinos after the flood as evidenced by the countless legends of dragons from many civilizations over the centuries. Some ancient art shows dinos that were not quite as large as we know today, perhaps because their lifespans were also shortened after the flood.
But the flood is not the only major global cataclysm. The Bible says the Earth was divided in the days of Peleg.
Gen 10:25 And unto Eber were born two sons: the name of one was Peleg;
for in his days was the earth divided; and his brother's name was Joktan.
Some believe that the Earth was undergoing violent change for hundreds of years after the flood. When the continents divided in Peleg's time there would have been tremendous earthquakes, volcanoes, and perhaps an ice age. There are some references to this in the book of Job.
Job 9:5 Which removeth the mountains, and they know not: which overturneth them in his anger.
Job 9:6 Which shaketh the earth out of her place, and the pillars thereof tremble.
Job 28:9 He putteth forth his hand upon the rock; he overturneth the mountains by the roots.
Job 12:15 Behold, he withholdeth the waters, and they dry up: also he sendeth them out, and they overturn the earth.
Job 38:29 Out of whose womb came the ice? and the hoary frost of heaven, who hath gendered it?
Job 38:30 The waters are hid as with a stone, and the face of the deep is frozen.
These are just some of the many verses in Job that may indicate the world was undergoing violent changes in his day.
As far as Mt. Everest being covered by water, the Bible is clear that all the mountains were covered in Noah's flood. But that doesn't mean Mt. Everest was covered, it may not have existed until the Earth was divided in Peleg's day. The continents dividing and shifting caused huge mountain ranges to be pushed up.