Actually, those animals were destroyed before God made the present world arrangement. And while we've been focusing on mammoths & elephants, there's no accounting for the MILLIONS of species that are extinct that man apparently never saw. To have taken a pair of EVERY ONE of them aboard the ark woulda required an ark the size of a city.
As for the Grand canyon's sedimentary layer, there's evidence (not opinion or guesswork) that the area was covered by aeas at least 3 times, with Noah's flood being the topmost one. it's the only one where remains of modern life have been found.
And yes, people useta believe the earth was young til they found evidence showing otherwise. They also useta bellieve t5he earth was flat, & that the celestial objects revolved around us. Funny what a little FACT-FINDING can do!
And I believe that you believe God has always existed, as I do. It'd really be a stretch to believe He sat around twiddling His thumbs for a googolplex of a googolplex of our years til one day He decided to create a physical universe.
While you're to be congratulated & praised for trying to defend your beliefs, there's simply too much EVIDENCE against a young earth, (as opposed to imagination, opinion, & guesswork) such as the slow mountain erosion, objects in the sky being so far away it takes their light millions of years to reach us, and the FACT that over 99% of all species of life that's ever lived on earth is extinct, and was so before man coulda seen it. Nice try, but no cigar!
You would have a difficult time presenting any history that Christians believed that the earth was flat, or anyone else for that matter.
Also, you lack Scripture to prove you point. Science and Scripture align. Genesis is history. Our Lord Jesus Christ said that Adam and Eve were present at the beginning of creation, just as Genesis teaches:
Mark 10:6 (KJV) But from the beginning of the creation God made them male and female.
You have not accounted for the Great Unconformity that is found worldwide. And why would God destroy the world multiple times with floods when He promised after the first Flood that He would never again use water, but it will be fire next time.