Scientists study cause and effect. If there was a world-wide flood over the earth, then it would have left striking marks upon the earth. By piecing together many different discoveries over time, scientists have been able to construct a possible scenario of Flood events. In the Beginning, by Walt Brown, chronicles many of these studies. Here are a few memorable highlights.
According to the Bible, the "fountains of the deep" broke up. Water spurt out of the ocean with such force that it escaped our atmosphere and kept going. That's where we get our comets, which have the same water type as our oceans. (No comets have ever been observed to come from outside our solar system - only from within.)
Much of that water rained back down, some as snow upon the north where the mammoths were snowed under, food still in their mouths and bellies, uneaten or undigested. No mammoth can live in snow - modern elephants must keep moving around to hunt for food in order to grow, so how much more an elephant-like mammoth? There is just not enough food in the frozen tundra to keep any mammoths alive, much less grow to such a great size. In the past, the far north was warm and food was plentiful for them.
Every major mountain range on earth contains fossilized sea life - far above sea level. The author has found fossils of sea life a few miles from Mount Ararat, more than a mile above sea level. Several states above the Grand Canyon were filled with water for some time after the Flood. A dam in the south finally broke, gushing gigantic torrents of water southward. That water plowed into ground still somewhat softened after the Flood, and easily carved its way south to form the Grand Canyon.
These findings and more are still accumulating as scientists pursue this fascinating subject of the Flood aftermath.