URA: There is not a trained geologist on earth who thinks there was a worlwide flood 4000-6000 years ago. There are many reasons for this. Here's one: (It's science, but it's not too hard, so please try to follow along.)
Sediments form on the bottoms of lakes, from the particles of earth that settle there. They form mud at the bottom. After millions of years of pressure, these harden into sedimentary rocks. In the summer, the layer is darker, from the organic matter in the soil. In the winter, it's lighter, as sand blows in. So you get 2 layers per year, that make a striped pattern. Much later, the lake is gone, and eventually you get striped layers of rocks where the lake was. If there is an upheaval, you can see the many layers of sedimentary rocks, with each dark/light stripe corresponding to a single year. They are called varves, and they look like this:
See the stripes? Each pair of stripes = 1 year.
So, if you have some poor graduate students to do it, it's possible to actually count the period that the lake was there pretty much undisturbed, continuously, with no major flood.
You guessed it. Those clever geologists have done this for many locations all over the world. And in many of them, there has not been a flood for thousands and sometimes millions of years.
In just one example, the Green River formation (not far from me) there are many outcrops like this:
Eventually, they have been able to piece together 6 million years without a major flood.
Another famous one is Lake Suigetsu in Japan, where they have very clear 50,000 layers.
So we know that there has been no flood in these particular locations during that time period. When there is a flood, we can clearly see the extra thick layer of sediment when it happened. In this way, we can look for and find evidence of ancient floods. And it's just one of the many ways there has not been a worldwide flood.