As the price and demand for oil and gas goes up worldwide, it becomes more lucrative to go after deposits of natural gas by more exotic methods. One of the most controversial methods is hydraulic fracturing, more commonly known as fracking. In this process, millions of gallons of pressurized water, chemicals and sand are injected deep underground to shatter permeable rock layers, making formerly inaccessible deposits flow to the surface. More than 20,000 natural gas wells have been fractured in the last decade in the U.S., and in these lean financial times, many property owners and communities have gladly sold or leased their land in support of this process. Still, many people fear the damage to the environment and especially the water table that might result. Here are the chief concerns about fracking, and a look at why the science in some cases is less settled than either fracking supporters or opponents would like to believe.