known to be major contributors to climate change. but now some scientists are arguing that cows can actually be a part of the solution. here is cnn s bill weir to explain. reporter: in the beginning was the buffalo. tens of millions of them wandering the land munching wild grasses and using poop and hooves to create rich, fertile soil up to 15 feet deep. look at this. but since americans replaced buffalo with cows, generations of fertilizers and pesticides tilling and overgrazing have turned much of that nutrient-rich soil into lifeless dirt. but not on farms where they graze cows just like wild buffalo. so adaptive grazing is a way that mimics the way bison moved across the great plains. so it s really about the animals hit an area really hard and then they leave it for a long time. reporter: peter bick is a professor at arizona state