. >> reporter: jonathan foley of the california academy of science. >> well cows and goats and sheep in the brown areas. >> reporter: foley has actually mapped the land use problem. >> this is showing the footprint of agriculture on the planet. what really surprises people sometimes is that 38% of all the land on earth is covered in food. for example all of this land 75% of it a lot of those red areas and a lot of those green areas are used to produce meat. either directly by grazing or growing crops that we then directly feed to animals later in a feed lot. >> reporter: in addition, says jonathan foley, of the growing beef consumption in the less-developed world leads to deforestation, clearing the land for cattle. so, what says the defense? >> come cattle !! >> reporter: ha ha, look at this guy! will they respond to me or no, they don't know my voice. >> i doubt it's so much the voice as anybody who comes out here in an outfit like that. (laughter) >> reporter: in marin county, california, grass-fed guru bill niman and wife nicolette, defender of beef. >> what's so miraculous about