Short answers, pulled from the story.
Sheep and goats were domesticated by nomads before the first permanent settlements were constructed around 7000 BC. Cattle and pigs followed somewhat later, once people started to live in fixed settlements.
The Taylor Grazing Act of 1934 was enacted after the Great Depression to regulate the use of public land for grazing purposes. This act regulated public land use after the Great Depression following earlier practices where livestock were grazed on public land from the Civil War era.
A 2013 FAO report estimated livestock were responsible for 14.5% of anthropogenic greenhouse gas emissions. In New Zealand, methane and nitrous oxide from agriculture made up somewhat less than half of the country's greenhouse gas emissions in 2004.
More than 100,000 sheep graze at solar arrays primarily in the South United States. Organizations such as the American Solar Grazing Association promote best practices for co-locating solar energy and grazing operations.
Livestock grazing has severely degraded riparian areas in arid climates like Arizona and New Mexico. Over 90% of the original riparian zones of these states are gone according to the Arizona state park department.