The first Agricultural Revolution occurred around 10,000 and 2,000 BC. It was mainly the domestication of plants and animals. This was the transformation of human societies from hunting and gathering which is the oldest method for obtaining food, to farming, the first crop the people grew was wheat. It is practiced by small numbers such as the San of Southern Africa and the Aboringinals of Austrailia.
The second agricultural revolution originated in Western Europe around 1700's to the 1800's. The popular farming systems used were the plow, horse collar, and the seed drill which is far more industrialized compared to hunting and gathering. The used technology to increase production and to increase efficiency.
The third agricultural revolution occurred around the start of the 20th century to today. Farming has changed a lot because of technologic and scientific innovations. Mechanization, chemical applications, and biotechnology have changed the way we farm drastically. Today we use tractors and more engine based farming utilities, which has reduced the number of laborers and increased land.
GMO stands for Genetically Modified Organism. GMO's are plants and animals changed as a result of biotechnology. Pros of GMO's are they are more resistant to weeds, pests, and disease. And sometimes higher nutritional value. Cons to GMO's are mixing genes with different organisms and, some GM foods are marked without labeling. GMO's change farming because it changes the way farmers conduct their operations and biotechnology companies have been able to obtain patents with which to restrict their use. As a result, the companies that make GMOs now have the power to sue farmers whose fields are contaminated with GMOs, even when it is the result of inevitable drift from neighboring fields.