The earliest plows where forked sticks and timbers. In the middle east the early plows were called ard. The early plows simply loosened the soil. (19F) A type of ard is still used in some underdeveloped countries today.
The major advance before 1000 A.D. was the development of the heavy plough, which was more than the simple plows farmers used earlier. It had a coulter which cut a thin strip in the turf. The coulter was followed by a share which would slice into the soil and then the soil would ride up the mouldboard which would turn it over. Later wheels were attached to this type of plow and later still a seat was added. By turning over the soil weeds were limited and overall it helped the growing process.
Metal was added to parts of the plow which increased it's efficiency. One of the major problems was that the dirt would become stuck on the plow and had to be cleaned off by hand. A second problem was that this system did not work in the dense grasses of the western plains. (19F)
The problem of the plains was solved by a black smith from Vermont named John Deere. Deere moved to Grand Detour, Illinois in 1836. He invented a blade which was self polishing and combined the share and moldboard into a one piece plow. Deere moved his factory to Moline Illinois and began manufacturing in 1847. The blade was an amazing hit and began the John Deere company. (19F)
Early farming utilized oxen ("any kind of cattle used for draft, or pulling work, are called oxen" (18F, pg 8) in the fields. These animals appear to be first used around 3500 B.C. with primitive plows made of wood.(18F) In Europe the invention of the horse collar and shoe in the 9th century allowed the plow to be pulled by horse. Yet even into the 18th century oxen still outnumber the horses partly due to the expense of feeding the horse. (17F) Yet with the advent of the iron plows many farmers changed over to heavy horses which could pull the new type of implements at a faster pace than the oxen. (18F)