Short answers, pulled from the story.
A plough is a farm tool for loosening or turning soil before sowing seed or planting. Its prime purpose is to turn over the uppermost soil, bringing fresh nutrients to the surface while burying weeds and crop remains to decay. Ploughing and cultivating soil evens the content of the upper 12 to 25 cm layer, where most plant feeder roots grow.
The heavy iron mould-board plough was invented in China's Han Empire in the 1st and 2nd century AD. From China it spread to the Netherlands, which led the Agricultural Revolution. Pre-eighteenth-century European mould-boards were usually wooden and straight; the curved mould-board design that transformed European farming arrived in the 18th century.
The modern word plough comes from the Old Norse plógr and is therefore Germanic, but it is thought to be a loan from one of the north Italic languages. The Raetic word plaumorati, recorded by Pliny, meant wheeled heavy plough. The word must have originally referred to the wheeled heavy plough, which was common in Roman north-western Europe by the 5th century AD.
The stump-jump plough was invented in 1876 by Australian Richard Bowyer Smith alongside his brother Clarence Herbert Smith. It was designed to break up new farming land containing tree stumps and rocks that were too expensive to remove. A moveable weight holds the ploughshare in position and allows it to jump clear when it strikes an obstruction.
In 1837 John Deere introduced a polished cast-steel plough that was so much stronger than iron designs that it could work soils in US areas previously thought unsuitable for farming. Deere, working as a blacksmith in Illinois, had noticed that a polished surface reduced the effort needed to move through resistant material and experimented with portions of saw blades before settling on polished cast steel.
In northern Europe, the mouldboard plough typically required four to eight oxen to pull, which was more than a single peasant household could muster, so its use demanded cooperation between multiple households. Historian William H. McNeill argued that this enforced cooperation with non-family members was conducive to the prevalence of the corporation in medieval Europe. The plough also contributed to the rise of the manorial system and led to farming being seen as men's work because of the implement's weight.