Short answers, pulled from the story.
Salt preserves meat by using osmosis to draw moisture out of the meat and into the surrounding salt. When salt concentration reaches nearly 20 percent, it creates a solute-rich environment that is inhospitable to microbes.
The World Health Organization classified processed meats as Group 1 carcinogens in 2015 after reviewing over 400 studies. Each daily serving of processed meat raises lifetime bowel cancer risk by 18 percent according to their data.
Diodore of Sicily recorded that Cosséens people in Persia salted carnivorous animal flesh four centuries before Alexander the Great's campaign. Polybius described how Gauls exported salt pork to Rome every year during his time between 200 and 118 BCE.
Nicolas Appert developed air-tight storage methods in 1795 through experimentation that would become universal. The summer of 1857 in France was so hot that most butchers refused to slaughter animals due to inadequate conservation methods.
This method allowed the meat to remain preserved from 12 to 16 weeks, sufficient duration to reach Europe by boat. Chilled meats enabled New Zealand to compete more strongly with local producers of fresh meat globally.