Salt seems trivial today, yet only a small fraction of the roughly 300 million tons produced each year is eaten. This episode explains why early hunter-gatherers got enough sodium from meat, and how the shift to agriculture created a biological deficit that drew the first settlements to salt deposits, from Solnitsata in Bulgaria to Xiechi Lake in China.

We follow salt as currency and trade good, bust the myth that Roman soldiers were paid in salt, and look at preservation, salting the earth, and the taxes that fueled revolt, from the French gabelle to Gandhi’s salt march. Then we turn to salt’s hidden industrial life, giant mines beneath Lake Huron and in Pakistan, how sodium works in the body, the U-shaped risk curve, and fortification with iodine, fluoride, iron, and folic acid.

• Why the agricultural revolution made salt a necessity and how the Tuareg Azalai caravans still carry it across the Sahara
• The real etymology behind salary and salad, and why historians doubt the salting of Carthage
• How the chloralkali process turns salt into chlorine for PVC, paper, rubber, and drilling fluids
• Inside the Sifto mine under Lake Huron and the room and pillar Khewra mine with its salt mosque
• How sodium drives nerve signals and blood pressure, and why both very high and very low intake carry risk