When vertebrates lived in the sea, even at about 60ppb, there is a constant and

reliable source of iodine. However when some of the vertebrates did leave the sea, obtaining enough iodine did prove to been a challenge to their descendants,

including mankind. Iodine is used in thyroid hormones, T4, thyroxine, and T3,

tri-iodothyronine, controlling all development, postnatal growth, and ongoing

daily body metabolism. In fact; without iodine, no vertebrate life.

Land plants do not need iodine, their taking it in from roots or leaves may be

incidental. Only a few land plants are reliable or even adequate iodine sources

unless consumed in large quantities which is the case by large herbivores.

Plants grown proximal to the marine environment and those deliberately

fertilized with seaweeds can accumulate enough iodine to provide adequate

dietary supplies for herbivores and humans. Potatoes, garlic and other root

crops are the best accumulators.