Gaby, assuming we evolve from a Big Bang 20 billion years ago, commented: "Since emerging from the iodine-rich oceans to become mammals, we have evolved in an iodine-poor environment."
... It is understandable why someone who believes in the theory of evolution has a problem with such high requirements for iodine in an environment depleted of this element. Unless sometimes in the distant past, the topsoil of planet earth contains significant levels of iodine and meeting these high requirements for iodine sufficiency could then be achieved with any diet. The theory of evolution does not offer an intellectually satisfying answer to this paradox. However, the Biblical account of the origin of the world through creation 6000 years ago followed by the fall of man and the flood fits very well the current situation. According to the biblical narrative, the Creator declared planet earth and everything in it perfect. Therefore, the original planet earth contained a topsoil rich in iodine, and all elements required for perfect health of Adam, Eve and their descendants. A rebelled archangel was expelled from God's Habitation for attempting a hostile takeover (Isaiah 14:12-15). His name was Lucifer before the attempt (Isaiah 14:12) and Satan after his expulsion (Luke 10:18). Satan deceived Eve into believing that she could become a goddess by disobeying her Creator (Genesis 3:4,5). A sequence of events followed, culminating in the worldwide flood 4500 years ago. Following this episode, the receding waters washed away the topsoil with all its elements into oceans and seas. The new topsoil became deficient in iodine and most likely other essential elements, whose essentialities are still unknown. Mountainous areas became the most iodine-deficient because the receding waters were the most rapid over the steep slopes, eroding deeper into the soil.
The Biblical account of the flood fits very well with the finding of high concentrations of iodine in brines, which accompany oil wells and natural gas deposits.8 By 1977, the brines associated with deposits of natural gas in Japan accounted for 56% of the world iodine production.16 The previous existence of iodine-rich living organisms from which came these iodine-rich degradation products strongly suggests that sometime in the distant past, iodine was plentiful on planet earth, and some catastrophic event resulted in washing away the iodine-rich top soil in the oceans.