The iron in blood was made in a star

The Big Bang made hydrogen, helium, and a trace of lithium. Iron was forged later, in massive stars, and scattered when those stars died. The iron in haemoglobin is that debris.

Fusion in a star releases energy only up to the iron group. Silicon burning in a massive star builds nickel and iron in the last day of its life, and the core then collapses because fusing further would cost energy rather than yield it. The supernova, or the wind of a dying lighter star for the smaller contributions, throws that ash into the next cloud. The Sun and the Earth condensed from such a cloud. Every iron atom in the planet, from the core to the haemoglobin, took that route. Burbidge, Burbidge, Fowler and Hoyle set the accounting out in 1957. Later work has changed the yields and the sites. It has not changed the direction: hydrogen in, iron out, and the iron leaves.

Gold, in the next entry, is a different workshop. Iron is the common end of ordinary stellar fusion. You do not need a rare collision to explain the nail, or the blood. You need a star heavier than the Sun, a short and violent old age, and a galaxy that mixes its dead thoroughly enough that a small rocky planet, four and a half billion years later, is full of the leftovers.