Mass of People

• About one trillion pounds - https://hypertextbook.com/facts/2006/DanielTouger.shtml
• Compare that to mass of iron - 5% * 6^24 kg= 0.05*6 = 3^23 kg of iron
• Trillion is 10^12 - so almost one trillion pounds of iron per person.

Ie, if you take a heap of people, each owns about 1 trillion pounds of steel. Carbon availability happens to be 4% of that - so we are perfectly fit for turning all iron into high carbon steel.