Earth Is About 60 Percent Iron and Oxygen by Weight
The Tesla chief's shorthand for that mix is a rusty ball bearing.
All-In with Chamath, Jason, Sacks & Friedberg · Elon Musk: OpenAI Betrayal, His Future at Tesla, and the Next Big Thing — GrokipediaElon Musk, who runs Tesla, was throwing out what he called interesting factoids about what Earth is made of, measured by mass. He thought it was about 32 percent iron and 30 percent oxygen.
Together, that is about 60 percent, a little over three-fifths, from just two elements. Everything else makes up the other 38 percent.
As shorthand for those numbers, Musk said, "we're basically a rusty ball bearing."
At the surface, there is a lot of silicon, which is sand.
Questions people ask
If Earth is one-third iron, why isn't the ground mostly iron?
Most of it sank early in Earth's history. When the young planet was molten, dense liquid iron drained to the center to form the core, leaving lighter rocky material to float to the top as the mantle and crust where we live.
Where is all that oxygen? The air is mostly nitrogen.
Only a tiny fraction is in the air we breathe. Almost all of Earth's oxygen is chemically locked in rock, in minerals where oxygen is bonded to silicon, iron, magnesium, and other elements. Free oxygen in the atmosphere is less than a millionth of the planet's total oxygen.