We are stardust. What does this quote mean?

We are stardust

Some people say we are stardust because our bodies are made up of atoms that come from old stars that exploded long ago.

The process of formation of complex atoms

After the Big Bang, there were only hydrogen atoms. A hydrogen atom consists of only one proton and one electron. The force of gravity created large accumulations of hydrogen under enormous pressure. The hydrogen atoms fused into helium atoms that have two protons and two electrons. Nuclear fusion continued and formed heavier and more complex atoms. The types of atoms generated in the successive stages of nuclear fusion were hydrogen, helium, carbon, oxygen, etc. The temperature continued to rise and heavy elements such as magnesium, sulfur, silicon, nickel, cobalt, and iron formed. The most accepted theory is that elements heavier than iron are formed in supernovae.

When stars reach the end of their lives, they often explode and spread their atoms throughout space.

The force of gravity grouped together the remains of the stars that had exploded, and new stars and planets formed. In our case, the new star was the Sun and the planets were the Earth and her other companions in the Solar System. The spontaneous chemical reactions of the Earth’s inorganic matter formed organic molecules, which long after were transformed into the first microscopic living organisms.

A study has been conducted using the Sloan Digital Sky Survey exploration program. The composition of 150,000 stars belonging to the Milky Way have been analyzed, and the elements that are fundamental to life on Earth (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur) have been identified. The conclusion is that 97% of the mass of the human body is made up of matter from stars.


Who said “We are stardust” and “We are made of stellar ash”?

Joni Mitchell in her 1970 song Woodstock said: “We are stardust | Billion year old carbon | We are golden | Caught in the devil’s bargain | And we’ve got to get ourselves | Back to the garden”. Three years later Carl Sagan would write “…our bodies are made of star-stuff” in his book “The Cosmic Connection: An Extraterrestrial Perspective”. Later, in the documentary series “Cosmos”, Carl Sagan said: “We are made of stellar ash. Our origin and evolution have been tied to distant cosmic events. The exploration of the cosmos is a voyage of self-discovery“.


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