Stardust In Us

Created by Sarah Choi (prompt writer using ChatGPT)

Stardust in Us — Elements We Share with Stars (Kitchen‑Measure Guide)

We often say we are “made of stardust.” That line is literal, not just poetic. The early universe made almost only hydrogen and helium. Every heavier element—carbon in our cells, oxygen in our blood, calcium in our bones, iron in our hemoglobin—was forged later inside stars and in the explosions and winds that end or punctuate their lives. Those stellar ashes mixed into new clouds, from which our Sun and planets formed. When you breathe, move, or think, you are using atoms minted in ancient stars.

This article explains, in plain terms, which star‑made elements make up most of you and how much of each you carry, translated into familiar kitchen measures for a typical 70‑kilogram (154‑pound) adult. These are simple, order‑of‑magnitude pictures, not exact medical doses—real bodies vary with size, age, and biology, and inside you these elements exist in compounds (like water and minerals), not as pure metal powders or gases.

Where your atoms come from (the short tour)

Hydrogen was born in the Big Bang and now fuels stars. Carbon and oxygen are built in stellar cores when helium fuses (the “triple‑alpha” path to carbon and subsequent reactions to oxygen). Nitrogen is made mainly in stars that run the CNO fusion cycle and in certain late‑life phases of giant stars. Silicon, sulfur, calcium, and magnesium—so‑called “alpha elements”—form in massive stars and are spread by core‑collapse supernovae. Sodium, potassium, and chlorine arise in advanced burning stages and explosive nucleosynthesis. Iron and many iron‑peak elements are produced in supernovae, especially thermonuclear (Type Ia) explosions of white dwarfs. Still heavier trace elements such as iodine and selenium are assembled by slow and rapid neutron‑capture in giant‑star envelopes, supernovae, and neutron‑star mergers. In short: stars light the sky and stock the periodic table.

Kitchen‑counter stardust: how much of each element is in you?

Below, volumes are given as water‑equivalent for easy intuition (1 gram ≈ 1 milliliter ≈ ⅕ teaspoon). Pure elements often pack more tightly or loosely than water; when that matters most (like iron or calcium), a note explains the difference. All figures are for a 70‑kg (154‑lb) person; to scale, multiply by your body mass divided by 70.

The Big Four (about 97% of you by mass)

Oxygen (~65%). You carry about 45.5 kilograms of oxygen—mostly bound into water and organic molecules. As a kitchen picture, that’s roughly 45.5 liters, about 190 cups or 12 gallons. This is the largest single slice of your mass.

Carbon (~18.5%). Carbon is the backbone of life’s molecules. In mass, that’s about 12.95 kilograms—around 13 liters, 54 cups, or 3.4 gallons in water‑equivalent volume. Packed as pure graphite (which is denser than water), the space it would occupy would be closer to 5.7 liters.

Hydrogen (~10%). Hydrogen atoms are tiny but numerous, chiefly in water and hydrocarbons. You contain about 7.0 kilograms, roughly 7 liters—about 29 cups (just under 2 gallons).

Nitrogen (~3.2%). Essential to proteins and DNA, nitrogen totals about 2.24 kilograms, or 2.24 liters—about 9⅓ cups.

Structural minerals (hard tissues and energy chemistry)

Calcium (~1.5%). Most calcium lives in your skeleton and teeth. That’s about 1.05 kilograms—roughly 1.05 liters, 4⅜ cups by water‑equivalent. If imagined as compact metallic calcium (denser than water), it would occupy closer to 0.68 liters (about 2¾ cups). In reality it’s bound in mineral crystals such as hydroxyapatite.

Phosphorus (~1.0%). Partner to calcium in bone and central to ATP energy transfer, you carry about 700 grams—around 700 milliliters, or just under 3 cups.

Electrolytes and essential salts (cell signaling and fluids)

Potassium (~0.35%). Key for nerve impulses, about 245 grams—roughly 245 milliliters, ≈1 cup (a cup plus a teaspoon).

Sulfur (~0.25%). Present in amino acids and vitamins, about 175 grams, roughly 175 milliliters, or about 12 tablespoons (¾ cup).

Sodium (~0.15%). Vital for fluid balance, about 105 grams—105 milliliters, or roughly 7 tablespoons.

Chlorine (~0.15%). Mostly as chloride, paired with sodium and potassium, again about 105 grams—≈7 tablespoons.

Magnesium (~0.05%). Used in hundreds of enzymes, about 35 grams—35 milliliters, or roughly 7 teaspoons (≈ 2 tablespoons + 1 teaspoon).

Trace metals and micronutrients (tiny amounts, big roles)

Iron (~0.006%). Carrier of oxygen in hemoglobin, totaling about 4.2 grams—4.2 milliliters, or just under 1 teaspoon by water‑equivalent. As a compact iron bead (iron is ~8× denser than water), that would be only about 0.53 milliliters, roughly one‑tenth of a teaspoon—a powerful reminder of how little iron does so much.

Zinc (~0.0032%). Enzymes and gene regulation, about 2.24 grams—≈½ teaspoon by water‑equivalent.

Copper (~0.0001%). Energy and connective tissue chemistry, about 70 milligrams—far less than a single drop by volume (≈ 0.07 milliliter).

Iodine (~0.000004%). Thyroid hormones, about 2.8 milligrams—a literal trace, thousands of times less than a teaspoon.

Selenium (~0.000002%). Antioxidant systems, about 1.4 milligrams—again, a trace, nowhere near a measurable fraction of a teaspoon.

Rule‑of‑thumb scaling: per 10 kilograms (22 lb) of body mass, think Oxygen ~6.5 L, Carbon ~1.85 L, Hydrogen ~1.0 L, Nitrogen ~0.32 L, Calcium ~150 mL, Phosphorus ~100 mL, Potassium ~35 mL (7 tsp), Sodium ~15 mL (3 tsp), Magnesium ~5 mL (1 tsp).

A note on volumes vs. reality

Kitchen measures are volumes, but your body stores elements in compounds with water, carbon, and mineral lattices. We used water‑equivalent volume (1 g ≈ 1 mL) to give a mental picture you can pour into a measuring cup. If you imagined pure elemental lumps, the volumes would change with density: iron and copper would take much less space than the water‑equivalent estimate; carbon as graphite would take about half the space; sodium metal would take a bit less; and oxygen as a room‑temperature gas would take an enormous volume unless it were bound. The point is not laboratory precision, but a grounded sense of scale.

Bringing the stardust story full circle

Every cup, tablespoon, and teaspoon above traces back to stellar forges. Carbon and oxygen in your cells were cooked in earlier generations of stars and scattered by their winds and supernovae. Calcium and phosphorus in your skeleton came from massive stars’ last breaths. Iron in your blood was minted in exploding stars and dispersed into the nebula that became our Solar System. When gravity recycled that enriched gas into a new star and planets, some of those atoms ended up here—organized by biology into you. That is what it means, quite literally, to be made of stardust.

Estimates are rounded for clarity and assume a 70‑kg (154‑lb) adult. To tailor them to you, multiply each number by your own body mass divided by 70.