The Disappearing Spoon: Chapter 4: Where Atoms Come From: “We Are All Star Stuff” Summary & Analysis

For a long time, scientists assumed that all the elements that currently exist have always existed. When the Big Bang theory emerged in the 1930s, it was assumed that this was coherent with this idea of the elements always existing. However, scientists then began to realize that young stars contain only two elements, hydrogen and helium, and that only older stars contain an abundant variety of elements. In the 1950s, four scientists proposed that the early universe featured mostly hydrogen, plus a little helium and lithium—and nothing else. Stars produce nothing but helium for billions of years but—at a certain point of burning—then begin fusing helium atoms, which results in a proliferation of further elements.

After using up their stores of helium, some stars die, whereas other, bigger ones keep burning until they reach the final element in the periodic table, iron. If a star has produced iron, it won’t produce any further elements. This still leaves the very heaviest elements (from cobalt to uranium). Scientists believe that these are produced when gigantic stars implode into tiny iron cores, then explode outward in a gigantic supernova. A supernova happened in our solar system around 4.6 billion years ago, and the dust cloud that formed as a result eventually became our sun and planets. Several elements are named after the planets in our solar system, including uranium, neptunium, and plutonium.

The way elements behave on gassy giants like Jupiter is so unlike the way they do on Earth, leading scientists to come up with seemingly outlandish speculations about what these planets are like. The weather on Jupiter is similarly extraordinary—there is a hurricane three times the size of Earth that has been raging on the planet for centuries. Scientists use weather maps to explain the placement of elements like helium and neon on Jupiter, which aren’t distributed in the way one might immediately expect.

The rocky planets (Mercury, Venus, Earth, and Mars) formed after the gas giants. At first, all the elements inside Earth were mixed together in a uniform way. Over time, however, they moved around and ended up deposited in different parts of the planet in “clusters.” The relative abundance of certain elements within each solar system is unique, an “elemental signature” determined by the way in which the solar system was originally formed by a supernova. The atomic weight of each element in the periodic table is not fixed across the universe—rather, it is true for our galaxy. Scientists know how the earth, solar system, and galaxy were formed by analyzing the elements in the earth’s crust.

The age of Earth was precisely worked out in the 1950s by a graduate student named Clair Patterson, who had previously worked on the Manhattan Project. He knew that there were three different isotopes (types) of lead on Earth, each with a different atomic weight. Some of this was created by the supernova that formed our solar system, and some came more recently, from uranium. He decided to use the relative abundance of the different isotopes to measure the rate of uranium decay, which would provide an accurate sense of the earth’s age. Although Patterson ran into some initial difficulties, he was maniacally devoted to the project and he eventually managed to estimate that the earth is 4.55 billion years old.

In 1977, Luis and Walter Alvarez, physicist-geologists who were also father and son, studied limestone in Italy that dated from the dinosaurs’ extinction. They found inexplicable red clay along with unusually high amounts of iridium, which is often found on comets. This led them to speculate that a giant asteroid hit the earth 65 million years ago, killing 99 percent of life on the planet. Soon after, this theory was bolstered when a large crater, likely caused by an asteroid impact, was discovered in Mexico. Yet this theory clashed with evidence that the dinosaurs died out gradually over hundreds of thousands of years. Some argued that many asteroid hits had taken place over the course of Earth’s history, each causing the mass extinctions that have happened at fairly regular intervals.

However, Earth is small and asteroid impacts are highly unlikely; what could have caused them to happen in a regular pattern? A scientist named Richard Muller proposed an answer: the sun has a twin, another star called Nemesis, that causes asteroids to hurtle toward Earth at regular intervals. Although even Muller only proposed this idea half-seriously, it would explain a lot of the unresolved questions about the extinction of the dinosaurs. Muller published a book about Nemesis, but few took the possibility of its existence seriously. Other explanations for why a semi-regular rain of comets hits Earth include the possibility that they are pulled by the sun itself. The astrophysicist Carl Sagan memorably said, “We are all star stuff,” referring to the fact that all the elements on Earth (and in the human body) were originally formed inside stars.