Cosmos contains all the elements present on the Periodic Table. From light gases, such as helium, to heavy metals, such as lead. But how were all the elements in the universe formed? The creation of elements begins in the early moments of the Big Bang.
The cosmos was only a few seconds old, and the entire space was packed into a volume millions of times smaller than it is today. Due to incredibly high densities, the average temperature of all the material in the universe was well over a billion degrees.
From Energy to Quarks
The heat was so intense that protons and neutrons could not exist as stable entities. The universe was just a sea of fundamental particles, called quarks and gluons, boiling in a state of raw plasma. But the cosmos couldn’t remain like this for long and began to expand rapidly.
Simultaneously, the expansion allowed for its constant cooling. In this way, quarks aggregated to form the first protons and neutrons. But after a few minutes from birth, the temperature was too low to create new protons and neutrons. So, those early heavy particles were the only ones the universe would ever produce. The initial distribution of the universe saw about six protons for every neutron. Neutrons alone are not stable and decay with a half-life of about 880 seconds. So they began to bind with protons to form the first atomic nuclei.
Of all the light elements, the isotope helium-4, consisting of two protons and two neutrons, has the highest binding energy. This means it is the easiest to form but also the most enduring. From calculations like this, cosmologists can predict that the universe began with a mix of about 75% hydrogen, 25% helium, and a small amount of lithium, which is exactly what astronomers observe.
Stellar Nucleosynthesis
The next phase in the appearance of elements had to wait for the first generation of stars. These began to shine only hundreds of millions of years after the Big Bang. Stars fuel themselves through nuclear fusion, primarily transforming hydrogen atoms into helium. The stars have so much hydrogen available that they can burn for billions of years.
Towards the end of their lives, they switch to fusing helium, transforming it into carbon and oxygen. This is why these two elements are so abundant in the universe after hydrogen and helium. In fact, oxygen is the most common element on Earth, although most of it is bound to silicates that form the ground beneath our feet.
More massive stars, eight times the mass of the Sun, fuse even heavier elements into their cores. Especially in their final weeks, days, and even hours, they create nitrogen, neon, silicon, sulfur, magnesium, nickel, chromium, and iron.
Subsequent Nucleosynthesis
This is the end of the line for the formation of elements within stars. Their intense energies are perfectly capable of producing heavier elements, but fusion beyond iron consumes more energy than it produces. So elements heavier than iron rarely appear in the cores of massive stars. The rest of the elements on the periodic table are produced when stars die.
Smaller stars turn slowly, spewing their material throughout their stellar system. Larger stars explode in violent catastrophes known as supernovas. Both types of death leave behind remnants. In the case of small stars, they leave behind white dwarfs, which are almost entirely made of carbon and oxygen. Larger stars leave incredibly dense spheres of neutrons known as neutron stars.
Whatever happens, all these processes involve a lot of radiation, a lot of energy, and many particles flying at high speeds. In other words, the perfect soup for shaping new elements. It is through these calamities that the rest of the periodic table of elements was born. Thanks to these very intense events, the elements spread beyond the boundaries of their birth stars, into the interstellar mix. There, they aggregate into gas clouds, which eventually come together to form new generations of stars that continue the process of recycling and regenerating elements, slowly enriching the universe.
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