Origin of Elements in the Universe: An Evolution after Big Bang Explosion

Heavier Elements form inside the core of star through nuclear ( source: NASA)

The planet Earth contains various types of elements which form soil, rocks, air, vegetation, species etc. There are nearly 118 elements in the nature. Every element has its specific properties. You will be surprised to know that these elements were not formed at the time of Big Bang Explosion. After the Big Bang only lighter elements like Hydrogen and Helium were formed. Then how the rest of the element originated? How did the materials for formation of planets and asteroids get formed?

The conditions after the Big Bang were favourable only for the lighter elements and heavier elements were formed much later inside the stars. This process of formation of element is called Nucleosynthesis.

Do you find the process of origin of elements in the universe complex and mysterious? Let us discuss this process in detail.

Formation of elementary particle after Big Bang Explosion

The universe was started with the unimaginably tremendous explosion called Big Bang. The universe was started from very small point which had very high density of energy. After the Big Bang Explosion, the universe started expanding. The universe was just a soup of matter and energy till the first few fractions of second.

Big Bang Explosion
Big Bang Explosion (Source: NASA)

As the universe got cooled by expansion, the formation of quarks took place. The particles and antiparticles were being created form the energy and they were also being combined together to annihilate and release energy. Till the one second after the Big Bang, the quarks were having very high energy which was not allowing them to combine for the formation of neutrons and protons.

After the one second of age, the universe expanded and cooled down to temperature of about 100 billion kelvin (1011K). At this temperature the electrons, protons, and neutrons had formed. But they were moving with very high energy, so the formation of atom was not possible. The neutrons were being created and destroyed by the reaction between protons and electrons. The protons and electrons were being combined to form neutrons and neutrons were decaying into protons and electrons.

With the expansion of universe, the temperature decreased more, so the protons and electrons did not have enough energy to collide and form neutrons. So the number of proton and neutron got stabilized with the ratio of 7:1 respectively.

Formation of lighter elements in the universe

At the 100 second after the Big Bang, the universe expanded to reach the temperature of one billion Kelvin (109 K). At this temperature, neutrons and protons collisions were resulting in the formation of nuclei. The proton was itself the nucleus of the lightest atom Hydrogen. The neutron and the proton combined to form nucleus of deuterium atom which is hydrogen with one extra neutron. These deuterium nuclei collided to form nuclei of Helium. On rare occasions, the collisions of deuterium were also resulting in the Lithium.

Birth of Stars

The universe continued to expand and cool, the atoms of gases collected to form clouds of hydrogen gas. There were no stars and planets present at that time. Only clouds of hydrogen gas were spread across the distance of light years. This era is also called Dark Ages.

At about 200 million year after the Big Bang explosion, these massive gas clouds were contracting due to their own gravity which was increasing pressure and temperature. Due to tremendous pressure at the center, the temperature was so huge that the electrons were stripped from the atoms. Now only the nuclei were moving randomly with very high speed inside the core.

Once the temperature reached the 15 million Kelvin, the hydrogen nuclei had enough energy to collide and fuse to form Helium nuclei. This reaction resulted in the release of tremendous amount of energy. The energy came out of core and counteracted the gravity. This resulted in the equilibrium situation, where the inward pull of gravity was balanced by the outward pressure of fusion energy. When this energy reached the surface, it was radiated to the space and the star started shining.

Formation of heavier elements in the universe

The star continued to shine till the exhaustion of hydrogen gas. When the hydrogen gas got consumed completely, the helium was left as the product of reaction. Since the nuclear reactions had stopped, the gravity started dominating the outward energy pressure and the star started collapsing which increased pressure and temperature. With the rise in the temperature, the helium started participating in nuclear reactions to form carbon. When Helium got finished, the carbon started fusion reaction to form heavier elements like oxygen and silicon. These chain reactions continued till the formation of iron. The iron is most stable element. After the iron no further nuclear reaction took place in the star and after this, the star stopped shining.

During the end stages of life, the star with massive size usually exploded in the form of supernova which resulted in the nebula. The nebula had debris of star which contained these heavier elements like carbon, oxygen and silicon etc.

Crab nebula containing heavier elements in the universe
Crab nebula contains metal rich gas ( Source: NASA)

This debris acted as raw material for the formation of new stars and planets. The planets formed form these materials were rich in these heavier elements. That’s why we see abundance of silicon, carbon, oxygen on the Earth.

The elements heavier than iron require much larger energy. Such a large amount of energy is provided by the supernova explosions. So elements heavier than iron are synthesised in the supernova.


Now we can say that all the materials that we can see around us are produced form the Big Bang Explosion and evolved from the hydrogen. The compounds required for supporting life are also result of this evolution of elements in the universe.

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5 thoughts on “Origin of Elements in the Universe: An Evolution after Big Bang Explosion”

  1. If radioactive decay produces new elements, maybe the universe was originally one gigantic heavy element, and today we only see the remnants. Maybe all the elements today are daughters of billions of years of spontaneous decay, like lead is the daughter element of uranium.

    1. The nuclei of heavy elements are unstable and they tend to decay to nuclei of lighter elements to gain stability. But the stability is highest at the mid region of the periodic table around Fe (iron). The elements lighter than Iron tends to fuse together to become heavier to get stability. Thus, the lighter as well as heavier both element undergo nuclear reaction to reach the stability of Iron.
      If we believe that the universe started with the heavy element like uranium then it will decay and ultimately produce Iron (there may be other stable element heavier than Iron like lead). Uranium cannot decay to produce elements lighter than Iron. There may be some byproduct element like helium in the decay reaction but it cannot explain the large fraction of hydrogen present in the universe. Thus, the large fraction of hydrogen and fusion of hydrogen in star clearly indicate that the universe started with the lighter element not heavier element.

  2. interesting but my question is : is this process going to seize as raw materials run out o is simply going to continue like a cycle

  3. Just to make you aware of a (not small) mistake in the article, and hoping this can be helpful:

    “elements heavier than iron are synthesised in the supernova”

    This is actually false: beyond Iron, neutron capture processes play the major roles in producing the different elements. To date, two main processes of this kind are known: the s-process ( https://en.wikipedia.org/wiki/S-process ) and the r-process ( https://en.wikipedia.org/wiki/R-process ), and only part of the second may happen in supernova! While the fist one takes place during very advanced evolutionary stages of BOTH low-mass and massive stars, not in supernovae.

    1. Thank you Umberto Battino,
      You are right. The s-process, although slow, synthesize elements heavier than Iron. At the time of writing this article, I was not aware of this process. Thanks again for the correction.

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