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There have been disagreements among various scholars on the origin of all elements in the periodic table starting from hydrogen to uranium with different theories being developed. It is believed that the universe was unchanging, eternal, simple consisting of a single galaxy with few million stars 100 years ago. Today, the universe has changed a lot whereby there are more than 100 billion galaxies with each having more than 100 billion stars. Many features have emerged guided by the laws of physics over a period of more than a billion years.
The big bang theory is one of the theories that attempt to explain the origin of elements in the universe. It is worth to note that about 73 percent of the mass in the universe is made up of hydrogen while helium represents about 25 percent. The abundance of more massive elements (with A>4) is quite low though they form the largest part of our bodies and the earth. Low mass elements which include helium and hydrogen were produced in a hot and dense condition during the birth of the universe. The birth, life as well as death of a star are explained in terms of nuclear reactions. All chemical elements which make up the matter found on the universe were created during these reactions.
The universe, approximately 15 billion years ago began as an extremely dense and hot environment according to the big bang theory. After its formation, it began to cool and expand. High energy density yielded particles and antiparticles and as they collided with each other, annihilation occurred. As cooling was taking place in the universe, average energy of radiation reduced. It is at this point when particle creation occurred until the temperatures were cool enough. After the cooling of the universe, the creation of elements stopped as it become energetically impossible. Some elements were formed in the hot and dense condition such as hydrogen and helium while others were formed in a cooler and less dense condition like Uranium.