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Describe how nuclear fusion and other processes in stars have led to the formation of all the other chemical elements.

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Nuclear fusion is the process in which smaller nuclei fuse together to form larger nuclei. An example is the process of nuclear fusion that place in our Sun. Here, hydrogen nuclei fuse together to form helium nuclei. It is believed that the Big Bang (which is the most widely accepted model of the origin of our universe) itself created light elements such as hydrogen, helium, lithium, beryllium, etc. These lighter elements fuse to form heavier elements, up to iron. For a significant fraction of its life, a star generates energy by fusing hydrogen to helium. During its later years (and depending on its mass), fusion may create other elements. Helium fuses to form carbon in many stars. In case of heavier stars, oxygen and other elements (such as magnesium, silicon, etc.) are also formed. These reactions are exothermic. However, formations of heavier elements, beyond iron, are generally endothermic processes (they require energy input). These elements (trans-iron) were formed when a star went supernova. This is the phase in the life cycle of a star when the outer expanding layer of a star is thrown out. This explosion generates enough energy to fuse elements and form trans-iron elements. 

Such processes have formed 92 naturally occurring elements. The rest of the elements are man-made and have short lives.

Hope this helps. 

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ryantphysics | Student

Atoms are differentiated by their Atomic Number, a term that simply means "How many protons are in this atom." Because the protons in the center of an atom are positively charged they naturally want to push away from each other. They are held together by the Strong Nuclear Force, but getting them together takes a LOT of energy. Because of this the most abundant element in the known universe is Hydrogen. 


In space there are huge clouds of hydrogen, just floating. As the atoms come near each other, their mutual gravitational attraction pulls them closer together and they begin to orbit each other. When this happens to enough atoms those closest to the center of the mass get pushed closer together by those on the outside, like being at the center of a large crowd. If there is enough mass available, the gravity becomes so great that the atoms are eventually forced together, creating nuclear fusion. More massive stars push more protons together, creating heavier and heavier elements. The most massive stars eventually explode in what is known as a supernova, and that explosion then flings those heavy elements out into space. The explosion of supernovae is where all heavy elements in the known universe have come from. 

re-ko | Student

Nuclear fusion is the process that allows stars to create energy, and happens when two or more atomic nuclei become bound together in a stable system. This process releases energy because some of the mass from the nuclei that have become fused is converted to energy.

Stars start out their life consisting mostly of hydrogen. The hydrogen will start to fuse into helium and release energy, some of which we see as visible light. Once most of the hydrogen has fused, the star will start to fuse heavier elements. The more massive the star, the heavier the elements it will eventually create because the weight of the star will cause it collapse in on itself and the heat from the collapse will allow fusion of heavier elements. The fusion will create an outward pressure that will temporarily stop the collapse until all the fuel is used up and the star again collapses.

When a very massive star is at the end of its life, it will go supernova and release most of its mass into the surrounding interstellar medium. In this way all of the heavy elements that the star has created during its lifetime are spread out and can then form things such as planets.