Describe how a proton found in a hydrogen gas cloud (nebula), subsequently found itself in an atom of lead on the primitive earth.
Supernova, which is the explosion of a star that expels stellar material with great force are the secrets to the existence of heavy metals such as Lead (Pb). Lead is produce during supernova explosions. Other very heavy elements are also formed during supernova explosions. Many of the heavier metals have very large nuclei so that they are very unstable (radioactive). They undergo radioactive decay where they eject proton or neutron, or a neutron in its nuclei decays into an electron and a proton. The process of radioactive decay makes unstable heavy metals to become more and more stable. Lead is not radioactive therefore it is stable and does not spontaneously decay into lighter elements. Unstable heavy elements therefore decay over time until eventually they become Lead. For example, unstable element Uranium 238 decays over time, resulting in a stable element: Lead.
So how does proton find its way into the atom of Lead? The answer lies in the beginning of stars like our solar system. Like our solar system, stars started from a cloud of hydrogen and dust. As the mass of the dust at the core increases to the size of a star, the pressure at the core crushes the particle to a very high dense material. Due to the immense pressure caused by gravity, the core becomes extremely hot that hydrogen fuses to helium. The fusion of 2 Proton and 2 Neutron produces helium and the light (photon) that is emitted by burning star. So after the explosion and years of radioactive decay, the proton from the stars finds its way into the atom of a heavy metal called lead.
To complete the journey of the proton, let us find out how it arrived into the primitive earth. Going back to the collection of dust and cloud of hydrogen, the less dense particles that where not pulled into the core became the planets that circled around the sun. According to recent studies, radioisotope dating of meteorites suggests that planets formed in the Solar System over shorter timescales than had been thought (Cameron 1). Their results indicate that the cores of Vesta (where the meteorite originated), Mars and Earth all formed sooner after the formation of the solar nebula than previous estimates had allowed. The said document further suggests a more realistic picture that the earth’s core underwent a continual core formation starting 29 million years ago. If this is the case, the supernova that existed during the core formation contributed to the birth of the elements that existed on planet earth. There is even a possibility that the core of the solar system exploded when it collided with another collection of dust and dislodge the other planets, including the primitive earth. The explosion in the same manner produced the Lead from the compressed proton.
Cameron, A. G. Planetary Science: Birth of the Solar System. 29 August 2002. Harvard University Faculty Arts & Sciences. 14 November 2006. www.fas.harvard.edu/~planets/news/W-Hf-NatureNewsViewsAug2002.pdf