Hydrogen and helium are the two most abundant elements in the universe, and hydrogen is the most abundant element in the universe. There is only extremely rare free hydrogen on the earth and in the earth's atmosphere. In the crust, if calculated by mass, hydrogen only accounts for 1% of the total mass, and if calculated by atomic percentage, it accounts for 17%.

Hydrogen is a chemical element with symbol H, ranking first in the periodic table of elements. Hydrogen and helium are the two most abundant elements in the universe, and hydrogen is the most abundant element in the universe. There is only extremely rare free hydrogen on the earth and in the earth's atmosphere. In the crust, if calculated by mass, hydrogen only accounts for 1% of the total mass, and if calculated by atomic percentage, it accounts for 17%. Hydrogen is a chemical element, ranking first in the periodic table of elements. The common elemental form of hydrogen is hydrogen. It is a colorless, odorless and easily combustible gas composed of diatomic molecules, and hydrogen is the lightest gas. Hydrogen is used to treat diseases in medicine. Hydrogen atoms are easily reduced. Hydrogen is very active at high temperature. Almost all elements can form compounds with hydrogen except rare gas elements.

Helium is the least active element, with the symbol of He, and it is one of the rare gases. Helium is a colorless and odorless gas under normal circumstances, and it is the only substance that cannot be solidified under standard atmospheric pressure. Helium is mainly used as protective gas, working fluid of gas-cooled nuclear reactor and ultra-low temperature refrigerant. In addition, helium can also be used as a floating gas because its density is lower than that of air and its properties are stable.

According to the Big Bang theory, the primitive universe is a primitive core with very high density and infinite temperature. It exploded for some reason (in fact, it was the materialization of energy), and energy produced matter according to Einstein's E = MC 2. According to this theory, about 1 1 minute after BIGBANG, half the matter in the universe became protons. Protons and electrons combine to form atoms, which are the simplest elements-hydrogen. At this time, the temperature of the primitive fireball in the universe is extremely high, and the material conspiracy is also great, which leads to the nuclear fusion reaction of hydrogen, and some hydrogen will generate helium through nuclear reaction. But after a period of time, the density of temperature of the universe and helium decreased, and the reaction of hydrogen fusion to generate helium stopped, so most substances in the universe existed in the form of hydrogen, followed by helium.