Although He is the second most abundant element in the universe, it is very rare on earth. Why?

Helium is the second most abundant element in the universe, after hydrogen. It accounts for roughly 24% of the total elemental mass of the universe. The abundance of helium is mainly due to the nuclear fusion processes occurring within stars. During the fusion process, hydrogen atoms combine to form helium atoms, which release large amounts of energy. This energy is what powers stars and causes them to shine.

Helium is a noble gas and has several unique properties. It is the lightest among the noble gases and has the lowest boiling and melting points of any element. Helium is chemically inert, which means it does not react with other elements or compounds under ordinary conditions. One of helium's key properties is that it is a monatomic gas and does not form any stable molecules with other elements.

There are several reasons why helium is rare on Earth, even though it is the second most abundant element in the universe: 1. Earth's atmosphere: Helium is lighter than the other gases that make up the Earth's atmosphere. As a result, helium atoms can easily escape the Earth's atmosphere and dissipate into outer space. 2. Production on Earth: Unlike in stars, the conditions necessary to produce helium through nuclear fusion do not exist within Earth. The primary source of helium on Earth comes from the radioactive decay of heavy elements found underground. However, this process produces helium at a relatively slow rate compared to its escape into space. 3. Industrial uses and consumption: Helium has various applications, such as in cryogenics, high-energy particle research, and medical imaging. Due to these uses and its scarcity, the extraction and consumption of helium have increased over time, further reducing its availability.

In conclusion, the rarity of helium on Earth can be attributed to its properties and behavior, which cause it to escape our planet's atmosphere easily, its limited production through radioactive decay, and its increasing industrial use and consumption. Despite being the second most abundant element in the universe, these factors make helium concentrations on Earth far lower than those found in the cosmos.