About three-fourths of the mass of the sun consists of which element?

Our star, the Sun, is an enormous ball of hot plasma, and its remarkable power comes from its fundamental building blocks. The vast majority of its mass, roughly three-quarters, is composed of the lightest element in the universe. The remaining quarter is primarily made up of the second lightest element, with only tiny traces of heavier elements making up the rest. This cosmic recipe is quite typical for stars across the universe.

This elemental abundance is a direct consequence of the universe's early history. After the Big Bang, the universe was overwhelmingly made of hydrogen and helium, with virtually no other elements. As immense clouds of this primordial gas collapsed under gravity to form stars like our Sun, they inherited this composition. The Sun's enormous mass creates extreme temperatures (around 15 million degrees Celsius) and pressures in its core, which are the perfect conditions for nuclear fusion to occur.

In this stellar furnace, hydrogen nuclei constantly collide and fuse together, forming helium nuclei. This "proton-proton chain reaction" is the engine that powers the Sun, releasing vast amounts of energy in the process, which we experience as sunlight and heat. Every second, the Sun converts approximately 600 billion kilograms of hydrogen into helium, a process that has been ongoing for about 4.6 billion years and is expected to continue for another 5 billion years.