The human body is mostly composed of four elements - oxygen, carbon, hydrogen, and nitrogen - which make up over 96% of our body's mass. This is supported by scientific evidence and data from various studies. These elements are crucial for the structure and functioning of biological molecules like proteins, nucleic acids, carbohydrates, and lipids, which are the building blocks of life. Additionally, these elements are highly abundant in the Earth's atmosphere and are essential for sustaining life.