The origin of life on Earth is believed to have been initiated by the formation of complex organic molecules, which are primarily composed of carbon, hydrogen, and nitrogen.

These elements are essential for the development of the fundamental building blocks of life, such as amino acids, nucleic acids (DNA and RNA), and other biomolecules.

Carbon is the central element in organic chemistry and is the backbone of all living organisms, forming the complex structures of biomolecules. Hydrogen and nitrogen are also crucial elements that participate in the formation of these organic molecules, providing the necessary bonds and functional groups.

The other sets of elements mentioned in the options are not the primary elements responsible for the origin of life. Oxygen, sodium, calcium, and phosphorus are important for other aspects of life, such as energy production and signal transduction, but they are not the key elements that initiated the formation of the first living organisms.