How is the sunlight the primary source of energy for our own life?

Its not!

The sun IS the source of:

• solar energy in the form of electromagnetic radiation now
• solar energy in the form of high energy ions accelerated by the suns magnetic field
• weather patterns and large storms at sea
• fossil fuels from solar energy captured by living things in the past

The sun IS NOT the source of:

• geothermal energy
• nuclear energy

Both geothermal energy and nuclear energy originate predominately from supernovas that blew up a few billion years before the sun formed, producing quantities of radioactive elements. Some of these radioactive elements were in the dust cloud that formed the solar system, from which earth got its share when it formed.