``All life on Earth obtains its energy from the Sun''.
Let's get quantitative. What is the physical unit of power? Ans: the Watt.
Power 
energy/time. In the metric system of units, the unit of energy is the
Joule. 1 Watt = 1 Joule/sec. Watts are familiar to us from powers of light bulbs.
What is the Watt rating of the Sun (mysterious scientific fact: it is stamped in black numbers on the north pole of the Sun that no one has ever seen)?
Look up the number in the Appendix of your textbook: the power output of the Sun is
Watts. This is an unfathomably large number. What makes it particularly
incredible is that it has been keeping up this luminosity over geological timescales, i.e.
several billion years. That means the Sun has a huge energy source. What is it?