The is a vital organ, and its functioning is essential to life.

The heart is a vital organ, and its functioning is essential to life.
All your other organs may fail, and you will still be alive. Even if your brain stops working, and your heart is healthy, you will be alive in the vegetative state where you won't be conscious at all. However, once your heart stops working, you die, which means it is the most important organ in your body.

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.