Heaven and Earth should be considered proper nouns. Let's capitalize them.

The Earth is our planet, and Heaven we hope is our eternal home. Don't you think we should capitalize both words most of the time?

Some exceptions:
*Adjectives: heavenly, earthly.
*The word "heaven" (or "the heavens") when it refers to the blue firmament or the region of the clouds that pass along the sky.
*The word "earth" when it means one of the basic elements (air, fire, water, earth) or the substance in which plants grow.