What is the science behind "grounding" or "earthing"?

Excellent book on the subject is "Earthing" by Clinton Ober and Stephen Sinatra, MD.

One of the things going on in us in addition to inflammation is oxidation. Partially burning oxygen makes these things called free radicals ( positively charged oxygen molecules). The largest negatively charged thing that can quench these is the earth. I didn't believe this initially, so I stuck a voltmeter into the ground. It registered a mild negative charge. Earthing allows us to dump free radicals right into the earth, just by sitting, stand or lying on it.

When I ground and fill I connect to the earths energy field. I picture all that the earth has moving, growing, making in the earths crust and layers down. In a meadow outside it is easier to connect to living energy because we are surrounded by it, the warmth of the sun, fresh air and the breeze circulating oxygen, bugs going about their business, trees, grass and plants going through the process of photosynthesis energy exchange for nutrient and growth and of course animal movement throughout that meadow. In a yoga studio or on our carpet at home we are surrounded by synthetic chemical factory made materials that are dead with no living energy or vitality and often we are breathing stale air with traces of those synthetic materials off gassing.
I hope that helps, I'm sure there is a more scientific explanation. I do like to think about quantum theory and picture all our buzzing humming particles creating energy.