what is difference between grounding and earthing?

Nothing, grounding is term used in North America , especially US, earthing is used in mostly in Europe or in Asia those countries colonized formerly by British, like in Malaysia , earthing is commonly used instead of grounding.

The Atlantic Ocean!

I like the humour Sivak.
I hate saying it, but it depends....
Power systems, and national standards on the two sides of the Atlantic, use the term ground and earthing.
But, European standards will distinguish in electronic circuits, the difference between ground- typically metal work, versus earthing, which is a copper rod into mother-earth. As I said, it depends ...especially which standard and what you are upto, and the level of detail.