This was a Question on Quora and the following was my answer and rather surprising postscript at the end.

I can only give you the perspective from a British point of view and I have to say not only has the word become commonly used, it has unfortunately become over used to the point where it has very little resemblance to its actual meaning.

Awesome; extremely impressive or daunting inspiring awe.

Awe; a feeling of reverential respect mixed with fear or wonder.

In the context used by Americans, the word could be generally taken to mean nothing more than ‘good’ or ‘okay’ as it is so flippantly used. An example being, ‘I’ll call you back tomorrow,’ ‘Thanks, that’s awesome’. It may be very kind of the other party to offer to return the call but I can see no reason for a telephone call to inspire awe, unless perhaps the King had misguidedly rung your number in error but decided to stay for a chat nonetheless.

As a British person I find the over use of the word awesome grates on my nerves, as indeed does the British use of the word ‘like’ which is now used almost as a punctuation mark, scattered about through a sentence for no reason whatsoever.

I’m afraid I didn’t answer your question as to when ’awesome’ came into common use in America, except to say, it should not have. They say that language evolves and it’s only a matter of time before English and American become two separate languages completely different from each other, however they may be wrong as they seem to be merging, an example being the use of the words, ‘gotten’ and ‘gonna’ which have crept into the English language but are not English words.

It’s quite interesting that I have great difficulty understanding American but I’m sure that any American visiting Great Britain would have trouble with English should they come across the many different regional accents that we have in this country.

Well, that’s the best I can come up with by way of an answer and all I can say is, it’s been awesome communicating with you.

As a postscript to this post, I took the time to look up gotten and gonna in the Oxford English dictionary and was somewhat surprised to find them listed, together with gotten, wanna and gotta, although the suggestion was they could be used in conversation but not for use in a serious business letter for example. Sadly, I now expect that it’s only a matter of time before it becomes the norm in the Kings English.