The phrase "astonishing extent" is correct and usable in written English.
It can be used to describe a degree or level of something that is surprising or remarkable.
Example: "The research revealed an astonishing extent of biodiversity in the region, far beyond what scientists had previously anticipated."
Alternatives: "remarkable degree" or "incredible level".
To an astonishing extent, heritage languages spoken at an early age are not forgotten.
According to the book, Mr. Obama's life was to an astonishing extent "the product of randomness".
Barack Obama's life, says his latest biographer, David Maraniss, was to an astonishing extent "the product of randomness".
And to an astonishing extent, the social blowback for such miscreants is often transient and relatively minor.
He has performed a great service in revealing the astonishing extent and ambition of the national security state".
To an astonishing extent, the way they came to think and talk about their employees was shaped by the movie they had seen so many years earlier.
Still more astonishing was the extent to which the super rich got rich faster than the merely rich.
And then we see a series of galleries that to an outsider is astonishing, demonstrating the extent to which nearly everything about Seattle is engineered.
"It is astonishing to me the extent to which the term re-engineering has been hijacked, misappropriated and misunderstood," Dr. Hammer told Time, saying that ideally, re-engineering should promote greater production and create more jobs.
In Peter Cole's rich new anthology, the extent of their astonishing achievement is fully revealed for the first time in English.
But the idea that it's not going to be married to a social compact, that how you distribute the benefits of capitalism isn't going to include everyone in the society to a reasonable extent, that's astonishing to me.
