They weren’t concerned about rock getting involved.
The concern was that the extreme temperature and pressure caused by the fission event would trigger fusion events of the nitrogen in the atmosphere, which would lead to a chain reaction of fusion of the atmosphere.
Yeh, they did.
They were extremely smart people.
And they considered the possibility of that happening.
They calculated the probability of it happening, considered their known-unknowns and unknown-unknowns in their calculations, and concluded the possibility (including their error margin) was so incredibly low that it wouldn’t happen.
And they were right.
A scary prospect, to be sure.
But ultimately, that’s what experts do.
Anyone can build a bridge that will stay up, but it takes an engineer to build a bridge that only barely stays up.
They weren’t concerned about rock getting involved.
The concern was that the extreme temperature and pressure caused by the fission event would trigger fusion events of the nitrogen in the atmosphere, which would lead to a chain reaction of fusion of the atmosphere.
https://www.advancedsciencenews.com/could-a-nuclear-explosion-set-earths-atmosphere-on-fire/
…and then they did it anyway?
Yeh, they did.
They were extremely smart people.
And they considered the possibility of that happening.
They calculated the probability of it happening, considered their known-unknowns and unknown-unknowns in their calculations, and concluded the possibility (including their error margin) was so incredibly low that it wouldn’t happen.
And they were right.
A scary prospect, to be sure.
But ultimately, that’s what experts do.
Anyone can build a bridge that will stay up, but it takes an engineer to build a bridge that only barely stays up.
And besides, if they were wrong, it would very quickly not matter any more.
They calculated it should be fine, but it remained extremely experimental technology.
But yes they did it anyway.
Not all agreed with the calculations. Notably, Fermi.