Is it 脅かす【おどかす】 or 脅かす【おびやかす】? This explanation says, > the target which threatens is not a person but abstract things such as a society, a nation, a status, peace, happiness and the like. Is the reading of this sentence therefore the following? > > _The rich ocean is threatened by garbage._ rich threaten threaten <

You are correct, it is . Generally is used for "to scare".

* {} Modern times when humanity threatens earth



is ok to me, so I'm not sure "the target must be abstract" part of the explanation. Or some concrete things can be treated as abstract.

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By the way it is {}. {} could be an okurigana variation and as a name, it can be {}.